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Dell W3000 power cycles (PS2008 IC)

I'm working on a Dell W3000. The power supply has an issue.

The power supply powers on and right as the back lights come on the green led goes out and then comes back on. It does this over and over again. It stays on about 5-6 seconds and then powers off and then powers back on. I checked all voltages and they seem to be within spec. except the 24v lines are about 20volts.

As i check the voltages, they do not seem to fuctuate with the on and off of the led on front.

IOW, the PS goes on then right as the back light starts to comes on the power supply shuts down. Even though the output voltages stay the same. If the PS shuts off shouldn't the voltages go down?

It also has a 8 pin dip with PS2008 (0332) that drives a K2674 transistor and I can't find a replacement anywhere! I not 100% sure its bad yet.

Any Ideas on this would be great!

Reply to
fyi
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Have a dig about for some dead capacitors with an ESR meter, around to 10uf mark.

Reply to
f825_633

Thanks for the info.

I did check all caps with a ESR meter. They all check good.

After checking all caps, where would you go from here?

TIA

Reply to
fyi

snipped-for-privacy@repair.org wrote in news:M5Wdnd-EMZr7ovPUnZ2dnUVZ snipped-for-privacy@giganews.com:

Maybe a bad back light inverter...

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Reply to
me

A know good power suppy works fine. So, it's not the inverter(s).

I must check into this further.

Thanks

Reply to
fyi

In message , snipped-for-privacy@repair.org writes

If you have a good PSU then you can check voltages, might be worth doing but I'd be checking resistors and small components by now, are you sure you checked *all* the electrolytics? Checked for shorts on the rectifier diodes? Just placign the 2 PSUs side by side and comparing resistances with a multimeter can be useful as well.

All assuming you don't have schematics etc.

--
Clint Sharp
Reply to
Clint Sharp

I have checked all Electrolytics and they showed to be good. One on the good PSU showed .75 esr and the same one on the bad PSU showed 1.00 (47 mfd @

35v(*)). I may replace it anyway.

I have compared the values between power supplies and they are the same (using the diode and ohms scale). I thought for sure I could find a difference somewhere but I haven't yet.

I have replaced many components and the unit did work. After about 30 mins it would start turning off and then back on. Now it will not show a picture and the screen stays off, except for the led on the front. I did find a transistor (c3198 replaced with c1815) that was shorted and replaced it. This transistor was in one of the feedback circuits. At first I thought it was a bad cap(*see above), because the esr meter showed low DSR. but it was a shorted transistor.

The wierd thing is all voltages check correct and do not change with the PSU power cycles (when the green led on the front goes off and then back on).

I will check the voltages on the good PSU and see what it does.

This PSU has 5v, s5v, 12v, 18v, 24v (marked as 24v, DVM shows 20v), 33v outputs. Also it has a pwr connection. PWR (2.93v) (I guess the logic board tells the PSU to power on with this one.) I was thinking one of these outputs would fluctuate when the led on the front goes out and then back on, but I was wrong.

The PSU was hit by a power surge. The surge took out the bridge rect. and the controller IC and Power Transistor (Primary). It also took out two of the big schottky diodes (secondary side). All were replaced.

I can't get a schematic on this as far as I know. A schematic would be great!

TIA!

Reply to
fyi

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