I thought I had repaired this Dell W3000's power supply , but
after about 20-30 minutes the power light goes out (no video or audio)
and the power light comes back on (sound and video returns for a sec.).
IOW, the power goes off and then back on. Over and over again with a few
seconds in between.

All the voltages appear to be correct. I'm just not sure if it's the power
supply or
logic board. I replaced the bridge Rect.(it was shorted), 20N60 Transistor
(shorted), Controller IC (shorted). and a couple of
Schottky Diodes. This could be heat related.

Any help or direction on this would great!!!!

TIA

On Fri, 8 Aug 2008 22:52:43 GMT, put finger to keyboard
and composed:

I thought I had repaired this Dell W3000's power supply , but
after about 20-30 minutes the power light goes out (no video or audio)
and the power light comes back on (sound and video returns for a sec.).
IOW, the power goes off and then back on. Over and over again with a few
seconds in between.

All the voltages appear to be correct. I'm just not sure if it's the power
supply or
logic board. I replaced the bridge Rect.(it was shorted), 20N60 Transistor
(shorted), Controller IC (shorted). and a couple of
Schottky Diodes. This could be heat related.

Any help or direction on this would great!!!!

TIA

No specific help, but some general ideas ...

Assuming the Schottky diodes are on the secondary side, then it might
pay to see what's connected to those rails.

Otherwise, if you think the uP may be shutting down the supply, then
try to locate a PS_ON pin.

If it's a thermal problem, then try to narrow it down with some spray
freeze and a hair dryer.

As a matter of course I'd check the ESR of all the electrolytic caps.

What is the part number of the PWM controller IC? Perhaps its
datasheet has an application circuit.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

The primary side controller is a MC33262PG.

Switching MOSFET: 20N60S5

The secondary schottky diodes (2): DSSK60-018A 180v 2X30A (I used two
DSSK60-015A 150v 2 x30A)
I could not find the exact replacement in stock.

One other schottky diode in secondary: 20CTQ150PBF (I ordered it but did not
replace it because it was not shorted)

Bridge Rect.: D5SBA80-7000 6A 800v (I used a D5SBA60 6A 600v)
At the time I ordered it, I could not find the exact replacement in stock.

I guess that could be part of the problem, but the replacements are very
close.
As you know, parts are hard to find.


Thanks for you help!

On Mon, 11 Aug 2008 14:46:34 GMT, put finger to
keyboard and composed:


The primary side controller is a MC33262PG.

That's a power factor correction controller:

http://www.onsemi.com/pub_link/Collateral/MC34262-D.PDF

There must be an additional PWM circuit to drive the chopper
transistor for the switchmode transformer.

Switching MOSFET: 20N60S5

The secondary schottky diodes (2): DSSK60-018A 180v 2X30A ...

Could it be that an excessive load on this particular rail is the root
cause of your problem?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

It also uses a least one ICE2AS01 controller IC.
It may have more, but I don't remember right off.

On Wed, 13 Aug 2008 14:59:06 GMT, put finger to
keyboard and composed:

It also uses a least one ICE2AS01 controller IC.
It may have more, but I don't remember right off.

That IC has its own internal overload protection but no external
on/off control. I was wondering whether the PSU had some control pin
that was being triggered by a fault condition on the logic board. I
notice that a lot of people are having power-up problems with your
particular model. One vendor is offering a replacement logic board as
a solution.

Here is the datasheet for the PWM controller IC:
http://datasheet.digchip.com/216/216...0-ICE2AS01.pdf

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

This unit does have powering on issues.

Can you tell me which vendor is offering a replacement?

Thanks

On Thu, 14 Aug 2008 03:51:35 GMT, put finger to
keyboard and composed:

This unit does have powering on issues.

Can you tell me which vendor is offering a replacement?

Thanks

This supplier is offering an exchange logic board for US$150:
http://www.lcdrepair.us/w3000-logic.html

The symptoms a

Power, Sound But No Picture
Have to press power button numerous times to get a picture
Power, Picture But no Audio Output

Not the same as yours, but it seems to be a common problem. I'd still
be looking around the power supply area, though, before taking a
chance on the logic board. If you do go for the board, I'd be keen to
know what the fix is.

The same supplier is also offering a PS for $120:
http://www.lcdrepair.us/w3000-Power.html

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On Thu, 14 Aug 2008 17:01:00 +1000, Franc Zabkar
wrote:

On Thu, 14 Aug 2008 03:51:35 GMT, put finger to
keyboard and composed:

This unit does have powering on issues.

Can you tell me which vendor is offering a replacement?

Thanks

This supplier is offering an exchange logic board for US$150:
http://www.lcdrepair.us/w3000-logic.html

The symptoms a

Power, Sound But No Picture
Have to press power button numerous times to get a picture
Power, Picture But no Audio Output

Not the same as yours, but it seems to be a common problem. I'd still
be looking around the power supply area, though, before taking a
chance on the logic board. If you do go for the board, I'd be keen to
know what the fix is.

The same supplier is also offering a PS for $120:
http://www.lcdrepair.us/w3000-Power.html

- Franc Zabkar
I have two W3000's and one of them has had the problem since day one.
It usually comes on first try, but often requires two tries. On one
occasion, it took 12 tries. Anyway, my guess (and I stress the word
guess) is that the backlight takes about 5 or 6 seconds to fire and
they have some logic that gives up if the backlight hasn't lit after a
certain amount of time. Unfortunately, some backlights takes just
about the same amount of time as the timer allows. If the timer
expires before it lights, the logic gives up and turns it off.
(Occasionally, it lights just as the logic turns it off so I see a
flash of picture). In other words, the only real problem is the
length of the timer. I have no idea if the timer is implemented in
firmware of some sort but it is frustrating to know a simple change of
a timer could fix the whole problem. My other W3000 (a year older and
therefore a lot more expensive has never failed once.) The problem
one was purchased "on sale" right before they stopped making them.
Hmmm.

...Pat

On Thu, 14 Aug 2008 12:40:57 -0400, greenpjs put
finger to keyboard and composed:

I have two W3000's and one of them has had the problem since day one.
It usually comes on first try, but often requires two tries. On one
occasion, it took 12 tries. Anyway, my guess (and I stress the word
guess) is that the backlight takes about 5 or 6 seconds to fire and
they have some logic that gives up if the backlight hasn't lit after a
certain amount of time. Unfortunately, some backlights takes just
about the same amount of time as the timer allows. If the timer
expires before it lights, the logic gives up and turns it off.
(Occasionally, it lights just as the logic turns it off so I see a
flash of picture). In other words, the only real problem is the
length of the timer. I have no idea if the timer is implemented in
firmware of some sort but it is frustrating to know a simple change of
a timer could fix the whole problem. My other W3000 (a year older and
therefore a lot more expensive has never failed once.) The problem
one was purchased "on sale" right before they stopped making them.
Hmmm.

...Pat

I notice that some (most?) lamp controller ICs have a timing capacitor
that is set to charge up to some trigger point in one second or so. If
the feedback voltage from the lamp's current sense resistor does not
reach 3V within that time, then the lamp controller shuts down. I
suspect that the "fix" in this case would be to increase the value of
the timing cap. Having said that, I can't see how a logic board swap
would cure such a problem, unless the uP was able to detect the lamp
in some way. It may be worthwhile to identify the functions of the
pins in the harness between the logic board and the inverter/PSU, or
at least to identify the lamp controller chip and study the
application circuit in its datasheet.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.