Dell 2408WFPb Monitor - No Power

[ForensicFixer]

Hi Guys

Back again this time with the above monitor. It displays no power symptoms and I can hear a clicking sound from the right most transformer T601. This sound is present with and without mainboard or backlight board connected.

The main capacitor reads 320v and there is no voltage on the cold side of the transformer.

IC601 is marked 1203P60 CPET 0823G
Pin6 is Vcc and voltages continually jump between 6 and 11 v.

Torpedo fuse F701 is open circuit.

The five cold side capacitors all gave reasonable readings although tested in circuit. I checked all obvious diodes for a short but found nothing.

My research found another thread on this monitor
https://www.badcaps.net/forum/showth...highlight=2408

however it was a different problem and it ended without conclusion. It does suggest though I'm looking for 23v out to the mainboard whilst on standby.

All help appreciated.

[retiredcaps]

Re: Dell 2408WFPb Monitor - No Power

IC601 is marked 1203P60 CPET 0823G
Pin6 is Vcc and voltages continually jump between 6 and 11 v.

Clicking/ticking and a fluctuating voltage on IC VCC suggests one or more of the following:

a) bad startup cap (maybe it is the one above the large filter cap)
b) bad SMPS IC
c) shorted component on the output side

[retiredcaps]

Re: Dell 2408WFPb Monitor - No Power

The SMPS IC needs 12.8V (typically) in order to start

http://pdf1.alldatasheet.net/datashe...I/1203P60.html

Change the startup cap, likely a 22uF or 47uF, and retest.

[ForensicFixer]

Re: Dell 2408WFPb Monitor - No Power

The suggested cap is marked C611 47uF 50v

I tested it out of circuit with an esr meter and it read 41.72uF and 0.56 ohm.

Do you think these values are suspect as specific valued parts can be difficult to trace locally?

[selldoor]

Re: Dell 2408WFPb Monitor - No Power

it is more than 10% out so id say change it. you could probably get away with
47uf 25v 68uf 25v or 68uf 50v if that helps

[ForensicFixer]

Re: Dell 2408WFPb Monitor - No Power

Thanks for the advice selldoor.

I replaced the cap with a new one of the same values.

Unfortunately the ticking is still there. The Vcc values also still moving from 6-11v

[selldoor]

Re: Dell 2408WFPb Monitor - No Power

Am I reading this wrong - The torpedo fuse is open? have you replaced it?

[ForensicFixer]

Re: Dell 2408WFPb Monitor - No Power

No I haven't replaced it. I had thought it being on the cold side, getting the hot side up and running would be the first step.

Its the fusable link between the schotty diodes and the mainboard power cable.

[jetadm123]

Re: Dell 2408WFPb Monitor - No Power

When vcc is going from 6-11V, is it jumping between the two numbers erractically? In other words, is it a gradual climb from 6 to 11 volts? Or is alternating between 6 and 11 volts?

[ForensicFixer]

Re: Dell 2408WFPb Monitor - No Power

Its a gradual climb with a lot of different readings in between.

I can get a resistance reading in both directions on D602 right of the power chip. Worth testing out of circuit?

[selldoor]

Re: Dell 2408WFPb Monitor - No Power

No I haven't replaced it. I had thought it being on the cold side, getting the hot side up and running would be the first step.

Its the fusable link between the schotty diodes and the mainboard power cable.

I dont know but am just wondering if the fuse is not fixed and the mainboard is not getting the voltage it needs to turn on the rest of the
voltages the PS is never going to start and the transformers will have nothing to drive so they will tick? Ive always wanted to use that.

[jetadm123]

Re: Dell 2408WFPb Monitor - No Power

There should be a mosfet connected to IC601. Please check it for shorts.

Also, do you have any idea why fuse F701 blew?

[ForensicFixer]

Re: Dell 2408WFPb Monitor - No Power

No idea why it blew, again don't know history of monitor.

With all boards connected I tested the output side of the fuse against ground. No shorts.

I tried a 24v bulb across the input side of fuse and ground in an attempt to present a load. On power up no change.

With all boards connected I tried the bulb in series across the fuse. On power up no change.

I checked the resistance across the primary winding of the transformer (solder points on two heavier tracks). Varying resistances were obtained but on most occassions it returned to open circuit.

Could the ticking be a symptom of failed primary winding?

[jetadm123]

Re: Dell 2408WFPb Monitor - No Power

The main transformer rarely fails. If there's a failure in the circuit, it more likely would be IC601.

[budm]

Re: Dell 2408WFPb Monitor - No Power

"With all boards connected I tested the output side of the fuse against ground. No shorts." What is the actual reading?

[ForensicFixer]

Re: Dell 2408WFPb Monitor - No Power

Reading starts at about 5 k ohms and climbs continously until out of range.

[ForensicFixer]

Re: Dell 2408WFPb Monitor - No Power

Eventually got a replacement power IC, IC 601. The clicking in the transformer remains. vcc on power ic still cycling from 5-11.8 or so however now there is voltage present in secondary section. It climbs to about 7v cycling in time with transformer clicking.

[selldoor]

Re: Dell 2408WFPb Monitor - No Power

Eventually got a replacement power IC, IC 601. The clicking in the transformer remains. vcc on power ic still cycling from 5-11.8 or so however now there is voltage present in secondary section. It climbs to about 7v cycling in time with transformer clicking.

Is that with all the boards and lamps connected

[ForensicFixer]

Re: Dell 2408WFPb Monitor - No Power

Yes with and without boards result is the same

[selldoor]

Re: Dell 2408WFPb Monitor - No Power

Ok - Can we get back to checking the voltage at the BIG cap
Carefully could be 400vdc set meter on 600vdc probe on each leg.
Tets it for a while - does it vary in time with ticking.

Can you post good clear picture of your boards
whole chassis, and then pictures of each board, front and back (in the same orientation) and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed

https://www.badcaps.net/forum/attach...7&d=1280167246

https://www.badcaps.net/forum/attach...6&d=1280167246

https://www.badcaps.net/forum/attach...4&d=1280167246