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Old 10-19-2017, 02:06 PM   #1
BLinux
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Default Trying to repair a HP Z800 850W PSU by Delta

This is for my son's computer... got a really nice deal on a HP Z800 (12-core/48GB) for like $250 on eBay. It's been working great for a few months, but then started to randomly reset/reboot, and at times refuse to power on at all. When this happens, there's a audible "clicking" sound, like a relay switch sound. But, it's not consistent... some times the power supply works fine for weeks at a time. And then some times it runs into this resetting issue. Some times worse than others; one time it even failed it's own "BIST" (built-in self test) mechanism, which consists of pulling the PSU out, plugging the power cord in, and there's a LED that turns green if it passes. Most of the time, it passes this test, but some times it fails. Online posts have indicated this test can pass even if there's a problem as there's no load.

Doing my research online, I found this to be pretty common issue. Several posts claim due to bad capacitors. So I open up the PSU to see if I can find the problem. I can't find any visual signs. I'm attaching photos of I took to see if someone can point out something I missed.

I got myself a ESR meter, and I've been going through each capacitor one by one. So, far, I've gone through about half of them and haven't found any issues. Though, the Rubycon caps had some incredible ESR readings (0.001 ohms)....

Anyway, looking for suggestions...
Attached Images
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File Type: jpg IMG_20171018_233211.jpg (465.6 KB, 106 views)
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Old 10-19-2017, 05:06 PM   #2
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

if it's because of bad capacitor and no physical damage on it, the easiest trick, just blow heat through board.
You can use hairdryer for it.

First, blow it on the all capacitor in primary side.
Then try it.

Is the problem persist?
if it's not, then just change the capacitors on this side.

if the problem still persist, then blow the heat on the capacitor secondary side of your psu.
then check it.
If it's fix the psu, then replace "ALL" capacitor in secondary side.
If the problem still on there, then you should take your attention to the other component.

Last edited by Quaddro; 10-19-2017 at 05:07 PM..
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Old 10-19-2017, 05:30 PM   #3
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

Check those green Ltec in photo 3, one in the middle of 4 also i think.
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Old 10-19-2017, 07:10 PM   #4
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

Based on the datecode on the PCB I think that PSU is about 6 years old. That white or light tan block in the bottom right of pictures 1 and 2 is a relay. Several cycles after turning on the relay shorts out the two inrush thermistors. It allows the use of higher resistance thermistors to reduce inrush and then shorts them so they don't dissipate power and get hot during operation.

It may be that you are hearing the relay close and open, which suggests a possible problem in the Standby regulator circuit (the PSU is shutting down and trying to restart due to intermittent 5VSB and internal primary and secondary Vcc). Checking any small electrolytics on the primary side of that circuit would be a good idea. Those caps are stressed some, and if mediocre caps were used, 6 years might be about the kind of life one might expect.
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Last edited by PeteS in CA; 10-19-2017 at 07:17 PM..
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Old 10-20-2017, 12:47 AM   #5
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

Quote:
Originally Posted by Quaddro View Post
if it's because of bad capacitor and no physical damage on it, the easiest trick, just blow heat through board.
You can use hairdryer for it.

First, blow it on the all capacitor in primary side.
Then try it.

Is the problem persist?
if it's not, then just change the capacitors on this side.

if the problem still persist, then blow the heat on the capacitor secondary side of your psu.
then check it.
If it's fix the psu, then replace "ALL" capacitor in secondary side.
If the problem still on there, then you should take your attention to the other component.
The problem isn't that it fails often, rather, it works most of the time, and fails occasionally. So, what you're suggesting would be a way to get it to work when it is in failed mode, but what i need is a reliable way to trigger the fail at this point... it just happens randomly, which is really annoying.
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Old 10-20-2017, 12:50 AM   #6
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

Quote:
Originally Posted by diif View Post
Check those green Ltec in photo 3, one in the middle of 4 also i think.
those were some of the first I was suspicious about. i was wondering the same as PeteS below about the 5VSB, and I believe those Ltecs are connected to that... but my ESR meter said they were in pretty good shape, so I don't know...

Quote:
Originally Posted by PeteS in CA View Post
Based on the datecode on the PCB I think that PSU is about 6 years old. That white or light tan block in the bottom right of pictures 1 and 2 is a relay. Several cycles after turning on the relay shorts out the two inrush thermistors. It allows the use of higher resistance thermistors to reduce inrush and then shorts them so they don't dissipate power and get hot during operation.

It may be that you are hearing the relay close and open, which suggests a possible problem in the Standby regulator circuit (the PSU is shutting down and trying to restart due to intermittent 5VSB and internal primary and secondary Vcc). Checking any small electrolytics on the primary side of that circuit would be a good idea. Those caps are stressed some, and if mediocre caps were used, 6 years might be about the kind of life one might expect.
thanks for the advice... i'll be digging into that further...
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Old 10-21-2017, 06:42 PM   #7
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

If this were mine here is what I would do

What ESR reading did you get on caps with a UF value of 100 or less can you post your results
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These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
2 Hem Saw Computer Stack Board

All of these had CAPs POOF
All of the mosfet that are taken out by bad caps
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Old 10-21-2017, 09:52 PM   #8
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

Wow a whole lot of junk crap capacitors. when you see Crapxon on the primary side that's bad news. I highly doubt any of those electrolytics were in spec brand new. you can go through the trouble of fixing but is it worth risking frying your motherboard and hard drive. that PSU is landfill ready
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Old 10-22-2017, 10:17 AM   #9
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

Quote:
Originally Posted by CapSwapper View Post
Wow a whole lot of junk crap capacitors. when you see Crapxon on the primary side that's bad news. I highly doubt any of those electrolytics were in spec brand new. you can go through the trouble of fixing but is it worth risking frying your motherboard and hard drive. that PSU is landfill ready
Since the PSUs in the Z800 are a non-standard form factor it isn't like there are a whole lot of options, either repair that one or replace it with another that probably is the same design and same cap selection.

It is a Delta and looks well built aside from the mediocre caps, so it is probably worth a recap (especially since it looks like replacements are going for $100-$150 on ebay and likely have the same crappy caps).
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Old 10-22-2017, 09:42 PM   #10
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

the problem is junk caps stresses other components and causes them to fail or have intermittent failures. I got in the habit of changing out junk caps when the PSU is brand new. I still have units I bought 5 years ago that are still going strong
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Old 10-23-2017, 07:18 AM   #11
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

Quote:
Originally Posted by BLinux View Post
The problem isn't that it fails often, rather, it works most of the time, and fails occasionally. So, what you're suggesting would be a way to get it to work when it is in failed mode, but what i need is a reliable way to trigger the fail at this point... it just happens randomly, which is really annoying.
Try to refresh all the solder first.
Randomly failed can caused by cracked solder or bad contact.
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Old 10-23-2017, 10:49 PM   #12
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

Well, strangely enough... the PSU has been stable so for the last several days. I haven't replaced any components yet. As I was digging around, I did however find a huge glob of dust sitting between 2 legs of a MOSFET. I cleaned the whole PSU out more thoroughly with a air blow gun @ 75PSI. I don't know for sure if that huge dust ball had anything to do with the problem, but i guess we'll see.

Quote:
Originally Posted by sam_sam_sam View Post
If this were mine here is what I would do

What ESR reading did you get on caps with a UF value of 100 or less can you post your results
I didn't write them down, but there were in the single digit ohm range ones like the 22uF. If the problem returns, I'll make note to actually write down the readings; i was just comparing it with the chart and moving on.
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Old 11-15-2017, 03:39 PM   #13
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

oh well... the PSU worked for about 3 weeks this time and then started to act up again. today, it shutdown right in the middle of applying an update :-( .. that won't end well.

so, i guess i'll open it up again and re-check the caps and post the ESR values I get.

if I don't find any bad caps, what other types of failures would exhibit this type of behavior where it works for several weeks at a time, and then spontaneously shuts off and restarts?
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Old 11-15-2017, 05:04 PM   #14
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

Dry joints.
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Old 11-15-2017, 06:14 PM   #15
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

Quote:
Originally Posted by diif View Post
Dry joints.
by that, you mean bad solder joints, right? just confirming the terminology.

if that were the case, how does one go about finding these? are there any visual queues to look for? common places in a PSU where one might find them?
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Old 11-18-2017, 12:47 PM   #16
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

so had a little time today and opened up the PSU again. this PSU has some sort of self-test circuit, where if you connect the outlet power cable with the unit outside the computer, it will power on and a green LED will turn on steady if it passes the self-test. granted, this is done with no load. however, a few times when i've had this problem, the self test has resulted in a clicking and pulsating green LED instead of the usual steady green LED. some times it passes the self test, even when it is exhibiting the symptoms.

anyway, with that said, I opened up the PSU today and plugged it into wall power and started tapping around. there were a few instances where the green LED flickered, but i did not hear the usual click of the relay.

specifically, the LED flickered when I tapped:

1. the relay
2. the heatsinks
3. one of the smaller capacitors

not sure what the LED flickering really means. but i'm wondering if this is further indication of a bad solder joint?

i'll upload some pictures in hopes maybe someone can help me do a visual hunt for the problem?
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Old 11-18-2017, 05:02 PM   #17
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

Quote:
Originally Posted by CapSwapper View Post
the problem is junk caps stresses other components and causes them to fail or have intermittent failures. I got in the habit of changing out junk caps when the PSU is brand new. I still have units I bought 5 years ago that are still going strong
Quote:
Originally Posted by BLinux View Post
those were some of the first I was suspicious about. i was wondering the same as PeteS below about the 5VSB, and I believe those Ltecs are connected to that... but my ESR meter said they were in pretty good shape, so I don't know...


thanks for the advice... i'll be digging into that further...

Here is something you should try when checking these caps put them in front of air conditioning vent for about a minute then check the ESR reading then hold them in your hand for minute and recheck the ESR reading if varies more than 10% or if it comes close to 10% I would replace all

I have done this test on brand new caps and the reading might varies a few points .05 or less

This is how I found a problem with one of the machines controllers at work
It would act some time when it would be a little cooler out side

Last edited by sam_sam_sam; 11-18-2017 at 05:07 PM..
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Old 11-18-2017, 06:30 PM   #18
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

Hello BLinux,
There is a possibility that you may have a micro fracture on one of the tracks or an SMD component has a crack through it, though the track fault is more likely.
If you can check the PSU with its lid open and connected to the PC, you can try flexing the PCB with the handle of a screwdriver at various points to see if it fails at any time.
If it does fail in one section repeatedly, then you need to check the tracks on top as well as the bottom using a multi-meter set to low ohms.
Even though electro caps are the main weak point of PC power supplies, it doesn't mean that ALL faults with PSU's are associated with them.
Due to the intermittent nature of the problem, it does not seem to be heat related, but if you find that at any time the fault appeared when the overall weather was fairly hot, then there is a possibility it may be heat related. It could also be a track fracture that is expanding due to the extra external heat.
To confirm that it might be an external weather fault, you should try Quaddro's suggestion (Post#2), and blow heat into it while the lid is off the PSU and the PC running at the same time.
There is a good chance that the previous owner was aware of the problem to the point that he/she wasn't willing to have it fixed due to the intermittent nature of the fault. Therefore decided to sell it at a bargain price just to be rid of the headache.
Please let us know how you get on.
Good Luck!!!
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Relayer

Last edited by Relayer; 11-18-2017 at 06:40 PM..
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Old 11-19-2017, 02:09 AM   #19
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

ok, had some difficulty adding pictures earlier. they are attached here.
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Old 11-23-2017, 01:00 PM   #20
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Default Re: Trying to repair a HP Z800 850W PSU by Delta

you are going to keep having intermittent failures. the junk caps screwed up a component somewhere. since it proprietary HP junk I would find another one and change the caps before plugging it up. I've worked with these type of PSU's before and the Cisco PSU's have all Nichicon caps. HP went the cheap junk route to make more money
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