HP dc7800 bad caps

[jakah]

I found this when I was troubleshooting a bunch of HP dc7800 machines in my computer lab that had started to behave strange; a bad OST cap close to the memory slots. The board has a mix of caps from Rubycon, Sanyo, some green ones where I can't read the brand, and one OST (and some labeled FL...is that a name of a brand or a particular series of one???).

I haven't recapped yet, but planning to. Anyone else seen bad caps in those machines?

Regards,
Jakob

[retiredcaps]

Re: HP dc7800 bad caps

some green ones where I can't read the brand, and one OST (and some labeled FL...is that a name of a brand or a particular series of one???).

FL are Panasonic FL (high quality caps). The "T" vent are Panasonic.

The light green ones may be ltec?

I also see the "mercedes benz" vent (brown caps). If they are UCC KZG, replace them. They can fail without bloating.

So that is at least 6 different brands of electrolytic caps. Sanyo, UCC, Panasonic, Rubycon, OST, ltec?. This is surprising for a company of HP's heritage.

[jakah]

Re: HP dc7800 bad caps

Thanks a lot for your answer! The brown "mercedes benz" caps are KZG indeed. I attached a photo of the green caps (the best my smartphone camera could do).

Besides the KZGs and the OST, what caps would you suggest replacing?

Jakob

[retiredcaps]

Re: HP dc7800 bad caps

I attached a photo of the green caps (the best my smartphone camera could do).

Besides the KZGs and the OST, what caps would you suggest replacing?

The light green ones are Lelon. Most would suggest you replace these as well.

I personally would not because my soldering iron isn't the best and thus desoldering caps off motherboards are difficult for me.

[GbreadMan]

Re: HP dc7800 bad caps

So that is at least 6 different brands of electrolytic caps. Sanyo, UCC, Panasonic, Rubycon, OST, ltec?. This is surprising for a company of HP's heritage.

Are those Sacon FZ's around the CPU?

I am working on an HP, too...they throw all sorts of brands on. I found GSC, Ltec, Nichicon HM, all the usual suspects were on there. It's one of their low-end cheap pavilions so it's not unexpected.

Dan

[retiredcaps]

Re: HP dc7800 bad caps

It's one of their low-end cheap pavilions so it's not unexpected.

I didn't realize this model was one of those SFF heat cookers until just now.

[c_hegge]

Re: HP dc7800 bad caps

The ones around the CPU are Chemi-con polies, they can stay.

[jakah]

Re: HP dc7800 bad caps

Thanks all for your replies! I took a picture of the polymer caps around the cpu.

Also, I forgot to say that the mobo is from a CMT (tower) version of the dc7800. Today, I'll have a look at my dc7900s to see if they also have this problem!

[jakah]

Re: HP dc7800 bad caps

So now it's time to order some caps from Topcat! My idea is to do the following replacements to see if that solves the issues (and if not, then replace all those Lelon caps aswell):
- replace the three KZG 470 uF 16V with three Nichicon HN 470 uF 16V
- replace the OST 1500 uF 6,3V with a Rubycon ZL 1500uF 6.3V

Will those caps be good replacements, or do you have other suggestions?

[c_hegge]

Re: HP dc7800 bad caps

My only concern is that the ZLs might have a higher ESR than the OST RLA. I'd use https://www.badcaps.net/store/produc...roducts_id=147 (Nichicon HZ 1500uF 6.3v), or if you're feeling adventurous, https://www.badcaps.net/store/produc...roducts_id=134 (Chemi-con PSC 1500uF 6.3v polys).

[jakah]

Re: HP dc7800 bad caps

Thanks for the advice! I ordered both Nichicons and some polies, so I can test both

[jakah]

Re: HP dc7800 bad caps

I recapped the board, and the system seems stable so far!

However, I just noticed that the fan of the PSU has given up. The machine is just a bit older than three years. Planned obsolescence...

[dumpystig]

Re: HP dc7800 bad caps

Sods law, just when you overcome one obstacle...
I've had a few HP setups over the years (the past 2 years I've owned a dc7700 CMT) and never had any probs with circuit components or hardware. In my experience I highly rate build quality and choice of hardware components. Maybe you're just a bit unlucky with your particular machine.

On the other hand it does piss me off with the limited function access in BIOS.

[jakah]

Re: HP dc7800 bad caps

Today, I checked my 15 other dc7800 I have in my computer lab, and all of them had a working fan, luckily! Hopefully only something with that particular machine, yes I have the same experience as you dumpystig. This model is the first one from HP I've seen problems with for a long time. I remember bad caps in some old S478 HP systems.

So now I'm about to order some caps for all those 15 machines. Unfortunately, they don't let me (easily) order stuff from companies outside Sweden, so I've been looking at Farnell. Unfortunately, they don't have the nichicon caps I ordered from Topcat.

So my question is, will this Panasonic FM capacitor serve as a replacement for the 1500 uF cap?:
http://se.farnell.com/panasonic/eeuf...0uf/dp/1848408

And this Panasonic FM a replacement for the 470 uF caps?
http://se.farnell.com/panasonic/eeuf...16v/dp/1219462

Or should I use some other series of Panasonic, or another brand?

Jakob

[retiredcaps]

Re: HP dc7800 bad caps

So my question is, will this Panasonic FM capacitor serve as a replacement for the 1500 uF cap?:
http://se.farnell.com/panasonic/eeuf...0uf/dp/1848408

The above link goes to a FC cap, not FM. FC is the entry level ESR cap and likely not suitable for motherboard. FM, might suffice depending on the original cap ripple and ESR values.

[jakah]

Re: HP dc7800 bad caps

Oh, sorry, here's the right link: http://se.farnell.com/panasonic/eeuf...-3v/dp/1219448

Farnell has FC, FK, FMs of 1500 uF. The FMs seem to have the lowest ESR, or am I reading those specs wrong? They also have Rubycons. What series should I pick there?

Thanks for all help!

[retiredcaps]

Re: HP dc7800 bad caps

Here is what to look for. More or same ripple. Lower or same ESR.

The original caps are OST RLA series. Datasheet at



1500uF, 6.3V = 2100 ripple and 15 mohm.

Panasonic FM specs are

1500uF, 6.3V = 2180 ripple and 19 mohm.

So the FM is very close to the original OST cap. Members here report that new Panasonic caps test lower than their rated spec when measured with an ESR meter.

So for me, I would go ahead and use FM given your ordering limitation in using a local supplier.

The Rubycon ZL has 1820 ripple and 23 mohm which is worse than the Panasonic FM.

You can do the same comparison for the KZG 470uF as an exercise.

[c_hegge]

Re: HP dc7800 bad caps

If you must use pannies from there, go with the FM. they are a downgrade from the originals (and may be physically larger), but they are the most likely to work.

[jakah]

Re: HP dc7800 bad caps

Thanks for that information! Now I know better what to look for.

For the 470 uF 16V caps, the only good option I found on Farnell was a Panasonic polymer cap:
http://se.farnell.com/nichicon/plg1c...16v/dp/1580601

Operating lifetime is a bit low (2000h). Why is that?

[retiredcaps]

Re: HP dc7800 bad caps

Thanks for that information! Now I know better what to look for.

For the 470 uF 16V caps, the only good option I found on Farnell was a Panasonic polymer cap:
http://se.farnell.com/nichicon/plg1c...16v/dp/1580601

Operating lifetime is a bit low (2000h). Why is that?

Use this

http://se.farnell.com/panasonic/eeuf...0uf/dp/1848388

It is Panasonic FM 470uF 25V. By going up in voltage, you get a bit lower ESR and and more ripple (30 mohm and 1560 ripple mA). That is then closer to the 25 mohm of the OST RLA 470uF 16V cap.

WRT to 2000 hours, see

https://www.badcaps.net/forum/showpo...30&postcount=7

And the 470uF 25V cap has 4,000 hour spec. The newer Panasonic FR series is equivalent to the FM series, but sometimes has better hours in some sizes.