Re: Suntac 80286 Mainboards

Posted on 2019-03-28, 21:51

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

This indicates an error accessing/adressing the Video memory? Tried several VGAs, same result. To my surprise, the board is up after finishing the POST. I can switch the keyboard LEDs and a reboot with Ctrl-Alt-Del works. My guess would be a problem with one of the address lines on the ISA bus. The …

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Re: Dead Forex 386 motherboard :-(. Any solution?

Posted on 2019-03-28, 11:10

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Hi again!. Just to be sure that I am doing it correctly and before continuing with the tests, would this circuit be correct? the leds are of different color: green +5 and red GND. These days I will put the results! :-) It's OK, though as I've mentioned with just 1 LED per color you will get them to …

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Re: need info: detailed comparision of ways accessing above 1mb ram in dos

Posted on 2019-03-28, 10:25

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I'm too lazy to make a table and going into details would take pages of text on each and every of those points - so you get this: What OS? Because there is DOS and "DOS" aka Windows 95+ command line. You might be able to get away with some tricks on 95/98 but not on NT kernels. In general, the well- …

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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Posted on 2019-03-27, 14:58

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Hi, just got the new '245! Already installed it and the pc is now running, even the keyboard error got fixed. Excellent! Hopefully it works now, you've already fixed everything else that was damaged by the spill. Would be happy to read a summary what parts had to be fixed at the end...? Well, the …

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Re: OAK OTI-037c - 800x600 mode ?

Posted on 2019-03-27, 14:09

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by Deunan

in Marvin \ Video

in Marvin \ Video

Edit: How about Realtek cards ? Just seen a few online, approx. from the same time period. Stay well away from any Realtek VGAs. If you think the OAK you have is crappy, you'll find yourself at a loss for words when you test a Realtek. Both performance and video quality are terrible. I found …

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Re: Dead Forex 386 motherboard :-(. Any solution?

Posted on 2019-03-27, 08:42

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Hm, no effect huh. Since you're able to replace the clock gen now I assume it's socketed? Is it inserted in correct orientation (don't just try to rotate it, might get damaged by reversed voltage!) - double check the PCB markings to be sure. I can't see that detail on YT video. This mobo seeems to …

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Re: Dead Forex 386 motherboard :-(. Any solution?

Posted on 2019-03-27, 00:10

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

RDY led is not lit, which is strange. Remove VGA card (Is that a Trident TVGA8900C? Decent VGA for a 386 system.) and try again. Remove RAM and try again. Put a jumper on JP2 middle pins (2-3) and try again. I wonder why it has 40MHz CPU if the clock generator is only 66MHz. Also, someone replaced a …

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Re: Searching for redemption with my LS-486e (need help with MB repair)

Posted on 2019-03-26, 21:20

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I noticed that datasheet and the absence of "darlington" as well. But TIP127A is rather obscure It is indeed, it seems to be a rather unique single PNP with high gain (for a 10A power transistor) and very low saturation voltage. The closest thing I found that should work is D45H8G : https://eu. …

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Re: Olivetti PCS86 won't start - PSU?

Posted on 2019-03-25, 21:45

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The voltage is correct so it's not shorted internally (and as I've said for this to be a problem the mobo would also need to have that resistor shorted). So no need to add a diode, and after all it worked for some time without any problems. I'm just trying to figure out why the PSU was not starting. …

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Re: Olivetti PCS86 won't start - PSU?

Posted on 2019-03-24, 22:34

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

What is the battery voltage now? Did you check? Also, what is it connected to? One terminal should be ground (that goes to battery minus) and the other should go to +5V via a diode and a resistor to limit the charging current. If that resistor is somehow shorted now, the battery might be overloading …

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Re: A brief comparison of 386 FPUs

Posted on 2019-03-24, 12:00

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

What VGA card are you using? Some programs that draw a lot on the screen (and that possibly includes fractint as well if it uses BIOS rather than hand-crafted assembly to output pixels) will flatten the scores due to screen output code taking tons of CPU time. As for AutoCAD it's possible it was …

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Re: Olivetti PCS86 won't start - PSU?

Posted on 2019-03-23, 13:56

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Before with tester I identified the ground on PSU output cable, the cable to connect at the motherboard. I connected only the hard disk drive and floppy drive and powered on the PSU. With tester I tried to check the output voltage ad I found strange values beacause the voltage is always very …

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Re: A brief comparison of 386 FPUs

Posted on 2019-03-22, 10:51

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I found the GREEN MATH 4C87SLC-40 to be very unstable when paired with TI 486SXLC2 at 50MHz. It does work fine at 25MHz so I'm wondering why, bus speed is the same in both cases. Perhaps there some issue with BUSY signal timings in clock-doubled mode?

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Re: 3/486 OPTI495SLC VL-BUS benchmarks

Posted on 2019-03-22, 10:31

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Small update... found some 12ns cache chips and swapped them. Now it works fine with fastest 2-1-1-1 cache timings and 256KB cache. Before it would run reliably only with 128KB cache. With 256KB cache it needed 3-1-1-1 and any performance gains with larger cache were negated. I tested different …

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Re: Olivetti PCS86 won't start - PSU?

Posted on 2019-03-22, 10:20

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Don't turn on these old PSUs without a load connected. They don't like it. You can use old 3.5" mechanical HDD connected to one of the Molex plugs to provide some load for both 5V and 12V rails. This is usually enough to make it start but possibly the voltage regulation will be poor. To actually …

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Re: A brief comparison of 386 FPUs

Posted on 2019-03-22, 10:13

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The 486 FPU isn't really anything magical, if Intel just disabled the entire interger core of a 486 and made it pin compatible with the 387, it would only be as fast as a Cyrix Fasmath. Perhaps not magical but the design did have an interesting feature - the FPU uses the integer ALU to speed up …

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Re: Blown resistor in XT PSU?

Posted on 2019-03-21, 20:06

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

It looks like something spilled near that resistor? Inspect all the electrolytic caps ASAP. That resistor is on the secondary side and should not cause a breaker to trip. What probably happened is a catastrophic cascade of failures: - the resistor blew open - quite likely it was a part of the …

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Re: Looking for an ID/manual/jumpers and more info on this 386 AMD 40MHz board

Posted on 2019-03-20, 15:49

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Nah, if you can't find any connection at all then the chips are using the '244, '245 and '373 (which your board has plenty of) as buffers/latches and that complicates things. You're unlikely to debug that with just a meter at your disposal. There is some battery corrosion though so check this area …

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Re: A brief comparison of 386 FPUs

Posted on 2019-03-20, 14:58

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Very nice! If I might suggest a small change to (hopefully) improve this benchmark: Add some high-contrast numbers to the FPU photo and then use these numbers in the result tables along with the names - this will make the chip identification way easier than using "black top", "gray package", etc. In …

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Re: Looking for an ID/manual/jumpers and more info on this 386 AMD 40MHz board

Posted on 2019-03-20, 13:21

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Visual inspection might not be enough. Use this pinout: https://upload.wikimedia.org/wikipedia/commons/9/9f/ISA_Bus_pins.svg Check all address lines (but above all A0-A11 on the 8-bit slot part) with a meter set to beep on continuity. All of them must be connected to the same big chip, it's not …

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