bad Dell 1504p monitor

[badcap400]

Hello all, I have a bad Dell 1504p monitor. It has no power led response whatsoever after the office had a power hit/surge. When I opened it up, I found a bad CapXon 100uf / 400v capacitor that had popped its top. Fast and easy, I figured, simple replacement. So I got a nice spare Nichicon unit in place, put the thing back together as nothing else appeared bad. However, I wasn't sure since many people have posted about problems with the daughterboards / mosfets on these. And, unfortunately, when I plugged it in, nothing happens.

So, I suppose that there are probably some bad diodes / fets on this thing; is it worth it to find a used power board (~20-30 bucks it seems) or should I just debug and replace the parts on the power board individually given that it took a power hit of some kind? BTW, it was running on a reasonably current (18 month old Monster) surge protected strip; the power hit damaged some other gear also, even gear running on power conditioners (although they were old gear as well).

[Davi.p]

Re: bad Dell 1504p monitor

What do you meean for "(18 month old Monster)"?
You probably have some bad compo on the primary side of the power circuitry, for example the diode bridge "rectifier", or worst case, a bad glass fuse accompanied by bad big mosfet, Rsense, maybe IC, connected discretes, maybe other.. check them..

[budm]

Re: bad Dell 1504p monitor

"(18 month old Monster) surge protected strip" It is an AC outlet strip with surge protection made by Monster Cable company.
How about upload good clear pictures of the boards?
What DCV do you have (measured between the two legs of that main filter cap) on that cap you replaced? It should have around 160~170VDC.

[badcap400]

Re: bad Dell 1504p monitor

Ok, I'll have to take some time out to get the pix. I might be able to get the old cap out of the trash still. And I'll have to buckle down to get those measurements, have to get the daily essentials out of the way (kids and all!). Should that main cap DCV be measured while powered on or powered off-disconnected. It's a pain to flip the powerboard out of the mount and still have power on.

[budm]

Re: bad Dell 1504p monitor

You will be making DCV measurement in the PRIMARY DEADLY side of the circuit, when making Voltage measurement, the board must be plugged into the AC outlet otherwise you will not have the Voltage to measure, when taking resistance reading, no power will be applied.
If you are not sure about safety precaution required when working in the primary side then I will suggest you not to do it.
The main filter cap 100uf 400VDC is laying on its side isn't it?

[badcap400]

Re: bad Dell 1504p monitor

Yes, the 400vdc is laying on its side. I'll be careful when measuring; it's just that the way the board is arranged in the unit, it's 1 of 3 separate boards and it has to be exposed in order to see the correct leads. Could be done from the back....just a bit of a pain because of the way of the whole arrangement is.
Actually, I could just pull the thing out entirely, separate it from everything else like the daughter and logic board, and then just power it while it's on my test bench by itself. Not having any load on it, wouldn't be a big deal?

[budm]

Re: bad Dell 1504p monitor

You can run the power supply/inverter board by itself to make sure it has DC outouts, it is an always ON power supply.

[badcap400]

Re: bad Dell 1504p monitor

Ok, so I pulled it apart again and measured the 400v cap legs at 165.1vdc. Will upload some pix in a bit. Maybe the transformers? The boards look ok in general; no burnt crud or darkened bits. Only the epoxy on the 400v cap was dark. Will post a pic of the bad cap too.

[badcap400]

Re: bad Dell 1504p monitor

ok, well, posted too soon. Looks like the inverter board has at least 1 probable bad transformer which was hidden by a plastic film cover. Here's the pix :

I took a shot of the edge of the inverter board where some translucent clear crud appears to have leaked from one of the transformers. In addition, on both transformers where there are 2 blue poly caps (HF224 / HC5012A), there's some dark brown discolored material between the caps and the transformers. Probably have to replace the whole thing as I wonder if the transistors on the other side are messed up.

On the power supply board, the big brown cap in the middle is the one I replaced which shows 165v.

Thoughts?

[budm]

Re: bad Dell 1504p monitor

"I took a shot of the edge of the inverter board where some translucent clear crud appears to have leaked from one of the transformers." Those are just flux.
What DCV do you have on the pins of the white connector CN2?

[badcap400]

Re: bad Dell 1504p monitor

ok, white pins from right to left (ie from the 1st pin next to the grey pin) 0v, 13.2v, 13.2v,13.2v, 13.2v, 9.7v