Do you have another PSU? I know you said it's NOS but you never know, since you've tried multiple boards and also one that did work but then stopped...it's one of the common denominators.

sunkindly wrote on 2025-10-30, 16:12:

Do you have another PSU? I know you said it's NOS but you never know, since you've tried multiple boards and also one that did work but then stopped...it's one of the common denominators.

I only have a 15 years old 500W ATX PSU (the board supports it), I guess it's okay for testing, otherwise no, it has to be AT. 😁 All the AT PSUs that I have come with the PC cases, nothing separately.

For testing old boards I highly recommend getting some AT to ATX PSU adapters so you can use more modern power supplies:
https://www.ebay.com/itm/334858867116

I will admit that I haven't seen a lot of AT PSU failures, but considering the lack of safety and protection features on them and the lack of protections on boards from the time I prefer to use newer units.

Keep in mind that most adapters do not supply -5v from PSUs that do not have it, so you may want to get some voltage blasters at some point as well. Or make your own. 😀

Ozzuneoj wrote on 2025-10-30, 16:58:

For testing old boards I highly recommend getting some AT to ATX PSU adapters so you can use more modern power supplies:
https://www.ebay.com/itm/334858867116

This is interesting... However, the Chaintech mobo does support ATX natively, it has both AT and ATX connectors. I prefer AT only because of that brown "It's now safe to turn off your computer" text, and no momentary switch on the PC case. If a workaround for that exists, then I'd even use ATX as a last resort, because they usually don't have the monitor power outlet.

First I'll have to find out if the problem is in the PSU after all. It does deliver power. The MHz display lights up and the CPU fan runs (both get the juice from Molex). I can check the voltage as soon as I can, based on this: https://pinoutguide.com/Power/MotherboardPower_pinout.shtml

SGM wrote on 2025-10-30, 17:32:

Ozzuneoj wrote on 2025-10-30, 16:58:

For testing old boards I highly recommend getting some AT to ATX PSU adapters so you can use more modern power supplies:
https://www.ebay.com/itm/334858867116

This is interesting... However, the Chaintech mobo does support ATX natively, it has both AT and ATX connectors. I prefer AT only because of that brown "It's now safe to turn off your computer" text, and no momentary switch on the PC case. If a workaround for that exists, then I'd even use ATX as a last resort, because they usually don't have the monitor power outlet.

First I'll have to find out if the problem is in the PSU after all. It does deliver power. The MHz display lights up and the CPU fan runs (both get the juice from Molex). I can check the voltage as soon as I can, based on this: https://pinoutguide.com/Power/MotherboardPower_pinout.shtml

Separate troubleshooting from your definitive configuration. You can have all kinds of requirements for an ideal situation, but first you need to get everything working.

Try the ATX PSU on that board. If that works, it's a strong indication your AT PSU is the problem - and that your board, CPU, mem and VGA are good. If not, it doesn't rule out PSU problems but makes other causes more likely.

Also, what CPU are you using and what RAM - and what jumper settings have you done on the board(s)?

dionb wrote on 2025-10-30, 19:56:

Also, what CPU are you using and what RAM - and what jumper settings have you done on the board(s)?

Here's what I know so far:

I have used two 200MHz MMX CPUs and one 133 Pentium and one 166 MMX. I tried different SIMMs, 32Mb sticks and 4Mb sticks, and I tried in all 4 slots in any combination. No difference in behavior.

Then I tried a working ATX PSU, shorting the "pwr" pins on the mobo with a screwdriver did turn the PSU on so the mobo did work thus far. No image, no beep, the exact same behavior. I shorted the pins for 4-5 seconds to turn it off again.

I checked the AT power output with a digital multimeter. Everything seems to be normal, but 12V and -12V were slightly under, it read 11.8x V instead of full 12V. 5V outputs were more accurate.

As for any jumpers on the mobo, I really didn't see anything to configure, or at least my brain didn't figure it out.

Powering it on does nothing but briefly flash the keyboard LEDs, and that's all. And pressing caps, numlock, scroll lock don't toggle their respective LEDs on the keyboard.

I tried the PC speaker in both polarities, it never beeps, weird. It did beep with the first mobo that came with the PC case itself.

Dont you need 4 sticks od ram for 32 bit cpus ?

two pairs of two.

SGM wrote on 2025-11-03, 08:33:

dionb wrote on 2025-10-30, 19:56:

Also, what CPU are you using and what RAM - and what jumper settings have you done on the board(s)?

As for any jumpers on the mobo, I really didn't see anything to configure, or at least my brain didn't figure it out.

Hi SGM,

Your brain is just fine. 😉

This Chaintech 5TDM2 is a jumperless board, quite unique for a socket 7 board.
The BIOS has Chaintech’s “SeePU” technology with automatic CPU recognition and setup. In the BIOS Setup, you can override this with manual selections for Vcore, FSB, and Multiplier.

If an incorrect BIOS has been flashed, the CPU will not be setup and the board remains dead.
Do you have an (E)EPROM programmer to make a dump of your BIOS chip contents? If so, please put this copy up here and I will check it for you.

Cheers, Jan

Chkcpu wrote on 2025-11-03, 11:14:

Hi SGM,

Your brain is just fine. 😉

hehe 😁

Chkcpu wrote on 2025-11-03, 11:14:

If an incorrect BIOS has been flashed, the CPU will not be setup and the board remains dead.
Do you have an (E)EPROM programmer to make a dump of your BIOS chip contents? If so, please put this copy up here and I will check it for you.

I don't have such tools, I'm still relatively new to this hobby, I started ~1.5 years ago.
The board was sold as "taken from a working machine", and I bought 2 more Socket-7 boards that had the same claims, but none of them get the picture up. This may rule out the BIOS issue IMHO.

The first motherboard that came with the AT case itself did work at first, no issues other than no HDD connected, so no OS either. One day it just didn't POST anymore overnight, only a short beep, no image, and I absolutely didn't change anything since last successful POST. That's when I got the Chaintech board to replace it with, I assumed it will work fine, and you know the rest of the story from this topic.

I have restored several Socket-7 PCs and none of them behaved mysteriously like this one.

nuno14272 wrote on 2025-11-03, 09:40:

Dont you need 4 sticks od ram for 32 bit cpus ?

two pairs of two.

No. These are 72p SIMMs which are already 32b wide. The i430TX has a 64b memory controller without fallback to 32b, so SIMMs need to be installed in identical pairs. You don't need 4 SIMMs, and indeed while troubleshooting it's always a good idea to use the minimum - here a single pair of SIMMs - until you've found out what's wrong.

The manual is pretty clear on this:

You must install 2 SIMM modules(same size, same speed, either single or double sided) in each bank at a time. It does not matter which bank you install first.

For what it's worth this board isn't an "Intel Triton OEM Motherboard SB82371SB SB82437VX HT12888B Houston Tech", it's a Chaintech 5TDM2 (see the big bold letters between the middle PCI slots - and the print on the BIOS EEPROM).

Here's what I know so far:

I have used two 200MHz MMX CPUs and one 133 Pentium and one 166 MMX. I tried different SIMMs, 32Mb sticks and 4Mb sticks, and I tried in all 4 slots in any combination. No difference in behavior.

OK. Those CPUs all require 66MHz FSB. That in turn requires SIMMs that can run at 60ns. 70ns might not work. So do the SIMMs have 60 or 70ns chips? Also are they EDO or FP (shouldn't matter on this board, as long as you don't mix both types).

The board also accepts 3.3V DIMMs and should work with PC66 or PC100 SDRAM DIMMs. Have you tried one of those?

Then I tried a working ATX PSU, shorting the "pwr" pins on the mobo with a screwdriver did turn the PSU on so the mobo did work thus far. No image, no beep, the exact same behavior. I shorted the pins for 4-5 seconds to turn it off again.

Same behaviour for AT and ATX PSUs - including a known-good one - suggests your PSU isn't the problem and it's on the motherboard.

I checked the AT power output with a digital multimeter. Everything seems to be normal, but 12V and -12V were slightly under, it read 11.8x V instead of full 12V. 5V outputs were more accurate.

AT(X) power lines have +-5% tolerance, so for 12V anything between 11.4 and 12.6 is acceptable. The probably reason that the lines weren't at nominal value is that there's actually nothing on an old motherboard that places a significant load on them. I suspect that the +12V at least would tend closer to exactly +12.0V if you hooked up a couple of HDDs.

Measuring voltages is a good idea though. After checking the +5V and +12V lines the next thing to check would be the output of the VRM for the CPU. That should be 2.8V for a Pentium MMX. If that's way out of spec, it could explain why the system isn't starting. After caps, VRM MOSFETs are about the commonest part to fail on an old board.

As for any jumpers on the mobo, I really didn't see anything to configure, or at least my brain didn't figure it out.

Yes, this seems to be a late So7 'jumper-free' design. I don't like them, as if something goes wrong it's a lot harder to figure it out than if you have hard jumpers setting voltage, FSB etc.

Powering it on does nothing but briefly flash the keyboard LEDs, and that's all. And pressing caps, numlock, scroll lock don't toggle their respective LEDs on the keyboard.

I tried the PC speaker in both polarities, it never beeps, weird. It did beep with the first mobo that came with the PC case itself.

To beep requires the CPU to be executing a minimum of BIOS code. If that's not possible, it won't beep.

dionb wrote on 2025-11-03, 13:02:

For what it's worth this board isn't an "Intel Triton OEM Motherboard SB82371SB SB82437VX HT12888B Houston Tech", it's a Chaintech 5TDM2

I guess we have a confusion here, because my current board is Chaintech 5TDM2 which I want to use. That Triton board is the older one which came with the PC case, and I only mentioned it because it worked when I put the PC together, and suddenly one morning it didn't work anymore, and that's when I got the Chaintech 5TDM2 which replaced the old board. And Chaintech 5TDM2 is much superior so I really want to get it to work.

I have some more SIMM pairs to try next, but I don't have any suitable DIMMs, mine are all 64-128Mb PC133 versions which don't seat.

SGM wrote on 2025-11-03, 14:55:

[...]

I guess we have a confusion here, because my current board is Chaintech 5TDM2 which I want to use. That Triton board is the older one which came with the PC case,

"Triton" is the Intel code name for the i430 series of chipsets starting with i430FX, and the rest of that 'name' string is just a list of chipset components on the board. So that's not the name of the board, just some of the chips on it. It looks like it has an i430VX 'Triton II' chipset, which is one generation older than the i430TX of the 5TDM2, but that's hardly 'much' superior, particularly not if you're using FP or EDO SIMMs instead of SDRAM.

and I only mentioned it because it worked when I put the PC together, and suddenly one morning it didn't work anymore, and that's when I got the Chaintech 5TDM2 which replaced the old board. And Chaintech 5TDM2 is much superior so I really want to get it to work.

I have some more SIMM pairs to try next

OK, but what are their specs? As this board automatically selects 66MHz FSB, it will fail if the SIMMs are rated 70ns and don't have much headroom for overclocking. Normally I'd expect some memory beeps in that case, but the one rule of hardware failure is that a system can work in exactly one way but fail in infinitely different ways, many of which do not beep...

but I don't have any suitable DIMMs, mine are all 64-128Mb PC133 versions which don't seat.

PC133 is physically identical to PC66 and PC100, it's all 3.3V (usually) unbuffered DIMM. If it doesn't fit, either the slot is damaged or you're doing it wrong.

It's possible the PC133 may have higher density (256Mb chips) than the i430TX memory controller can address, but in that case it will generally just work at 1/2 the nominal capacity. It might have stability issues in that case, but you can use that to rule out compatibility issues with your SIMMs.

By the way, please watch your capitals when talking about RAM. Mb and MB are not the same (1MB=8Mb). Here what you mean is clear enough from context what you mean, but once we start talking chip densities (normally expressed in Mb, not MB - as I did for the 256Mb chips above) things will get hopelessly confusing