You might need to update the motherboard bios first to use newer Athlon cpus.

In the upper left of the photo I see what appears to be a capacitor with a domed top which indicates that it is failing. That power supply ought to get this system to POST, but 20A +5 will leave little margin for error and could be an issue.

https://www.youtube.com/watch?v=efK7mw8eYiE&t=9s

Make sure that the CPU die isn't chiped.

I did some tests on my gigabyte 7zx and code 85 is related to cmos setting is not saved and when you power up the board, it halts on this code and asks you to hit F1 to enter the bios settings or hit F2 to load the default setting and continue.
so try F1 or F2 when you reach code 85 and see if it progress further.

Have you checked your bios battery to make sure it's not low or dead. I've had many many boards that would either act dead or behave really weird with a low/dead/missing bios battery.

As stated, the caps look suspect based on the quality of pics. and keep in mind these ecs boards while somewhat versatile, they were considered throw away boards. If memory serves me, I got mine for "free" at the local Fry's on a combo deal. I had a barton overclocked on one using 2 strands of wire from an ethernet cable, and the fact you can use sd or ddr ram is kinda cool too.

Agree with Repo Man11 psu might be an issue.

CMOS battery is brand new... I've tried a couple now.

Good catch on the capacitor. I'm not that calibrated but I was assuming it wasn't bad enough yet.

Appreciate that this was a "throw-away" motherboard, but from what I have found it kind of feels like they all were back then. I know I just ruthlessly moved on to new hardware back in the day...

I've got another motherboard on the way. Hopefully I have more success with that - at the very least it will be an opportunity for more experimenting and maybe even soldering.

If the power draw on the +5 is too much for this power supply, you might be able to get it to POST with a basic PCI video card (watch the linked video if you didn't). If you have one on hand, I'd try it. The K7S5A is a perfectly good motherboard, even if it was a budget one at the time, and it is worth recapping.

I had a K7S5A with exact the same issue and for me it was the capacitors. They didn't even look bad. On the other hand I had a MSI K8T Neo board with all CPU VRM caps bulging that was working 100% fine... Another issue I had was a corrupted BIOS. I had to reflash using an external programmer and voila the board came back to life.

All the green crapacitors should get replaced, even if they _seem_ to be o.k.

I have one of those mainboards.
replaced all the caps on it.
fried a cpu.
verified cpu voltage rails, measured the correct voltage.
fried another cpu.
stuck the board in my pile 'for parts' pile.

I have the exact same board and my board also started to freeze up with random lock ups.
But, all the green capacitors on my board are bulging so it's clearly time for a recap.
I'm confident that after a recap the board should work again.
I happen to have a nice Athlon Thunderbird 1400 that I want to pair with that board.

Karbist wrote on 2024-04-30, 16:04:

I did some tests on my gigabyte 7zx and code 85 is related to cmos setting is not saved and when you power up the board, it halts on this code and asks you to hit F1 to enter the bios settings or hit F2 to load the default setting and continue.
so try F1 or F2 when you reach code 85 and see if it progress further.

This comment sent me down an interesting path last night. The computer gets to POST code 85 with no display, but I can get it to progress by hitting F1/F2... still without display.

This got me wondering if it could be an issue with the AGP... sure enough if you Google something along those lines there is no end of discussion of this exact issue from 20+ years ago! For example: https://forums.anandtech.com/threads/k7s5a-wont-boot.993850/

This includes some discussion about the board sometimes not working in the case... which could explain why it worked for the previous owner. I'm headed out of town this evening so it may be a while before I can continue troubleshooting, but I will be trying to run it out of the case. If I had a PCI graphics card that would also be an interesting test.

Of course, it could just all be because of the caps.

I also have a K7S5A motherboard, though I never really did anything with it (was a freebie from a PC repair shop about to throw it away), other than finally figuring out how to make it POST several years ago. In my case, the board would NOT POST with any DDR(1) RAM of any kind. I tried high density & low density modules of various capacities, and result was the same - none of them got the board to POST. Finally, I decided to try some SDRAM. Miraculously, the board appeared to work fine with that. Thought it must be a fluke incident, so tried with the DDR RAM again, but same thing - no POST. Interestingly enough, I initially thought the CPU I used was the problem, since it was a Duron Applebred 1400 (Thoroughbred B) core and perhaps too new for the board. But that wasn't the case - with the SDRAM, the motherboard booted fine with the CPU.

Unfortunately, I never did anything more with the board since then. I did check absolutely all of the small SMD components on the board to make sure nothing is out of the ordinary... and it wasn't - no chipped resistors or caps to cause the issue that I was seeing with the DDR RAM.

From what I've read online, some of these board can be extremely buggy with their original BIOS. If you have the means to program the BIOS externally to a newer version, perhaps that might resolve your issue?? Or not, IDK.

As for the caps: yes, you should change all of them. I see OST RLP series and G-Luxon LZ. The latter are pretty terrible... though sometime they are still OK, like they are on my board (not that I would leave them on there when I do get to making a build with that board.)

The bulging cap on the top of your board may or may not be the cause of your issues... though I suspect that it isn't, since that cap is on the 5V rail before the CPU VRM high side caps (separated by an inductor, so HF noise from CPU VRM shouldn't be making it back to the rest of the board.)

I have one here that I personally recap'd. Polys almost everywhere else aside from CPU VRM and a cap beside the AGP slot. Boots with both DDR and SDR.