I thought I had bad caps ... replaced board ... problem persists!

[lneville]

I have a Dell Precision 470 - a model notorious for having unreliable caps, and about 2 years ago I had a genuine "bad caps" experience, replaced the board and all was good for a long time.

So when recently I started getting exactly the same symptoms, I thought it must be bad caps again. The PC would reboot with no apparent cause in the Windows logs. At first the PC would be up for a whole day before restarting, but it rapidly became more frequent, and now I am lucky if it stays up for 2 mins.

I tried vaccuming the dust off the board, reseating all memory, cards etc and even swapped the graphics card and re-did the thermal paste between the CPU and the heat sink (although the BIOS doesn't reporting a CPU temperature issue). I examined the board and didn't see any bulging or leaking caps (as I had the first time), but I went ahead and replaced the board anyway.

I am still getting restarts though! Maybe they are less frequent than before, but still make the PC unusable.

So what component could account for this? The only things that are the same as before the board replacement are:

Xeon CPU
Memory
Power supply
VRM

Many thanks

[retiredcaps]

Re: I thought I had bad caps ... replaced board ... problem persists!

The only things that are the same as before the board replacement are:

Xeon CPU
Memory
Power supply
VRM

Check your power supply for bad caps. Chances are you have bloated caps causing unstable power to be sent to the motherboard.

If you have a multimeter, it is easy to check to see if you have stable voltages.

[Agent24]

Re: I thought I had bad caps ... replaced board ... problem persists!

Yeah I would say PSU too.

[lneville]

Re: I thought I had bad caps ... replaced board ... problem persists!

OK thanks. Getting replacement from eBay.

[Agent24]

Re: I thought I had bad caps ... replaced board ... problem persists!

Replacement PSU is pointless, they all have the same problem (rubbish capacitors)

Get new capacitors and fix the one you have.

[PCBONEZ]

Re: I thought I had bad caps ... replaced board ... problem persists!

PSU or KZG or KZJ.
.

[lneville]

Re: I thought I had bad caps ... replaced board ... problem persists!

Agent24 - OK I may open the PSU up and try some surgery on it.

Is there any danger of electrocution from capacitance inside the PSU?

[PCBONEZ]

Re: I thought I had bad caps ... replaced board ... problem persists!

Agent24 - OK I may open the PSU up and try some surgery on it.

Is there any danger of electrocution from capacitance inside the PSU?

From caps, only if it's broken...
The caps have a discharge path so unless the path is broke caps aren't a problem.
.
HOWEVER:
If it's plugged in to line power you can have almost 2x line voltage in there and on some models (probably most) the heatsinks are energized.
.

[severach]

Re: I thought I had bad caps ... replaced board ... problem persists!

Open one up and measure the voltage of where you're thinking of touching compared to the case. The numbers should convince you how important it is to not touch. Unlike your fingers, you can attach the probes and watch the voltage change as you do various things such as turn on, turn off, and unplug to get an idea of how long it takes to become safe to touch.

Be sure to measure the AC and DC of the primary heat sink, the DC voltage of the large primary caps, and the DC voltage of both primary caps together.