Repair HP Z420 power supply

[pr0cess0r]

Hello, my Z420 enter a loop when i try to turn it spin the fans then click and start over in a loop.

I heated the power supply with a air dryer and it started and working perfectly.

I think that maybe its only a small startup capacitor that need to be replaced.

What information or pictures are needed to get your help?

[pr0cess0r]

Re: Rair HP Z420 power supply

here are somes picture. i see a cheap capacitor near the lm339an maube its just this one?

[Quaddro]

Re: Rair HP Z420 power supply

Delta usually make a solid solder job.
So cracked solder, mmmm, there's only little chance of it.

If psu entering loop state, that's 75% mean, the supervisor ic is damage.
Primary is okay, secondary is okay, but the supervisor ic think there's something wrong.
So it's cancel the on state and change it to off state, but because of sequence of command is not complete, then it's try to turn on again.
So, you have a infinite loop state.

Reheat, well, some ic react with heat and works normal temporarily after burn with heat.
But, it will fail again soon.

So, my suggestion.

1. well, try to refresh all solder
2. Try to check all components surround the supervisor ic.
3. and if it's not working, try to change the ic.

[pr0cess0r]

Re: Rair HP Z420 power supply

can it be the small cap near the supervisor IC??

[Quaddro]

Re: Rair HP Z420 power supply

Maybe, just try to replace it.
An esr meter will help to make sure the cap is the culprit or not.

[momaka]

Re: Rair HP Z420 power supply

The fact that the PSU works when warm but not when cold strongly suggests bad caps.

All non-Japanese caps should be replaced IMO, especially the small ones. Looks like you have some green caps - either Ltec, Lelon, or Taicon. Either way, none of those are exactly good brands, especially Ltec. Get rid of them all. The brown Chemicon (KZH) caps and few small Rubycon can stay - these are good Japanese brands.

[Wester547]

Re: Rair HP Z420 power supply

The fact that the PSU works when warm but not when cold strongly suggests bad caps.

All non-Japanese caps should be replaced IMO, especially the small ones. Looks like you have some green caps - either Ltec, Lelon, or Taicon. Either way, none of those are exactly good brands, especially Ltec. Get rid of them all. The brown Chemicon (KZH) caps and few small Rubycon can stay - these are good Japanese brands.

The light green capacitors are actually Taicon. I don’t see any LTEC or Lelon in the PSU (Lelon is actually worse than LTEC ), but I do see what may be a black Samxon GK? And if that’s the case replacing it may be a good idea as GK and GF are not good series. Since the PSU is acting up, a full recap wouldn’t hurt regardless of brand. You could argue Taicon is a bad brand just on the basis of being Taiwanese, and since Nichicon only own 37% of them, but Taicon only had a couple failure prone series IIRC (the HD and HI series), both of which were very low impedance water-based series. Nichicon had a few years where they had an exceptionally bad batch of HM and HN series (and NCC with KZG and KZJ, for several years), so I don’t think it’s fair to say Taicon is of unacceptable quality when they’ve only had a couple bad series too.

As stated before me, it wouldn’t at least hurt to replace all the small capacitors and reflow any suspicious solder joints.

[pr0cess0r]

Re: Rair HP Z420 power supply

i replaced the samll taicon cpa on the primary side and it fixed it. I need to order cap to do a full recap because i replaced the taicon with a OST and dont know how lo g it will last.

[Wester547]

Re: Rair HP Z420 power supply

Good work.

I may have cried wolf and overestimated Taicon's quality, but IIRC these PSUs have the fan positioned as an intake fan at the front rather than an exhaust fan at the back, so they run a bit hot, and if it came out of a workstation that ran 24/7, that 5mm diameter capacitor could have been somewhat starved of airflow. The smallest caps do usually dry out first provided the larger caps aren't very stressed. And it's a Delta unit, whose soldering is usually very good, so I guess resoldering joints wasn't necessary in this case.

[pr0cess0r]

Re: Rair HP Z420 power supply

yes this coputer whas on 24/7 used like a server in a not very well ventilated closet! From your sugestion i will replace all small caps in this psu when i nhave some time!

Now i build my free PLEX server!

[momaka]

Re: Rair HP Z420 power supply

Since the PSU is acting up, a full recap wouldn't hurt regardless of brand.

Well, I doubt a complete full recap is needed - the Chemicon caps should be more than fine there. Same goes for any Rubycon. I mean, these caps will do 10+ years in a hot LCD monitor PSU without problem, so a PSU like this with active cooling (fan) should definitely have kept them fine. It's only the Chinese and Taiwanese brands that should never be trusted.

I find Taicon and OST (certain series anyways) are indeed a bit better than the rest. But you can still get the random failures with them that is typical for other low quality cap brands, like you saw in this case. So when you have a PSU that is acting up, replace all of the non-Japanese caps. Then worry about the rest later.

i replaced the samll taicon cpa on the primary side and it fixed it. I need to order cap to do a full recap because i replaced the taicon with a OST and dont know how lo g it will last.

Nice to hear it works now!
Yeah, no one knows how long those OST will last. Could be a month, could be a year, could be a decade.

[Quaddro]

Re: Rair HP Z420 power supply

The fact that the PSU works when warm but not when cold strongly suggests bad caps.

Wow..
Nice info..
Thanks, i never know about this thing.
A nice repair trick.

As far as i know, based on my experience with wt7520, loop always mean that welltrend is broken.
And i already fix 30+ psu with that symptom..

[momaka]

Re: Rair HP Z420 power supply

Wow..
Nice info..
Thanks, i never know about this thing.
A nice repair trick.

Lol, it's probably the oldest trick when it comes to bad caps.

I had a router way back that would not turn on after a power outage. If I took its power brick out in the sun for a few hours, it would turn ON without problems.

Then later I recapped the bugger and that was the end of my issues with it.

As far as i know, based on my experience with wt7520, loop always mean that welltrend is broken.
And i already fix 30+ psu with that symptom..

Interesting. So WT7520 is known to fail a lot?

[Quaddro]

Re: Rair HP Z420 power supply

Interesting. So WT7520 is known to fail a lot?

yes..
in my country, we have a brand called venom rx.
Cheap and old school design psu, but pretty famous due to sleeving cable and led fan..

And one of the type using wt7520 as the supervisor ic.

If it's not working and give infinite loop, then 99.9% due to broken wt7520.

I usually replace it with est7502 as the equivalent.

[momaka]

Re: Rair HP Z420 power supply

in my country, we have a brand called venom rx.
Cheap and old school design psu, but pretty famous due to sleeving cable and led fan..

And one of the type using wt7520 as the supervisor ic.

If it's not working and give infinite loop, then 99.9% due to broken wt7520.

I usually replace it with est7502 as the equivalent.

But the question is, is the WT7520 dying by itself or is something in the PSU killing it? And if not, perhaps the new est7502 IC has better tolerances and can "cope" with something in the circuit that is causing the WT7520 to trip up.

With Teapo caps everywhere, there's no telling who's causing more problems.

[Quaddro]

Re: Rair HP Z420 power supply

But the question is, is the WT7520 dying by itself or is something in the PSU killing it? And if not, perhaps the new est7502 IC has better tolerances and can "cope" with something in the circuit that is causing the WT7520 to trip up.

With Teapo caps everywhere, there's no telling who's causing more problems.

Well..at least while i check with my meter, both capacitance and esr value in every each that capacitor is pretty good..
At least while in off condition..

Unfortunately i don't have oscilloscope, so i can't measure the performance of capacitor while running.

[Shonky]

Re: Rair HP Z420 power supply

i replaced the samll taicon cpa on the primary side and it fixed it. I need to order cap to do a full recap because i replaced the taicon with a OST and dont know how lo g it will last.

Hey pr0cess0r,

Are you still around? Which cap specifically did you replace?

I have a supply doing the same thing. I reheated a few joints on the primary board. A couple of the green Taicon caps measured ok out of the primary board so I put them back in as I didn't have replacements. Supply did work for a bit but then after a short power down, went back to the cycling problem. So I think in general the supply is OK i.e. not a dead switcher or anything major.

Since removing/replacing the two on the primary board seemed to help temporarily (even though the seem good) I tried replacing with new 105C low ESR caps but no go.

I replaced the 10uF/25V almost underneath the large DC cap. and the 10uF/50V near the 16 pin IC (I think it's an LM3xx quad opamp). Sorry don't have the designators as it's screwed back together at the moment but I marked the ones I replaced on your picture.



Was it one of these you replaced?

Thanks

[Shonky]

Re: Rair HP Z420 power supply

...near the 16 pin IC...

Sorry, 14 pin IC.

Can't seem to edit posts here?

[Kb7aVdTcAa3p]

Re: Repair HP Z420 power supply

Hello,
Thanks for this thread!
My HP z420 (600W supply) displayed the same symptoms (boot loop).
When I found this thread I tried right away replacing the Caps.
The issue is gone, probably I will replace all of the caps once I have time.
I replaced the small caps on the primary board (same as Shonky) and the small 10µ/50V on what I think is the the primary side of the tranformers on the second board.