The old tired capacitors decided to finally give up?

Motherboard capacitors? Or which ones?

Yes, motherboard capacitors.

They seem to look fine at a glance -- not popped, not bulged. The entire motherboard looks really clean, almost like new. Or this doesn't indicate anything?
Don't have a tool to check their "capacitance" unfortunately.

Could I have screwed something up when isntalling the GPU and/or RAM? Or it's absolutely not related, and "after does not mean due to"?

lafoxxx wrote:

Remembered I have been using overclocking -- turned it off -- problem solved. Even memtest (Windows, All free memory) showed no issues. Literally everything works great without overclock.

Then don't overclock. People don't want to understand that overclocking can damage hardware. If you want more speed, install a faster CPU. Overclocking retro hardware just makes no sense. Back then, it was done to save money by getting more speed out of existing hardware. But today, we can just use faster hardware, since it's cheap and readily available.

lafoxxx wrote:

Then the PSU failed almost immediately

The main culprit here, partial malfunctions on the motherboard.
You'll need another socket 370 board to test this theory.

derSammler wrote:

But today, we can just use faster hardware, since it's cheap and readily available.

Or he just wants to push that hardware to see what it can do. 😉 Overclocking is a legitimate & fun hobby.

Miphee wrote:

The main culprit here, partial malfunctions on the motherboard.

That was the other PSU -- some Powerman. After I replaced it with Sparkle there were no issues with overclocking before I replaced RAM.

Miphee wrote:

You'll need another socket 370 board to test this theory.

Found TUSL2-C for like 5 bucks, will try to get it.

Miphee wrote:

Or he just wants to push that hardware to see what it can do. 😉 Overclocking is a legitimate & fun hobby.

Pretty much this, yes -- now I'm just curious what exactly could have gone wrong. Especially considering even 2x128 ACE RAM lost overclocking stability.

I don't know what happened. Took motherboard out of the case to install new cooler, realized I'll better do it later (too scared to take the 370 bracket off at the moment -- can chop off something if the tool slips off) and put all the system together.

Problem solved, works without any issues with overclocking.

Maybe something was causing short-circuit, and I fixed it without even realising what I did?

Do you have any airflow in your case? Its possible the cpu was overheating. I believe Pentium III CPUs have thermal projection (power cut off at certain temps). Is the heatsink good and snug on the cpu? I know people tend to over bend the mounting arm for tualatins resulting in a loose heatsink

Doubtful you had a short if it would just randomly turn off, but not impossible

I only have one exhaust fan in the back, and the PSU fan (works as exhaust after I flipped it) right next to the CPU.

It should be pretty snug now I suppose -- after I moved the cooler a bit and pushed the mounting bracket a few times to see if it will jump off the socket mounts (it didn't, but that's another case -- 'taking off Socket 370 cooler').

Do you think I should install the rear case fan to the front instead? So the PSU fan would work as an exhaust

The CPU cooler I tried to install is a deadstock Thermaltake Volcano 7 by the way.

So, the problem reappeared.
Just tried to turn on PC after long wait (few months).
Before turning it on, I tried to connect the keyboard and Mouse through USB to PS/2 adapters to check if they will work (all 2 USB ports are occupied with mouse and keyboard at the moment, and I have no other options). These adapters didn't just slide easily -- had to use some force (but didn't break anything).
After making sure they don't work, decided to play some Delta Force, QUAKE2 and Unreal.
In Delta Force, main menu looked like it was covered by some repeating pattern made of red pixels. Alt-tab resolved the issue -- thought it's related to palette or something.
Then I tried launching Quake 2. After messing around with D-Tools settings (assign letter) to enable music, the PC just force rebooted.
Then I tried to play UnrealT, and the computer rebooted after a few minutes.
Then launched 3d WinBench -- and during some tests there was that red pattern like in Delta Force main menu. But it was fine. Then, after a few minutes, computer rebooted with same symptoms as did few months ago -- with these scary cracking sounds coming from PC Speaker.
Sometimes it will reboot even before Windows is loaded.
Disabled FSB overclocking -- problem persists

CPU temp doesn't get above 50 deg C according to BIOS (checked right after such reboot).

What's wrong? Could I accidentally bend motherboard or move some devices cards while connecting the PS/2 to USB adapters?
This time after reassembling didn't help.

Didin't try turning off GPU overclocking yet. Can it possible be overheating? But there was no such issue when the problem was resolved few months ago..
GPU PCB doesn't feel hot on touch (CPU too)

Update:

System assembled outside the case -- no issues during test time (5 minutes)
Put everything back into the case, case laying on side -- no issues.
Put case in vertical position -- problem occured immediately after powering on
Get PSU out of the case (on floor) no issues during test time (5 minutes)
Put PSU on top of the case -- problem occured immediately after powering on. Loose ATX power connector?
Reassemble PSU, put it into the case -- no issues during test time (5 minutes), but then sudden reboot with mentioned symptoms.

Bad PSU?

Sounds like a bad PSU to me. What's the manufacturer?

looking4awayout wrote on 2020-02-02, 14:54:

Sounds like a bad PSU to me. What's the manufacturer?

Sparkle Power Inc, circa 1998.
(:

Try another PSU if you can. The "rattling" sounds you hear might be the noise the PC speaker makes when it reboots. My RDD does the same too before it POSTs. It's a sort of soft "click" noise coming from the speaker, mine does it two or three times before POSTing. Maybe one of the rails of your PSU is no longer up to the task... I used to have a P&O (just another DEER rebrand) PSU that gave similar problems to yours. After replacing it I no longer had issues.

Yes, that rattling is definitely the PC speaker.
Will try the other PSU, thanks!

An old psu isn't something I'd trust, get a modern one, the p3 can get away with an old 250w and a modern 500w will have enough 5v amps for it

Installed slightly newer PSU (5 bucks) -- FSP Group Inc., 300 Watts.
Left PC turned on for 10+ hours, with UnrealT Botmatch (as Spectator) -- still powered on. So far so good.
Thanks!