Need help finding a replacement resistor.

[Winston Chadwick]

I've been working on some H240AS-00 PSUs from the Dell Optiplex 790.
Apparently, it's made by HIPRO.
PCB is labeled Rev. 02

I've been seeing a failure that was reported in this thread.

The 1kV rated ceramic snubber cap (C52) blows and takes Q51, R25, and IC301 with it.

According to stj, who posted in the above thread, this failure can also kill various diodes and resistors around the MOSFET. Thankfully, this hasn't been the case for me yet. I was able to repair a similar H240 by replacing only C52, Q51, R25, and IC301 with parts from a working donor unit. It passed 48 hours of stress testing with Prime95 and is still running.

The original C52 is marked 681K 1KV. I assume I'll need a 680pF cap here. Based on stj's advice, I plan to replace C52 with a 2kV cap like this one on all of my H240s.

IC301 is marked CP012A. According to the posters in this thread, the CP012A is only available from 3rd party Chinese suppliers. I guess I'll be getting these from AliExpress.

Finding a replacement for R25 is the problem for me. It appears to be a .27 ohm resistor. I believe stj described this as a fusible resistor. Unfortunately, I am unable to find a .27 ohm fusible resistor. Does anyone know where I might find a suitable replacement for R25? What kind of power rating do I need?

I'm aware of the bulging output filter caps on the example used in the pictures. I've also included pics of a naked H240 board in case that helps anyone, but the naked board is not from the same PSU.

[stj]

Re: Need help finding a replacement resistor.

they are often refered to as flameproof resistors.

[Winston Chadwick]

Re: Need help finding a replacement resistor.

I was hoping it would be a simple misunderstanding. Thanks for your help.

If I go through Digikey, it looks like my choices are 1W or 3W.

I guess I'll get 3W rated resistors like this unless it's overkill.

[Gabriel]

Re: Need help finding a replacement resistor.

How many CP012A do you need ? I'm the guy who maked the thread you linked to and at work we dump still working Dell 990 and 9010 with this psu as we have a 3 year rule for replacing these.

I dumped ~10 working ones not long ago.....

[Winston Chadwick]

Re: Need help finding a replacement resistor.

How many CP012A do you need ? I'm the guy who maked the thread you linked to and at work we dump still working Dell 990 and 9010 with this psu as we have a 3 year rule for replacing these.

I dumped ~10 working ones not long ago.....

Eventually, I will probably need hundreds of CP012A ICs. The company I work for owns over 2,000 Optiplex 790 SFFs. I estimate that about a third of our 790s have an H240AS-00 installed. Many of those are Rev 04 boards where they used two 1kV snubber caps in parallel (I'm hoping these won't fail like the Rev 02 boards). That still leaves quite a number of rev 02 H240s.

However, I would like to get between 10-20 CP012A for my first purchase so that I can be sure that I can get the repair running smoothly before we go full swing.

Edit: To clarify, these PCs are remote. When they fail, they are shipped to us in operations. I can't repair all of the field units proactively, so I have to wait for them to fail. This is why I expect I'll need to do the full repair even though I plan to upgrade the snubber cap on all of the ones that I can get my hands on.

[stj]

Re: Need help finding a replacement resistor.

the CP012A's have glue under them so they dont come off very cleanly.

as for the resistor, try to match length and diameter


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actually, if your going to buy used chips, you may be saving a lot of time if you just buy the sub-boards with the chip & related parts on.

[Winston Chadwick]

Re: Need help finding a replacement resistor.

the CP012A's have glue under them so they dont come off very cleanly.

I noticed that when I tried to desolder them. Using hot air, it seemed like the circuit layer delaminated from the backboard as soon as the solder joints reflowed. There's still a bit of a bubble under both of the boards I worked on. The board I tested worked even after delamination, but I think I'll try Chip Quik next time I have to remove that IC.

as for the resistor, try to match length and diameter

The 3W that I linked above is much closer in dimension than the 1W I was looking at, so I'll go with the 3W.

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actually, if our going to buy used chips, you may be saving a lot of time if you just buy the sub-boards with the chip & related parts on.

Good idea. I hope Gabriel is able to sell me some of those little boards.

[Gabriel]

Re: Need help finding a replacement resistor.

I got 2 on my desk for dumping tomorrow and if I'm lucky the container has not been dumped there might be some there too.

I check tomorrow.

[stj]

Re: Need help finding a replacement resistor.

maybe Gabriel can sell you the resistors & fets too.

[Gabriel]

Re: Need help finding a replacement resistor.

Ok, on my desk I had one D240ES-01 from a 9010 i7 and one L255ES-00 from a 9020 i5 - as you can see the 9020 psu is 12V only as mb provides 5v for drives.

Did not have time to have a look in the container today but I will at first chance.

If you want parts from these thats no problem.

[Winston Chadwick]

Re: Need help finding a replacement resistor.

I've seen those PSUs from the 9020. I haven't opened one yet, but they are also found in the Optiplex 7020 SFFs that we use.

I know how much trouble it is to get parts off of those boards. You aren't planning on desoldering components are you?

I appreciate the offer but, I don't want to ask you to go through too much trouble especially considering I'm not doing this as a personal project.

We might be interested in just buying the entire PSUs if they're still working. Of course, I don't know how much it would cost to ship from Norway. Have these been recapped or do they still have the Elite, Ltec, Capxon, and Taicon caps?

[Gabriel]

Re: Need help finding a replacement resistor.

No, I'm not planning on keeping any parts on these for my self - if I had not seen this post they would have been in the container dump in a few days.
They are still working and have not been opened or recapped in any way, if you want me to desolder what you want thats no problem. I have a fr300 so it will not take much time.

Postage prices for you, US will be ' the rest of the world'.

Also,we have signed up for the new Dell 7040 sff and even if non of these have failed yet I'm planning to open a psu to have a look at the inside.
Not sure but I think it might be the same as the 9020 12v only version.

[Winston Chadwick]

Re: Need help finding a replacement resistor.

OK, thanks for the info. I sent this thread to my manager. He should be contacting you soon. Thanks again for the offer.

[Gabriel]

Re: Need help finding a replacement resistor.

Had a look in the container and found one more, it's a H240AS-01.