Dell 2408WFPb / 2408WFP - No Power

[selldoor]

Re: Dell 2408WFPb / 2408WFP - No Power

My 2408 has just died, lasted 4 years and 10 months - shame I didn't have a 5 year warranty.....
I'm grateful to bicycle6228 for the schematic and suggestions so far, but swapping the KA431 hasn't worked for me.
Any other (polite) suggestions?
I'll get the scope out and have a poke around, but for now what voltage should be coming out of the PSU?
Thanks

What voltages do you get/ - are the pins labelled on either of the boards.

Welcome to the forum-
We can help a lot more if you please post good clear pictures of the 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

[faulkn_c]

Re: Dell 2408WFPb / 2408WFP - No Power

My 2408 has just died, lasted 4 years and 10 months - shame I didn't have a 5 year warranty.....
I'm grateful to bicycle6228 for the schematic and suggestions so far, but swapping the KA431 hasn't worked for me.
Any other (polite) suggestions?
I'll get the scope out and have a poke around, but for now what voltage should be coming out of the PSU?
Thanks

[jetadm123]

Re: Dell 2408WFPb / 2408WFP - No Power

Yes, it was very generous of you to share that schematic. However, I noticed that some of the resistors and diodes on the schematic do not have values associated with them. It would be great if someone that still has the board out can fill in those missing part numbers/values for future reference.

[bicycle6228]

Re: Dell 2408WFPb / 2408WFP - No Power

>Did you check every component to get to that one or ...
There was nothing obviously wrong via visual or resistance checks, and I could hear the ticking in T601, so I guessed the SMPS was trying to start, and I knew it wasn't an excessive load issue. I bought another 2408WFPb with a working power supply, put the two power supply boards side-by-side, focused some resistance checks on the feedback/isolator area and found differences associated w/ IC701. Out of circuit, the KA431 shunt regulator did not behave right per simple VOM checks. Swapped in a replacement KA431, and voila!
>Where in the world did you find the SCH?
It is hand drawn, by me, from scratch. Yeah, I'm retired and have many hours to kill.
>very hard to diagnose
Agreed; normally these switcher power supplies seem to fail with the usual culprits, but not this one.

[budm]

Re: Dell 2408WFPb / 2408WFP - No Power

Thanks for posting the SCH. Where in the world did you find the SCH?

[retiredcaps]

Re: Dell 2408WFPb / 2408WFP - No Power

Replacing the shunt regulator, IC701 in the attached schematic, fixed my Dell 2408WFPb power supply.

Thanks for reporting back. Every now and then we see a failed 431, but it is very hard to diagnose.

[selldoor]

Re: Dell 2408WFPb / 2408WFP - No Power

Well done bicycle6228 that is a good fix and the schematic will help others.
Did you check every component to get to that one or did you find it as a common failing somewhere?

[bicycle6228]

Re: Dell 2408WFPb / 2408WFP - No Power

Replacing the shunt regulator, IC701 in the attached schematic, fixed my Dell 2408WFPb power supply.

[retiredcaps]

Re: Dell 2408WFPb / 2408WFP - No Power

1) What is the DC voltage across that small cap (right of IC652)? Is it stable or fluctuating?
= 1.2 volts; very slightly fluctuating. (C716 this is)
c) Is there DC voltage on the Vcc pin? = Yes, ~ 7 to 8 volts.

Hmm, I haven't worked on a thread that started 1 year ago.

Try changing the startup cap first since it is easy to do. The SMPS needs roughly 12.8V on Vcc pin to startup properly as per page 7 of

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

[selldoor]

Re: Dell 2408WFPb / 2408WFP - No Power

Welcome to the forum- Bicycle6228
We can sometimes help a lot more if you post good clear pictures of the 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

It will be useful if you can say a bit about yourself - skills tools etc.

[bicycle6228]

Re: Dell 2408WFPb / 2408WFP - No Power

Ritalin:
I have a 2408WFP with the same no power issue, no bulged caps, shorted semi-conductors, burned components and nothing out of the ordinary.
What did you do to resolve your issue?

retiredcaps:
Answers to your questions posed to Ritalin, as pertains to the unit I have:
1) What is the DC voltage across that small cap (right of IC652)? Is it stable or fluctuating?
= 1.2 volts; very slightly fluctuating. (C716 this is)
2) IC601 is likely your SMPS chip.
a) What is the part number? = 1203P60
b) Find the datasheet. = done.
c) Is there DC voltage on the Vcc pin? = Yes, ~ 7 to 8 volts.
d) Is it stable or fluctuating? = Fluctuating between ~ 7 and 8 volts.

3) I assume you have mains x 1.414 DC voltage across the large filter cap? That is 120 V AC x 1.414 roughly 165 V DC? = Yes, ~ 165 volts.

Ideas / suggestions?

[retiredcaps]

Re: Dell 2408WFPb / 2408WFP - No Power

1) What is the DC voltage across that small cap (right of IC652)? Is it stable or fluctuating?

2) IC601 is likely your SMPS chip.

a) What is the part number?
b) Find the datasheet.
c) Is there DC voltage on the Vcc pin?
d) Is it stable or fluctuating?

3) I assume you have mains x 1.414 DC voltage across the large filter cap? That is 120 V AC x 1.414 roughly 165 V DC?

[Ritalin]

Greetings fellow badcap'ers... been awhile!

No bulged caps, nothing out of the ordinary, can't find any schematic to see if I'm getting the appropriate power. I did trace it to a transformer where there isn't any power going past it, but when I google it, nothing comes up.

On top it says... "1J.20319.001 / LTSJ

Thoughts/comments on where to start?