Author Topic: Dell proprietary PSU repair [SOLVED] (Read 34122 times)

stj · « **Reply #25 on:** August 11, 2016, 07:26:19 pm »

if the fet blows,
you have to check *everything* related to the controller.

meter every resistor, and diode.
and look for burns on the controller i.c.

spilihps · « **Reply #26 on:** August 11, 2016, 07:44:56 pm »

Quote from: stj on August 11, 2016, 07:26:19 pm

if the fet blows,
you have to check *everything* related to the controller.

meter every resistor, and diode.
and look for burns on the controller i.c.

The controller is replaced, and some components surrounding it that also did not check out OK.

The thing is that measuring the voltage over the opto, directly when plugging it in, it jumps up a bit, and then shuts of. Probably some safety thing.
Now, does that rule out the primary side, or can it still be both sides?

stj · « **Reply #27 on:** August 11, 2016, 08:42:58 pm »

it could be the opto - i have had one that was bad

spilihps · « **Reply #28 on:** August 13, 2016, 04:01:25 pm »

Sorry, i forgot to mention in my earlier post, that i replaced all three optos, just to be sure. Eventhough they did check out in a test circuit

wblock · « **Reply #29 on:** August 13, 2016, 04:37:09 pm »

Quote from: spilihps on August 11, 2016, 04:19:09 pm

However the large blue one, checks OK with capacitance measurments, so i left it.

Electrolytics can fail and still show reasonable capacitance. An ESR check is the only way to really know.

spilihps · « **Reply #30 on:** August 13, 2016, 04:48:58 pm »

Quote from: wblock on August 13, 2016, 04:37:09 pm

Quote from: spilihps on August 11, 2016, 04:19:09 pm
However the large blue one, checks OK with capacitance measurments, so i left it.

Electrolytics can fail and still show reasonable capacitance. An ESR check is the only way to really know.

Thanks for your input!

Alright. I do not have access to a ESR-meter, but i may just have to get hold of one then

However, just to be sure we are not chasing the wrong part.

The thing that it for a breif second gives output to the Opto and then shuts of. Can this be because of this electrolytic? Feels like the safety circuit kicks in or something like that?

stj · « **Reply #31 on:** August 13, 2016, 07:21:57 pm »

from experience, you will *eventually* find some smd resistor that does not meter the same as it's markings or a bad smd diode.

when i was fixing the newer ones, it was a real pain in the ass.
http://www.badcaps.net/forum/showthread.php?t=50864

spilihps · « **Reply #32 on:** August 13, 2016, 09:56:00 pm »

Sorry, iam not following you?

stj · « **Reply #33 on:** August 13, 2016, 09:58:39 pm »

the link was an expample of how much damage can happen.

spilihps · « **Reply #34 on:** August 13, 2016, 10:14:51 pm »

Yeah that is almost exactly the same amount of damage that mine have,except only the main fet was shot..

So i wonder were to go from here

stj · « **Reply #35 on:** August 13, 2016, 10:18:57 pm »

if the fet shorted either high voltage pin to the gate pin then your testing all the resistors.

spilihps · « **Reply #36 on:** August 13, 2016, 10:22:04 pm »

The fet was shorted to all three(!) legs

Ive checked all the non-smd transistors. And i Went over the smds also, but only for opens since those were still in circuit.

spilihps · « **Reply #37 on:** August 22, 2016, 04:33:57 pm »

Hello again everyone!

Well, i invested in an ESR-meter. (EVB)
And it arrived today.

But, it seems like the suspected caps, that are 102k, and 103M and such, are not fit for testing like this. Ive tested them out, and it just "-" so i thought, great, their bad.
However, i had 8 brand new 102k laying around so i tested them also. Same thing with them. And i did double-check with my DMM, and sure enough they measure OL.. Even though they test fine in capacitance measurement..
So it was kind of a bad investment at least for this project.

Dont know how to go further with this now..

wraper · « **Reply #38 on:** August 22, 2016, 04:55:37 pm »

ESR meters are for testing electrolytic capacitors. Ceramic and film capacitors don't need for ESR to be checked. Also, below about 0.5-1 uF you won't be able to check ESR anyway. For checking such capacitors, measuring capacitance and checking if they are not leaky (checking DC resistance, should measure like open) is completely enough.

spilihps · « **Reply #39 on:** August 22, 2016, 05:05:25 pm »

Thanks wraper.

In the previous posts, it seemed like i needed to check these caps also. But no problem. I will probably have use for this handy ESR-meter later on anyway.

However, i really dont know were to go from here now..

stj · « **Reply #40 on:** August 22, 2016, 06:08:05 pm »

check all the smd resistors with a meter set to ohms setting.

wblock · « **Reply #41 on:** August 23, 2016, 01:29:24 am »

Quote from: spilihps on August 22, 2016, 05:05:25 pm

Thanks wraper.

In the previous posts, it seemed like i needed to check these caps also. But no problem. I will probably have use for this handy ESR-meter later on anyway.

However, i really dont know were to go from here now..

Check all the electrolytics on that board.

spilihps · « **Reply #42 on:** August 23, 2016, 11:46:29 am »

Hello,

So im back from checking the electrolytics, (with my new handy ESR-meter) and they all seem to be within spec, on both primary and secondary.

So i checked all the smds and also the "regular" resistors, they are all good. And for a while ago, when i replaced the PFC-chip, i had that "daughterboard" out and then i know i checked all of them on that one too.
Now, it have a second "daughterboard" that have a power-management chip on it. I Have had that one out also, but i may need to yank that out again, since im not 100% sure ive checked all on that one, as i am with the pfc-board. I think i did.
That one is on the secondary though.

spilihps · « **Reply #43 on:** August 23, 2016, 02:48:51 pm »

So ive yanked out the board with the WT7507 on it.

All the resistor tests OK, also the transistors pass diode-test, likewise the regular diodes.
However, with the ESR, ive found that three of the very small electrolytics (16v 22uF) gets around 8-10ohms resistance. This is way up it seems. The charts say it 0.8 on those.
I have no idea if those even could make this fault?

stj · « **Reply #44 on:** August 23, 2016, 04:42:29 pm »

they are bad, and they are obviously needed.

spilihps · « **Reply #45 on:** August 25, 2016, 04:50:47 pm »

Yep, replaced those.

Still the same fault.

So, both "daughterboards" caps, and resistors are checked. All the mainboards resistors and caps are checked.

Now i really have no clue what to do next..

wraper · « **Reply #46 on:** August 25, 2016, 05:43:33 pm »

Quote from: spilihps on August 23, 2016, 02:48:51 pm

However, with the ESR, ive found that three of the very small electrolytics (16v 22uF) gets around 8-10ohms resistance. This is way up it seems. The charts say it 0.8 on those.

If those are of extra small size, then such ESR is likely OK for them. 0.8 is a bit too low for 22uF 16V, expect up to a few ohms for such.

stj · « **Reply #47 on:** August 25, 2016, 06:34:13 pm »

they are low esr caps.

spilihps · « **Reply #48 on:** August 25, 2016, 06:53:52 pm »

Well, no problem.. Those were a longshot anyway.

Any tips or ideas on moving forward on this is appreciated..

It would be great to atleast confirm what specific part of the PSU the problem lies?

wraper · « **Reply #49 on:** August 26, 2016, 05:13:30 pm »

Quote from: stj on August 25, 2016, 06:34:13 pm

they are low esr caps.

For what reason they should be? They are not filtering any of output power rails, nor experience any high ripple current.


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Author Topic: Dell proprietary PSU repair [SOLVED] (Read 34122 times)

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