Question Wierd Behaviour with Small Case

[XircuitHed]

Hello folks, first post here:

I am working on a build for my mom. Standard home PC, nothing fancy, main constraints are desk space(width) and cost. So I got a vios s607 slim case that came with an SFX PSU (branded vios but obviously some 3rd party white-labeled crap). The case with PSU cost me under USD45. As you can imagine, cheaping out here might have been a mistake but this was the only slim case I could find where I am.

I added the following :

1. Intel Pentium Gold G5400 with stock cooler
2. Gigabyte H310M A 2.0
3. Kingston 240G M2 2280 SSD
4. Patriot DDR4 2x4GB 2400 CL17 RAM
5. HGST 2.5in SATA HDD 5400RPM 500Gb from an old laptop.

I put in 1-4 and everything worked fine.

I put in 5 (SATA HDD) two days ago and then the computer would not start. Forget boot, POST would not complete. I'd see fans spin, but the power LED would not come on and no POST beep, could not even get into bios. I switched sata cables, I switched HDDs, I switched power cables. nothing helped. Interestingly, I'd jiggle things around and it would work, computer would complete post, boot up and then I'd secure everything and put the cover back on and then it would not start again. If I closed it up with the computer running, it would work fine for as long as it was on, but I'd switch it off and when i'd switch on again then it would not complete post. It looked for all the world like a PSU issue, but then I kept the drive connected outside the case with the case open and it would work fine - and even a

[Mod edit to remove profanity. Remember that this is a family friendly Forum.]

PSU shouldn't overload at such low load. Every time I put things back in and the cover back on the same issue would recur.

I was about to call a broken mobo, but then i noticed scratches on the top of my psu case. The way this case is setup is the sata drive is secured in a pull-out frame that seats right above the PSU, and the screw heads that secure the SATA HDD to the frame were scratching the PSU. On a hunch, I grabbed some polyester sponge and put it between the sata hdd screws and the PSU case, closed it up and voila, the problem seems solved. 2 days multiple tests and computer starts up fine.

I cant understand why isolating the PSU case from the HDD mounting screws would solve anything. The entire chassis should be at PSU ground anyway. The HDD mounting holes should be at PSU ground. The only way this seems possible is if PSU ground and SATA ground are not the same thing, or if my chassis is not grounded through the PSU screws.
I've tested voltages and power when on using OCCT , HWinfo64 and also the Gigabyte tool, all voltage rails look rock solid. 12.24V, 5.2xV, 3.34xV

1. Does anyone have any hypothesis that could explain why isolating two screws was the answer?
2. before I isolated, I did tear down the entire build (except for the PSU) and redid everything. but everything was seated fine IMO. and it did the same thing anyway, just one time before I used the sponge.

Am i being an idiot and missing something obvious? This CPU is going to go to my mom who is a senior and depends on me for all tech support, so its in my own interest to make this build rock solid, and without being certain I understand what happened, I don't feel confident about this.

One thing I am considering is spending another US$50 on a silverstone sfx 300w psu. but want to know what everyone here thinks.

 

[Ralston18]

My thought is that the PSU case is not properly grounded.

Check for a voltage between PSU case and the slim case.

I.e., between the PSU and the HDD mounting screws.

Take a close look at the metal framing involved: some twist or sag could be allowing contact which is broken when you "insulate".

You may be able to tighten, loosen, or shift one component or another to break any contact and increase separation.

Also: do not leave those sponges in place - they will most likely dry out and crumble away with heat and time.

Then the problem will reoccur....

=====

Side note:

And you should consider a PSU with more wattage. 300 watts likely to be too low for the build.

Total up the component wattages and use high end values if a wattage range is provided.

Once totaled, add 25% more.

 

[XircuitHed]

Thanks Ralston, good advice. I opened it up and took a DVM to check voltages and resistances across the case. but everything checks out, PSU is at ground, chassis is at ground, pull out frame is at ground. HDD mounting screws are at ground. no stray voltages, no resistance between any of them. At this point I feel like all I should do is invoke occams razor - I probably did not have something properly seated and when i did the rebuild I did get it in securely. I have not messed with the sponge just yet, but I will look for something a little better before i finally hand this PC over.

Will update this thread when i have more info.