VOGONS


Reply 40 of 137, by PC@LIVE

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pentiumspeed wrote on 2021-11-20, 23:01:
Borrow a lab adjustable power supply and thermal camera. Set it up for 1V and 3A or more on the shorted rail and image the res […]
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Borrow a lab adjustable power supply and thermal camera. Set it up for 1V and 3A or more on the shorted rail and image the rest of board for anything hot with this camera. This is important when you find correct power rail that is shorted.

This what I have set up at work for locating shorted component for the phone repair. I recently fixed a USB storage drive this way. This was a capacitor shorted next to the controller glowed. Not on the 5V or other rails.

Generally, resistance of the short determines how easily seen on thermal imager. Very low ohm resistance tend to trip the over current on the power supply so need to insert 1 ohm 5W resistor in series to get enough watts flowing properly.

Cheers,

Thanks very interesting what you suggest.
Unfortunately I have no friends or acquaintances who have the same hobby for electronics, indeed many of those I know do not appreciate what I do.
Unfortunately, I believe only a few have similar equipment, repair workshops have become quite rare, I often had difficulty in finding spare parts, so much so that now I only order them from the Internet.
Thank you for the suggestion of the 1OHm 5W resistor, unfortunately I don't know how to measure the temperature, not having something that can fit.
Greetings

AMD 286-16 287-10 4MB HD 45MB VGA 256KB
AMD 386DX-40 Intel 387 8MB HD 81MB VGA 256KB
Cyrix 486DLC-40 IIT387-40 8MB VGA 512KB
AMD 5X86-133 16MB VGA VLB CL5428 2MB and many others
AMD K62+ 550 SOYO 5EMA+ and many others
AST Pentium Pro 200 MHz L2 256KB

Reply 41 of 137, by PC@LIVE

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snufkin wrote on 2021-11-21, 12:15:
That crossed my mind for a moment, but I think the internal resistance of a battery (I think AA cells are around 0.2 ohms) would […]
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weedeewee wrote on 2021-11-21, 10:50:
If you're really in a jam and have a few 1.5V or 1.2V batteries laying aroung, you could use those to do short detection. One t […]
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If you're really in a jam and have a few 1.5V or 1.2V batteries laying aroung, you could use those to do short detection.
One thing about this method is the chance of batteries going on fire, starting to leak, generally overheating if left shorted for too long.
Though with a 1.5v battery... the chance, i think, is quite low.
There's only so much power the tiny battery can deliver.

That crossed my mind for a moment, but I think the internal resistance of a battery (I think AA cells are around 0.2 ohms) would mean there'd be nearly no voltage across the rest of the circuit, so almost all the power from the battery would just be used to heat up the battery. It's also really not that hard to remove one or two capacitors. It's almost certainly easier than trying to identify in circuit which one might be at fault.

Of course, it may be neither and the problem is somewhere else. What's going to use 1.5V on the board? I know (just read on a datasheet) that the CPU needs it for a termination voltage (slot pins A1, A3, B5, B9). What else? Maybe AGP, although I think this board looks like it's got a 3.3V slot?

Actually, may be worth having a close look at pins A1, A2 and A3 on the CPU slot. Datasheet shows 1&3 at Vtt (1.5V) and 2 is GND. Could be a physical short there if the pins are damaged or there's debris in the slot.

Thanks for what you suggest.
Well if necessary I have several poor PC power supplies, obviously even if they work I don't use them, but I don't know if they have short circuit protections, they certainly don't have the one for overvoltages.
As for soldering, I already use that technique of putting a little new tin on the old solders, it is almost always effective, and allows me to easily remove the broken components, I also use it with SMDs but I happen to remove or solder very few. even after years.

Regarding the batteries, I had heard this solution before, but I thought they used something more powerful, like an element of a car battery (for example).
However in fact if all goes well it should not be difficult to remove both SMDs, the only thing that scares a bit is to spoil the (tiny) tracks, if it helps a lot I could see to order the flux and postpone until it arrives.
Speaking of Batteries, today I managed to buy spare ones for the analog tester, I took some alkaline ones, the 1.5V ones are 2650mAh, and I think they are better than those commonly used, I think they are also good for digital cameras, I have one that fails to start with normal batteries.
I replaced the two 1.5V batteries in the analog tester, and after the replacement it returned to 0OHm setting X1OHm, so I tried to measure the four SMDs tested with the Atlas.
The measurements are as follows:
BC39 0.09OHm
BC35 0.08OHm
BC41 about 15OHm
BC40 3.2OHm
From these measurements it seems to me that both BC39 and BC35 are shorted, while the other two should be fine.
Those BC39 and BC35 checking with the analog tester are connected to ground on one side and to 1085 on the other, so if they were after removal ok, the problem could be from the track onwards, you should understand where they go?
In case they are ok I will try to look in the areas you suggest, to see so there does not seem to be dirt or tracks connected accidentally, in case I try to clean the slots1 and AGP, so I think it does not hurt a bit of cleaning

Greetings

AMD 286-16 287-10 4MB HD 45MB VGA 256KB
AMD 386DX-40 Intel 387 8MB HD 81MB VGA 256KB
Cyrix 486DLC-40 IIT387-40 8MB VGA 512KB
AMD 5X86-133 16MB VGA VLB CL5428 2MB and many others
AMD K62+ 550 SOYO 5EMA+ and many others
AST Pentium Pro 200 MHz L2 256KB

Reply 42 of 137, by PC@LIVE

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weedeewee wrote on 2021-11-21, 10:50:
If you're really in a jam and have a few 1.5V or 1.2V batteries laying aroung, you could use those to do short detection. One t […]
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If you're really in a jam and have a few 1.5V or 1.2V batteries laying aroung, you could use those to do short detection.
One thing about this method is the chance of batteries going on fire, starting to leak, generally overheating if left shorted for too long.
Though with a 1.5v battery... the chance, i think, is quite low.
There's only so much power the tiny battery can deliver.

Thanks I will consider your suggestion, but for now I should try to remove two SMDs that seem to be shorted (at least from several measurements with the testers).
I have recovered a MB to recover some good SMD capacitors, but I have others that I can use, it depends if the color is important (in addition to the size), to see the ones I should remove seem gray or dark purple, while those present in the recovery MB they are mostly beige and brown in color.

Greetings

AMD 286-16 287-10 4MB HD 45MB VGA 256KB
AMD 386DX-40 Intel 387 8MB HD 81MB VGA 256KB
Cyrix 486DLC-40 IIT387-40 8MB VGA 512KB
AMD 5X86-133 16MB VGA VLB CL5428 2MB and many others
AMD K62+ 550 SOYO 5EMA+ and many others
AST Pentium Pro 200 MHz L2 256KB

Reply 43 of 137, by snufkin

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PC@LIVE wrote on 2021-11-21, 21:54:
The measurements are as follows: BC39 0.09OHm BC35 0.08OHm BC41 about 15OHm BC40 3.2OHm […]
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The measurements are as follows:
BC39 0.09OHm
BC35 0.08OHm
BC41 about 15OHm
BC40 3.2OHm

Glad your meter is working again, that's a proper short short. I think BC40 is 5V to Gnd, so you'd expect the resistance to be quite low given the number of things connected to it. I think BC41 is from pin 1 of the 1085 to Gnd, so the value doesn't look too odd.

From these measurements it seems to me that both BC39 and BC35 are shorted, while the other two should be fine.
Those BC39 and BC35 checking with the analog tester are connected to ground on one side and to 1085 on the other, so if they were after removal ok, the problem could be from the track onwards, you should understand where they go?
In case they are ok I will try to look in the areas you suggest, to see so there does not seem to be dirt or tracks connected accidentally, in case I try to clean the slots1 and AGP, so I think it does not hurt a bit of cleaning

If removing those 2 capacitors doesn't clear the short then it must be somewhere else. I'm fairly sure the AGP slot on that board is only 3.3V, so the only thing I know that uses the 1.5V supply are those 4 pins on the Slot 1 connector. If you can post a decent photo of the front and back of the board showing the area around the Slot 1 and the 1085 then if we're lucky we might be able to see where the trace goes, but it might go on an internal layer so we can't see it.

Reply 44 of 137, by PC@LIVE

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snufkin wrote on 2021-11-21, 23:28:
Glad your meter is working again, that's a proper short short. I think BC40 is 5V to Gnd, so you'd expect the resistance to be […]
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PC@LIVE wrote on 2021-11-21, 21:54:
The measurements are as follows: BC39 0.09OHm BC35 0.08OHm BC41 about 15OHm BC40 3.2OHm […]
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The measurements are as follows:
BC39 0.09OHm
BC35 0.08OHm
BC41 about 15OHm
BC40 3.2OHm

Glad your meter is working again, that's a proper short short. I think BC40 is 5V to Gnd, so you'd expect the resistance to be quite low given the number of things connected to it. I think BC41 is from pin 1 of the 1085 to Gnd, so the value doesn't look too odd.

From these measurements it seems to me that both BC39 and BC35 are shorted, while the other two should be fine.
Those BC39 and BC35 checking with the analog tester are connected to ground on one side and to 1085 on the other, so if they were after removal ok, the problem could be from the track onwards, you should understand where they go?
In case they are ok I will try to look in the areas you suggest, to see so there does not seem to be dirt or tracks connected accidentally, in case I try to clean the slots1 and AGP, so I think it does not hurt a bit of cleaning

If removing those 2 capacitors doesn't clear the short then it must be somewhere else. I'm fairly sure the AGP slot on that board is only 3.3V, so the only thing I know that uses the 1.5V supply are those 4 pins on the Slot 1 connector. If you can post a decent photo of the front and back of the board showing the area around the Slot 1 and the 1085 then if we're lucky we might be able to see where the trace goes, but it might go on an internal layer so we can't see it.

Thanks, I'm glad it's working now too, I didn't want to buy another one.
With that tool, some time ago I checked the lines, if it is of interest to the results are these:
Orange PIN 1-2-13 + 3.3V 1.25OHm
Red PIN 4-6-21-22 + 5V 6.5OHm
Gray PIN 8 PWR OK 29OHm
Purple PIN 9 + 5VSB 1KOHm
Blue PIN 14 -12V 5OHm
Green PIN 16 PS_ON infinite
White PIN 20 -5V infinite
Yellow PIN 12 + 12V 10OHm
Measuring them now some values ​​are slightly lower, for example the + 5V drops to 3OHm, the gray drops to about 15OHm, the yellow (+ 12V) to 9OHm, the blue I don't know why before it marked and now after a couple of attempts it doesn't marks more (the needle does not move), but I was interested in understanding if there was a short in the + 3.3V (orange), well I detected a value almost equal to 1.2OHm, so I would say that it should be okay, and I would say that for the moment I focus on those two suspicious SMDs (a lot), I hope tomorrow to unplug them and test them (hopefully good).
For the second problem, that is that of the fan sockets, I am not looking for what is wrong, if I solve it and the card works again, then if they continue to fail I try to look for why.
However, since tomorrow I should do soldering or desoldering, I will try to replace the capacitors on an MB ASRock K7VT4A PRO, I change all four (3300uF 6.3V) even if two or three are swollen, it is a job that if there are no hitches, it is done in a short time and almost always brings the MB back to life.
For the photos of the Slot1 and 1085 areas, I would say that if after removing the short film disappears, I would avoid doing them, if it should remain I will try to do some details, but it is almost impossible to see the tracks under Slot1 where they go, if there are tracks intermediate I would say it is impossible.
For the AGP from memory I seem to remember that it is 2X on the BX, and the confirmation should be there by seeing the notch present, it is located closer to the back of the PC, while in motherboards with AGP4X it is on the opposite side, so I also think 'I don't have + 1.5V voltage in that slot.

AMD 286-16 287-10 4MB HD 45MB VGA 256KB
AMD 386DX-40 Intel 387 8MB HD 81MB VGA 256KB
Cyrix 486DLC-40 IIT387-40 8MB VGA 512KB
AMD 5X86-133 16MB VGA VLB CL5428 2MB and many others
AMD K62+ 550 SOYO 5EMA+ and many others
AST Pentium Pro 200 MHz L2 256KB

Reply 45 of 137, by PC@LIVE

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Today I made other progress on the search for the short on the 6ABX2V, I removed one of the two suspect SMDs (BC39), it was not easy but I managed to remove it without breaking the tracks, the adjacent BC40 one moved a little, but it does not represent one problem, it's just a little crooked.
The removed SMD was tested with the Atlas, and found to be "Open circuit or low capacitance", so it should be fine, in any case it is not shorted.
I'll check if the short is still present, obviously yes!
Moving on to check the back of the PC, a capacitor falls that I had removed for inspection, and at that point I try to see if with the tips on the + and - holes there is short, yes!
At this point I investigate by testing all the capacitors from the back, finding in various parts of the MB, a dozen in short.
One of these could be the cause of the short, evidently the + should be connected by an intermediate track (not visible).
So instead of removing the other SMD, I would opt for electrolytic removal and checking, if I was lucky and found one shorted, I could replace it having solved (maybe ...).
These are precisely these, from 1000uF 10V: EC28 EC36 EC30 EC34, from 100uF 10V: EC29 EC33 EC24 EC35 EC32 EC20, plus the one from 470 uF 6.3V already removed and checked EC21.

I did another job on an ASRock K7VT4A PRO MB, I replaced the four (not great!) 3300uF 6.3V capacitors, the original KZGs were replaced by Rubycon MFZs of equal capacity and voltage.
In the photo you can see before and after the replacement.
I'll see if I can try it tomorrow, but usually it should work, because a couple of the removed ones are short and high ESR.

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AMD 286-16 287-10 4MB HD 45MB VGA 256KB
AMD 386DX-40 Intel 387 8MB HD 81MB VGA 256KB
Cyrix 486DLC-40 IIT387-40 8MB VGA 512KB
AMD 5X86-133 16MB VGA VLB CL5428 2MB and many others
AMD K62+ 550 SOYO 5EMA+ and many others
AST Pentium Pro 200 MHz L2 256KB

Reply 46 of 137, by weedeewee

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Electrolytic capacitors don't tend to fail shorted unless physically damaged, bent or squeezed and even then they'ld have to be abused.

Right to repair is fundamental. You own it, you're allowed to fix it.
How To Ask Questions The Smart Way
Do not ask Why !

Reply 47 of 137, by PC@LIVE

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weedeewee wrote on 2021-11-23, 20:53:

Electrolytic capacitors don't tend to fail shorted unless physically damaged, bent or squeezed and even then they'ld have to be abused.

A ok thanks for the info, sorry but I was late, actually I'm at a loss.
"In circuit Leaky"

AMD 286-16 287-10 4MB HD 45MB VGA 256KB
AMD 386DX-40 Intel 387 8MB HD 81MB VGA 256KB
Cyrix 486DLC-40 IIT387-40 8MB VGA 512KB
AMD 5X86-133 16MB VGA VLB CL5428 2MB and many others
AMD K62+ 550 SOYO 5EMA+ and many others
AST Pentium Pro 200 MHz L2 256KB

Reply 48 of 137, by snufkin

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PC@LIVE wrote on 2021-11-23, 20:26:
Today I made other progress on the search for the short on the 6ABX2V, I removed one of the two suspect SMDs (BC39), it was not […]
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Today I made other progress on the search for the short on the 6ABX2V, I removed one of the two suspect SMDs (BC39), it was not easy but I managed to remove it without breaking the tracks, the adjacent BC40 one moved a little, but it does not represent one problem, it's just a little crooked.
The removed SMD was tested with the Atlas, and found to be "Open circuit or low capacitance", so it should be fine, in any case it is not shorted.
I'll check if the short is still present, obviously yes!
Moving on to check the back of the PC, a capacitor falls that I had removed for inspection, and at that point I try to see if with the tips on the + and - holes there is short, yes!
At this point I investigate by testing all the capacitors from the back, finding in various parts of the MB, a dozen in short.
One of these could be the cause of the short, evidently the + should be connected by an intermediate track (not visible).
So instead of removing the other SMD, I would opt for electrolytic removal and checking, if I was lucky and found one shorted, I could replace it having solved (maybe ...).
These are precisely these, from 1000uF 10V: EC28 EC36 EC30 EC34, from 100uF 10V: EC29 EC33 EC24 EC35 EC32 EC20, plus the one from 470 uF 6.3V already removed and checked EC21.

I did another job on an ASRock K7VT4A PRO MB, I replaced the four (not great!) 3300uF 6.3V capacitors, the original KZGs were replaced by Rubycon MFZs of equal capacity and voltage.
In the photo you can see before and after the replacement.
I'll see if I can try it tomorrow, but usually it should work, because a couple of the removed ones are short and high ESR.

You may already know this, but be careful when measuring resistance across capacitors. The resistance will start out very low, then gradually increase as the capacitors charge up. So make sure you hold the probes on for several seconds and see if the resistance changes. You can be fairly sure that most of the power supplies on the board are ok as the POST card showed they were active. Also, those 10V rated capacitors won't be on the 1.5V supply, more likely they'll be on the 5V supply. The only supply we know there's a problem with, based on the voltage you measured at the start, is that 1.5V regulator.

I'd still expect it'll be one of the ceramics caps that's gone. If you can get photos of the front and back of the board around the Slot 1 then that might help.

Reply 49 of 137, by PC@LIVE

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snufkin wrote on 2021-11-23, 22:02:
PC@LIVE wrote on 2021-11-23, 20:26:
Today I made other progress on the search for the short on the 6ABX2V, I removed one of the two suspect SMDs (BC39), it was not […]
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Today I made other progress on the search for the short on the 6ABX2V, I removed one of the two suspect SMDs (BC39), it was not easy but I managed to remove it without breaking the tracks, the adjacent BC40 one moved a little, but it does not represent one problem, it's just a little crooked.
The removed SMD was tested with the Atlas, and found to be "Open circuit or low capacitance", so it should be fine, in any case it is not shorted.
I'll check if the short is still present, obviously yes!
Moving on to check the back of the PC, a capacitor falls that I had removed for inspection, and at that point I try to see if with the tips on the + and - holes there is short, yes!
At this point I investigate by testing all the capacitors from the back, finding in various parts of the MB, a dozen in short.
One of these could be the cause of the short, evidently the + should be connected by an intermediate track (not visible).
So instead of removing the other SMD, I would opt for electrolytic removal and checking, if I was lucky and found one shorted, I could replace it having solved (maybe ...).
These are precisely these, from 1000uF 10V: EC28 EC36 EC30 EC34, from 100uF 10V: EC29 EC33 EC24 EC35 EC32 EC20, plus the one from 470 uF 6.3V already removed and checked EC21.

I did another job on an ASRock K7VT4A PRO MB, I replaced the four (not great!) 3300uF 6.3V capacitors, the original KZGs were replaced by Rubycon MFZs of equal capacity and voltage.
In the photo you can see before and after the replacement.
I'll see if I can try it tomorrow, but usually it should work, because a couple of the removed ones are short and high ESR.

You may already know this, but be careful when measuring resistance across capacitors. The resistance will start out very low, then gradually increase as the capacitors charge up. So make sure you hold the probes on for several seconds and see if the resistance changes. You can be fairly sure that most of the power supplies on the board are ok as the POST card showed they were active. Also, those 10V rated capacitors won't be on the 1.5V supply, more likely they'll be on the 5V supply. The only supply we know there's a problem with, based on the voltage you measured at the start, is that 1.5V regulator.

I'd still expect it'll be one of the ceramics caps that's gone. If you can get photos of the front and back of the board around the Slot 1 then that might help.

Ok thanks for the tips.
At this moment, I search for the short by removing the suspect capacitors one at a time, removing the SMD BC39 unfortunately I have not detected any changes, but having not removed the BC35 I cannot be sure if it is shorted.
But I thought before taking it off (unsoldering it), I wanted to make sure there was nothing else that could cause the short, and here I found various capacitors that look like it (shorted).
It is true that those capacitors could be on another circuit (5V), but I don't know why then there is a short between the hole of the capacitor (+ and -) EC34, this is on the side near the SB, so I thought maybe they were connected together (through the hole +) with intermediate tracks, from what I know the intermediate tracks are only for ground and perhaps for voltage.
The job I wanted to do was remove the capacitors that seemed shorted (are they connected to each other?), But if you think you don't need it, I'll do other checks.
For the photos I already put some if you have patience I can do various areas, but these days I try with the digital camera, if I can I take a large photo and see to put a link.

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AMD 286-16 287-10 4MB HD 45MB VGA 256KB
AMD 386DX-40 Intel 387 8MB HD 81MB VGA 256KB
Cyrix 486DLC-40 IIT387-40 8MB VGA 512KB
AMD 5X86-133 16MB VGA VLB CL5428 2MB and many others
AMD K62+ 550 SOYO 5EMA+ and many others
AST Pentium Pro 200 MHz L2 256KB

Reply 50 of 137, by snufkin

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Ok, I've put together a rough composite of the various photos and have just realised that 1.5V will need to go to the northbridge. I've traced what I can see of the 1.5V line, and you can see the pins on the back of the Slot 1. B5&9 join together and go through a via, but I can't see if the trace carries on on the top of the board. A1&3 must either connect to an internal layer or to the top of the board:

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The 1.5V from pin 2 of the 1085 connects to several components. There's BC39 & EC21 near the edge of the board. There's BC35 & R94, which are part of the voltage adjust feedback for the 1085. There's also BC42, BC43 and (I think) EC24 which look like they're smoothing nearer the 443BX.

Is it worth taking a close look at the A1,3,B5,9 pins of the slot? If looks as though it has been hit a few time, so maybe a pin has ended up out of place.

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Reply 51 of 137, by PC@LIVE

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snufkin wrote on 2021-11-24, 14:37:
Ok, I've put together a rough composite of the various photos and have just realised that 1.5V will need to go to the northbridg […]
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Ok, I've put together a rough composite of the various photos and have just realised that 1.5V will need to go to the northbridge. I've traced what I can see of the 1.5V line, and you can see the pins on the back of the Slot 1. B5&9 join together and go through a via, but I can't see if the trace carries on on the top of the board. A1&3 must either connect to an internal layer or to the top of the board:
Slot1_1V5.jpg

The 1.5V from pin 2 of the 1085 connects to several components. There's BC39 & EC21 near the edge of the board. There's BC35 & R94, which are part of the voltage adjust feedback for the 1085. There's also BC42, BC43 and (I think) EC24 which look like they're smoothing nearer the 443BX.

Is it worth taking a close look at the A1,3,B5,9 pins of the slot? If looks as though it has been hit a few time, so maybe a pin has ended up out of place.

Thank you so much for your valuable suggestions.
So I did some checks in search of shorts, and I found in suspected short two SMD diodes, the diodes are D6 and D7, the D7 in particular seems to be shorted, but at this point we should understand if it has a connection with the circuit that leads at PIN2 of 1085.
Your photos with the traces, I help me to know where to look, I will do other checks tomorrow in the connected areas that you have indicated, I will see if there is anything suspicious, in particular the EC24 capacitor (close to the 443BX) is in between those that are short, at this point I would try to remove it and see if it is "Leaky" or if it is OK, I would see if the short is between the holes for the + and - pins.
I will also check the Slot1 and the PINs you suggested, but they seem fine inside the slot, in the back of the MB instead there is a point where it took a tap (during transport), I will try to clean up or fix the points that are not perfect, thus preventing them from accidentally making contact with nearby PINs.

Aside from that, I tested a couple of MB, including the ASRock K7VT4A PRO, initially didn't want to know about booting with a Sempron 2600+, so I used a Duron 1400, and even that won't boot, switching to a Duron 1300 instead gives signs of awakening, and shows the various POST codes (also on screen), so it looks OK.
I try to put another similar 256MB RAM (not of the same brand) and it does not start again, so after several attempts I put a 512MB RAM and reassemble the Duron 1400, with this configuration it is working, as a VGA I use a GF4 MX440 AGP8X 128MB DDR, but I also tested a couple of PCI as an alternative, including an 8MB RAGEXL.
For the moment I haven't tried other CPUs, either because I don't have faster Duron (1600 or 1800), and because I have to look for DDR400 or 333 RAM to try a Sempron together.

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AMD 286-16 287-10 4MB HD 45MB VGA 256KB
AMD 386DX-40 Intel 387 8MB HD 81MB VGA 256KB
Cyrix 486DLC-40 IIT387-40 8MB VGA 512KB
AMD 5X86-133 16MB VGA VLB CL5428 2MB and many others
AMD K62+ 550 SOYO 5EMA+ and many others
AST Pentium Pro 200 MHz L2 256KB

Reply 52 of 137, by PC@LIVE

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Today I performed further checks on the 6ABX2V, in particular I checked the SMDs on the PIN2 traces (marked in red), obviously all the SMD capacitors (and not only), are shorted, this is not new now, however after those I pass to verify the PINs of Slot1.
Before testing the PINs I check better inside the Slot1, everything looks fine, except the first PIN (it should be A1), I can see the tab that ended up at the bottom and I would say that it touches the PIN B1, unfortunately it must have bent by inserting the CPU, I hope that this problem is not subsequent to the MB problem, and that by bringing the tab back up (in the right position), the short disappears and the PC can boot.
I honestly don't know what the A1 and B1 PINs are for, unless you then touch other PINs (it seems not), but if they are a positive and a mass, that would explain what causes the short.
The solution would be to fold the tab of the PIN A1 back in place, unfortunately I already know that pulling it up, it is easy for it to break (come off), so at that point the whole Slot1 should be replaced, certainly removing it would perhaps be easier by breaking it, the most boring thing would be to free the holes of the individual PINs, the ideal would be to recover one from a scrap MB, resoldering at the end would be the simplest job.
The only MB from which I can recover slot1, unfortunately has a missing pin, so I don't think it's worth taking it out and trying to fix it, I have no idea if you can find new ones for sale, the alternative would be to take a faulty MB and detach it from there .
But in this case I would prefer to remove it from an irremediably damaged MB, rather than one that can be repaired with a bit of effort and troubleshooting.
Unfortunately, you don't see much from the images, it is still easy to see where there is the empty space, the part at the bottom of the slot cannot be illuminated to be able to distinguish or see better, however it seems to me bent and not broken, I tried to see if by chance it moved and does not move, I will try to make a hook to see if I can pull it up a little, I hope it does not break.

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AMD 286-16 287-10 4MB HD 45MB VGA 256KB
AMD 386DX-40 Intel 387 8MB HD 81MB VGA 256KB
Cyrix 486DLC-40 IIT387-40 8MB VGA 512KB
AMD 5X86-133 16MB VGA VLB CL5428 2MB and many others
AMD K62+ 550 SOYO 5EMA+ and many others
AST Pentium Pro 200 MHz L2 256KB

Reply 53 of 137, by snufkin

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PC@LIVE wrote on 2021-11-26, 20:09:

the first PIN (it should be A1), I can see the tab that ended up at the bottom and I would say that it touches the PIN B1, unfortunately it must have bent by inserting the CPU, I hope that this problem is not subsequent to the MB problem, and that by bringing the tab back up (in the right position), the short disappears and the PC can boot.

That sounds important. Looking here: http://ps-2.kev009.com/eprmhtml/eprma/f706.htm Pin A1 is Vcc1.5 (which is where we're having the problem). B1 is RSVD5-EMI. No idea what that is, but if it's connected to Gnd then that could be the short.

The solution would be to fold the tab of the PIN A1 back in place, unfortunately I already know that pulling it up, it is easy for it to break (come off), so at that point the whole Slot1 should be replaced, certainly removing it would perhaps be easier by breaking it, the most boring thing would be to free the holes of the individual PINs, the ideal would be to recover one from a scrap MB, resoldering at the end would be the simplest job.

Welllll, yes, breaking a pin would be bad. But. There are 4 pins connecting 1.5 to the CPU cartridge, so losing 1 might not actually be a problem.

I'd go for trying to straighten the pin. If survives, then great. If it breaks, then it was already broken, so it's not any worse. If the short has gone then replace the removed capacitors, plug in a power supply, turn on and check voltages. If it all looks ok then plug in CPU and see if anything beeps.

[edit: looking at the photos, it looks a bit close to pin A2, which is definitely Gnd. Move the pin and see if the short goes away.]

[2nd edit: Pentium 2 datasheet says of the EMI pins:

EMI pins should be connected to motherboard ground and/or to chassis ground through zero ohm (0Ω) resistors. The zero ohm resistors should be placed in close proximity to the Pentium II processor connector. The path to chassis ground should be short in length and have a low impedance. These pins are used for EMI management purposes.

So B1 is connected to GND on the motherboard.]

Reply 54 of 137, by PC@LIVE

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snufkin wrote on 2021-11-26, 20:21:
That sounds important. Looking here: http://ps-2.kev009.com/eprmhtml/eprma/f706.htm Pin A1 is Vcc1.5 (which is where we're havi […]
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PC@LIVE wrote on 2021-11-26, 20:09:

the first PIN (it should be A1), I can see the tab that ended up at the bottom and I would say that it touches the PIN B1, unfortunately it must have bent by inserting the CPU, I hope that this problem is not subsequent to the MB problem, and that by bringing the tab back up (in the right position), the short disappears and the PC can boot.

That sounds important. Looking here: http://ps-2.kev009.com/eprmhtml/eprma/f706.htm Pin A1 is Vcc1.5 (which is where we're having the problem). B1 is RSVD5-EMI. No idea what that is, but if it's connected to Gnd then that could be the short.

The solution would be to fold the tab of the PIN A1 back in place, unfortunately I already know that pulling it up, it is easy for it to break (come off), so at that point the whole Slot1 should be replaced, certainly removing it would perhaps be easier by breaking it, the most boring thing would be to free the holes of the individual PINs, the ideal would be to recover one from a scrap MB, resoldering at the end would be the simplest job.

Welllll, yes, breaking a pin would be bad. But. There are 4 pins connecting 1.5 to the CPU cartridge, so losing 1 might not actually be a problem.

I'd go for trying to straighten the pin. If survives, then great. If it breaks, then it was already broken, so it's not any worse. If the short has gone then replace the removed capacitors, plug in a power supply, turn on and check voltages. If it all looks ok then plug in CPU and see if anything beeps.

[edit: looking at the photos, it looks a bit close to pin A2, which is definitely Gnd. Move the pin and see if the short goes away.]

[2nd edit: Pentium 2 datasheet says of the EMI pins:

EMI pins should be connected to motherboard ground and/or to chassis ground through zero ohm (0Ω) resistors. The zero ohm resistors should be placed in close proximity to the Pentium II processor connector. The path to chassis ground should be short in length and have a low impedance. These pins are used for EMI management purposes.

So B1 is connected to GND on the motherboard.]

Thank you so much friend, I think the solution is right near here.
So the PIN A1 is a positive (+ 1.5V), and this I think can be very useful, about the PIN B1 I can see in the scrap MB if it goes to ground, and if it goes here this should be the short that was thought to be close to 1085, and speaking of this shortly gone I should resolder the BC39, I have no new substitutes so if all goes well I'll put it back?
In place of the EC4 and EC34 that I had removed some time ago I would have two OK tested recovery capacitors ready, but if you think it is better to put them new I would have to order them and wait a month or two for them to arrive.
To straighten it I will try to pull it up a bit, but I don't know if it will rise enough or break, in case it breaks and the short disappears you could make a bridge in the CPU, and that PIN must be powered.
So as a first test when finished, should I try without CPU and RAM, or with only RAM?

Ok made sure that the neighboring PINs are ground, I would say that I try to hook it up and pull it up, hoping that it gets back in place and that the short disappears (otherwise you have to search again).

AMD 286-16 287-10 4MB HD 45MB VGA 256KB
AMD 386DX-40 Intel 387 8MB HD 81MB VGA 256KB
Cyrix 486DLC-40 IIT387-40 8MB VGA 512KB
AMD 5X86-133 16MB VGA VLB CL5428 2MB and many others
AMD K62+ 550 SOYO 5EMA+ and many others
AST Pentium Pro 200 MHz L2 256KB

Reply 55 of 137, by PC@LIVE

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For the moment with the 6ABX2V I took one step forward and two backwards, the problem of Slot1 and PIN A1 ended up at the bottom of the slot, it was very complex to solve, I had to remove some plastic (by milling), then with a resistor I hooked it up and pulled it up enough that I could put it back in its housing, I could have found more but the resistor suited the purpose quite well.
Fortunately, even pulling with force it did not come off, perhaps these PINs are quite strong, considering that I was putting a force greater than the weight of the MB, it is not perfectly positioned but in any case it is okay, I tried to insert a CPU Slot1, and the PIN it moves sideways like the others, so for safety I looked inside Slot1, all the PINs appear correctly positioned, and there are no pieces of metal inside that make abnormal contacts.
Unfortunately, the short between the PIns has not disappeared, this makes me think that the Slot1 problem is subsequent to the failure, or that the contact between the PINs of Slot1 caused the failure (of some component) and therefore made the MB not working.
Having several MB awaiting repair, in addition to the scrap, I check the same PINs of Slot1, and in none there is a short one, the value that is usually found is about 120 (digital tester on tester), I think this is the value that you should read when it will work again, surely if I had a second MB 6ABX2V, I could compare the values ​​and look for what is broken.
It seems pretty clear to me that this is something short, from what they suggested days ago, electrolytics shouldn't be broken enough to lead, but if you need to be sure they are good, I can remove and test them, sometimes it happened that even if the measured values ​​were tolerable, replacing them made the card work again (in that case a VGA VLB).
For SMD components, I have seen that some use a tool called "Smart Tweezers" to test them, obviously I don't have it, but testing them after removing them is still a sure way to find which ones are bad.
So, at this point I should start the search for the short again, but I don't know whether to unplug some other SMDs to test it, or look for other components on the MB with suspicious readings.

Attachments

AMD 286-16 287-10 4MB HD 45MB VGA 256KB
AMD 386DX-40 Intel 387 8MB HD 81MB VGA 256KB
Cyrix 486DLC-40 IIT387-40 8MB VGA 512KB
AMD 5X86-133 16MB VGA VLB CL5428 2MB and many others
AMD K62+ 550 SOYO 5EMA+ and many others
AST Pentium Pro 200 MHz L2 256KB

Reply 56 of 137, by snufkin

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Good work lifting the pin, shame the short is still there, that seemed very likely it was the problem. So that means it's back to removing and testing any component that's connected to both 1.5V and Gnd. I'd go back to checking the ceramic capacitors, although you mentioned about a couple of diodes which can also fail short (I fixed a water damaged amplifier recently that turned out to be two diodes gone short). Worst case is that the short is actually inside the Northbridge, but let's hope not. Just be methodical and take it one component at a time.

Reply 57 of 137, by PC@LIVE

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snufkin wrote on 2021-11-27, 20:29:

Good work lifting the pin, shame the short is still there, that seemed very likely it was the problem. So that means it's back to removing and testing any component that's connected to both 1.5V and Gnd. I'd go back to checking the ceramic capacitors, although you mentioned about a couple of diodes which can also fail short (I fixed a water damaged amplifier recently that turned out to be two diodes gone short). Worst case is that the short is actually inside the Northbridge, but let's hope not. Just be methodical and take it one component at a time.

Thank you, only with your suggestions I managed to focus research.
Now I should go in search of the short component, finding it could be possible, except in case both inside the NB, in that case it is impossible to remove it and replace it, even if you want you might try (so much to that broken point for broken ) To remove it with hot air.
With regard to the short of diodes or other, having functionally the analogue tester, I verified the components be with the digital and analogue, with the analog some show some ohms of resistance, this makes me think that maybe there is the Way to distinguish if they are good (without removing them), however I'll try to remove the SMD capacitors and test them, if they go well I would rocket them because so I'm sure not to put them in another position (eronatively).
And wanting to put the electrolytics removed, but maybe if it's simple first I remove the others, the text and then I put them all, even if I'm pretty sure they are all in place, but you never know.
Doing a comparison with the other MBs that I have (to be repaired), this has the + 3.3V line with a low value of ohm, about 1.25, usually stands on the above 3 ohms, sometimes the hand does not move at all , but in those cases it could be a problem in the + 3.3V line, and create operating problems.

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AMD 286-16 287-10 4MB HD 45MB VGA 256KB
AMD 386DX-40 Intel 387 8MB HD 81MB VGA 256KB
Cyrix 486DLC-40 IIT387-40 8MB VGA 512KB
AMD 5X86-133 16MB VGA VLB CL5428 2MB and many others
AMD K62+ 550 SOYO 5EMA+ and many others
AST Pentium Pro 200 MHz L2 256KB

Reply 58 of 137, by PC@LIVE

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Today I tried to rearrange the ideas about the failure of the 6ABX2V, I tried to understand what works and where the failure is, i.e. in which line, according to the measurements made with three different testers, I concluded that the measurements of the analog meter actually show what is in short, with the digital one there is a less reliable indication of short, for comparison I used the Atlas which measures resistances up to 0.01OHm, but some readings can put the doubt (especially if the trace is long?).
Keeping the readings of the selected analog tester OHmX1 good, I double-checked the lines, that of the + 3.3V resulted in short or partially shorted, this unfortunately is an important line for the operation of almost everything is present in the MB, strangely the traces for this line are very few, or they are internal, I think it is a fairly delicate line and in the presence of a problem somewhere, you can find yourself with the MB out of order.
Now maybe I'll be wrong, but in my opinion there is a faulty component interfering in that line, and it's not totally shorted, could it be an electrolytic that drops the voltage? Or could it be a diode leaking a bit?
Regarding the electrolytics, at the moment I have not made checks on the suspicious ones (to be removed), but I have seen that one of those removed, EC34 has the + hole connected directly to the PIN 1-2-13 of the ATX molex (orange wire), so I think there are others connected but for the moment they have not been removed.
Regarding the diodes, in particular two SMDs marked D6 and D7, the D6 I saw that it could be ok, the D7 instead shows a problem, only by removing it you can understand if it is really broken, the readings with the probes of the analog tester are of a few OHm about 4 or 5 (even exchanging them), on the opposite side to the black mark there is the direct line to + 3.3V, so I thought that if it is not good it passes current and creates problems. Unfortunately being SMD you have to remove it, if it had been a normal diode it would have been enough to lift a PIN.
I put a picture of this area to show the diode D7, on the chipset side there is the trace of the + 3.3V, while the D6 is near the 1085, this is also powered by the + 3.3V (orange side), so if one wrong could cause problems to the other? Even if it is good?

Attachments

AMD 286-16 287-10 4MB HD 45MB VGA 256KB
AMD 386DX-40 Intel 387 8MB HD 81MB VGA 256KB
Cyrix 486DLC-40 IIT387-40 8MB VGA 512KB
AMD 5X86-133 16MB VGA VLB CL5428 2MB and many others
AMD K62+ 550 SOYO 5EMA+ and many others
AST Pentium Pro 200 MHz L2 256KB

Reply 59 of 137, by snufkin

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PC@LIVE wrote on 2021-11-28, 20:59:

Today I tried to rearrange the ideas about the failure of the 6ABX2V, I tried to understand what works and where the failure is, i.e. in which line, according to the measurements made with three different testers, I concluded that the measurements of the analog meter actually show what is in short, with the digital one there is a less reliable indication of short, for comparison I used the Atlas which measures resistances up to 0.01OHm, but some readings can put the doubt (especially if the trace is long?).

What's your digital meter? You shouldn't get a big difference between the analog and digital meters.

I don't think your Atlas can measure shorts, I think the resistance it shows is the ESR, which is the effective resistance at a high frequency. At a high enough frequency an ideal capacitor should measure as a short, but at DC it should (eventually) measure as open circuit. The problem here seems to be a DC short. If you've got some resistors around would you mind using your analog and digital meters to measure their resistance and make sure that your readings match the value given by the colour bands? That will tell you if the meters are working ok. Then use the meters to recheck the resistance from pin 2 of the regulator to Gnd (use a Gnd pin on the power connector).

Some power lines on a motherboard can be low resistance (my KA7 measures around 5 ohms on the CPU regulator output), so low doesn't necessarily mean there's a problem. At the start of this I think you said that a POST card showed the 3.3V supply as ok. We know from measurements that you took before that the 1.5V regulator has 5V going to it, and that the resistance from the 1.5V line to Gnd was about 0.1ohm (or less). That means the regulator would have to put out about 15A to maintain a 1.5V output, which is much too high. So there's a definite problem somewhere between that regulator and Ground. I would concentrate on finding the cause of that problem before worrying about things that might not be a problem (like the 3.3V supply).

If you're uncomfortable with having to keep removing SMD components until you find the one causing the problem then maybe the best thing is to go back to checking to see if any component is getting hot. The simple way (although not as accurate as a thermal camera) is just applying power to the board, then start putting your finger on various components until you find one that's hot. Hopefully something will heat up enough for you to find it before the 1.5V regulator overheats and the over-temperature protection cuts in. If you can't find anything, then it's back to removing components until you find the problem.