Measure the VCC pins of the CPU socket before inserting any CPU. Gambling with 5V on a 3.5V CPU is not something I'd recommend. Just measure the pin, and if it reads proper voltage, put the CPU. If the voltage comes incorrect, you know at least what's the problem, and can start investigating the voltage selection jumpers and regulator.

bertrammatrix wrote on 2025-03-22, 10:59:

zami555 wrote on 2025-03-15, 21:52:

It's worth to check pins of booth Sis 85C496 and 85C497. Maybe some lost contact with pads due to cracked solder joints. You could try to press both chips with fingers to potentially allow loose pins to get in contact with pads.
On the other hand which type of SIMM memory have you used? I suggest to use just FPM for tests

Indeed, you should use FPM memory to troubleshoot, if I remember SiS boards with that chipset will only work with EDO if the northbridge is "PR" revision (comparatively rare), which you do not have. In my experience with several similar boards they would not post at all with edo, nor with modules with higher capacity than 32mb (which is certainly not the case here)

I’m not sure how to determine if my ram is fpm or edo.
There are no labels on them which indicate such information.

wbahnassi wrote on 2025-03-22, 12:33:

Measure the VCC pins of the CPU socket before inserting any CPU. Gambling with 5V on a 3.5V CPU is not something I'd recommend. Just measure the pin, and if it reads proper voltage, put the CPU. If the voltage comes incorrect, you know at least what's the problem, and can start investigating the voltage selection jumpers and regulator.

Any of the VCC pins or one specific pin?

Would all the VCC pins measure the same voltage? There seems to be multiple VCC pins for socket 2/3 and I just want to be sure that I measure the correct pin.

Any one of the VCC pins should work. They should all have the same voltage.

byte_76 wrote on 2025-03-22, 15:27:

bertrammatrix wrote on 2025-03-22, 10:59:

zami555 wrote on 2025-03-15, 21:52:

It's worth to check pins of booth Sis 85C496 and 85C497. Maybe some lost contact with pads due to cracked solder joints. You could try to press both chips with fingers to potentially allow loose pins to get in contact with pads.
On the other hand which type of SIMM memory have you used? I suggest to use just FPM for tests

Indeed, you should use FPM memory to troubleshoot, if I remember SiS boards with that chipset will only work with EDO if the northbridge is "PR" revision (comparatively rare), which you do not have. In my experience with several similar boards they would not post at all with edo, nor with modules with higher capacity than 32mb (which is certainly not the case here)

I’m not sure how to determine if my ram is fpm or edo.
There are no labels on them which indicate such information.

The only reliable way I've found is to insert it in to a board known to not support edo - if it doesn't boot - it's edo. Most of the old stuff I find is indeed edo, a lot more then FPM which I imagine got phased out when pentium came out. Some UMC chipset boards have a manual EDO setting in bios- if it's set incorrectly the system usually freezes sooner or later, so it can also be used to figure out what type it is

byte_76 wrote on 2025-03-22, 15:27:

I’m not sure how to determine if my ram is fpm or edo.
There are no labels on them which indicate such information.

Please post a photo of your memory sticks with some zoom on ICs to see what's the marking on them. Maybe we can find some datasheet of such IC to determine the memory type.

Okay but I should get post codes on the post analyzer card or beeps if the system is unhappy with the ram.

This board behaves exactly the same with or without the ram installed.

I’ve checked the chips on my ram, they are FPM modules.

byte_76 wrote on 2025-03-22, 17:06:

Okay but I should get post codes on the post analyzer card or beeps if the system is unhappy with the ram.

This board behaves exactly the same with or without the ram installed.

Not necessarily. All of the SiS boards I tested that way would just appear dead with edo, no post or beep or anything. Granted most were one version or another of LS486e, however that shouldn't matter as like I said it boils down to chipset revision. I ended up purchasing ram known to be FPM at the time only to discover/confirm that none of my freebie "stash" ram was FPM.

Sometimes one can make the distinction with chip markings on the modules, however this is not always reliable as EDO capable memory chips can also be used in FPM mode/ are often found on newer FPM modules. IIRC there is some slight difference in how one (?) of the memory IC pins gets connected that differs between EDO/FPM

Those Alliance chips are FPM, [Fast page mode (AS4C14400) or EDO (AS4C14405) from the datasheet.]
It all sounds like the cpu is not initializing: either wrong jumpers, bad bios or bad chipset.
Does the cpu get warm ?

I used a piece of wire in the cpu pin hole that I marked in blue in the attached image.

I’m getting between 5.01 - 5.89V for all voltage jumper positions and with the jumpers completely removed.

I guess I’m lucky my Intel DX4 100 cpu is still working after having tested it in this board many times 😳

Here’s a view of those jumpers and the resistors behind them and also a pic of the under side of the board where the voltage regulator is soldered and connected to the jumpers.

Hmm sounds like the Vreg is shorted. Also: if the 5v line is going up to near 5.9v that is not good, did you have any additional load on the PSU when you measured ? Like a Hard drive ?

No, I did not add any additional load.

Is there a specific brand and model of voltage regulator that is recommended as a replacement?

Most likely a LM1084 adjustable is what it is, like a LM1084IT-ADJ or equal, they are not expensive.

The earlier testing was not correct. It was the wrong point on the socket. (Sorry, Noob mistake 😅)

Tested again using the point marked in red and got the following readings:

Jumper 3.3V position - 3.5V
Jumper 3.45V position - 3.8V
Jumper 4.0V position - 4.1V
Jumper 5.0V position - 5.1V

Does anyone else have any suggestions of what else I can try to revive this board?

It seems voltage is okay so it should be working with my Cyrix DX2 66 at 3.45V.

I’m still waiting for my BIOS rom programmer but I don’t have another BIOS file yet either.

If you have the voltmeter and are poking around anyway make sure all the other voltages are there. Make sure you find 5v on one of the bios legs and all the other larger easy to measure parts. Just working on a board that had no 5 volts on one of the fusible resistors, turned out to show up after wiggling the power plug excessively, re flowed the solder and seems ok now

Chkcpu wrote on 2025-03-15, 08:59:

Hi byte_76, […]
Show full quote

Hi byte_76,

If you have an (E)EPROM Programmer, can you post a dump of the BIOS chip contents here?
Then I should be able to tell you if the BIOS is corrupted or valid and correct for your board with SMC I/O.
And it will be nice to have for TheRetroWeb as well. 😀

Cheers, Jan

This is the first time that I've used a T48 programmer so I hope that I extracted the file correctly.

I have attached the BIOS image. (zipped file)
Can you check it and confirm whether I saved it correctly and what information you can obtain from it?

byte_76 wrote on 2025-04-04, 17:26:

This is the first time that I've used a T48 programmer so I hope that I extracted the file correctly. […]
Show full quote

Chkcpu wrote on 2025-03-15, 08:59:

Hi byte_76, […]
Show full quote

Hi byte_76,

If you have an (E)EPROM Programmer, can you post a dump of the BIOS chip contents here?
Then I should be able to tell you if the BIOS is corrupted or valid and correct for your board with SMC I/O.
And it will be nice to have for TheRetroWeb as well. 😀

Cheers, Jan

This is the first time that I've used a T48 programmer so I hope that I extracted the file correctly.

I have attached the BIOS image. (zipped file)
Can you check it and confirm whether I saved it correctly and what information you can obtain from it?

Hi byte_76,

Okay, you got the T48 programmer and made the BIOS dump from your B887 board!

I’ve checked this 128KB Award BIOS and it is indeed a Rev.D with BIOS-ID:
02/16/96-SiS-496-497/A/B-2A4IBM89C-00

I used Award’s CBROM and MODBIN tools on this compressed BIOS and everything looks perfect. Apart from a few small differences in the BIOS Setup, the main BIOS module (original.tmp) in this Rev.D BIOS is identical to that of the VER.B “LAZER-TRON” BIOS. This also means that your Rev.D BIOS is correct for your board with SMC Super I/O chip.

I also tested your Rev.D BIOS in the LS-486e emulated machine for SiS 496 chipset in 86Box and it booted fine. This is the POST screen:

So now you know the BIOS is good, and that the fault must be elsewhere.
I hope you will find the problem.

Cheers, Jan