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!

 

[f825_633]

fyi@repair.org wrote:

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!

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

 

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

 

[me]

fyi@repair.org wrote in news:M5Wdnd-EMZr7ovPUnZ2dnUVZ_uidnZ2d@giganews.com:

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

Maybe a bad back light inverter...


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

I must check into this further.

Thanks

 

[Clint Sharp]

In message <GYWdnTsxxeBk6fPUnZ2dnUVZ_jSdnZ2d@giganews.com>,
fyi@repair.org writes

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

I must check into this further.

Thanks
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

 

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!