attempt to repair power supply board

[ryn0909]

This is a continuance from my last post---> https://www.badcaps.net/forum/showthread.php?t=66677

Hp f2105 monitor with a dead power supply board. id like to repair it myself instead of replacing with a different one. I like the challenge of learning something new that interests me.

i decided to do some voltage reading comparison between a good working monitor, that was given to me and the one that i have that doesnt work. I have found an issue with mine but im not sure what to make of it. Checking the voltage at F851 and F852 the voltage fluctuates between 10vdc and 14vdc. the voltage at the same locations (F851 & F852) , on the good monitor, is a steady 18.98vdc any help is greatly appreciated.

[gabik111]

Re: attempt to repair power supply board

First of all get the schematic. It will be much much easier when you have a diagram of faulty device.
What is the board number of power supply? I couldn't find on the pictures.

[ryn0909]

Re: attempt to repair power supply board

board number is 4H.L1S02.A21 im searching for a schematic as we speak, so far no luck yet.

here as some pics of the board

[R_J]

Re: attempt to repair power supply board

If you can't find a schematic, provide very good high res. straight on pictures of both sides of the board, that way we can follow the traces and "maybe" help with the repair.
We can't trace the circuit with only top views.
Have you changed the small elecrolytics like c606 c611?

[ryn0909]

Re: attempt to repair power supply board

ok im working on the images as we speak ill post asap


im still trying to get a schematic for it but hp isnt wanting to cough it up

[ryn0909]

Re: attempt to repair power supply board

here are some pics let me know if u need more

[Dumah Brazorf]

Re: attempt to repair power supply board

Are you measuring that voltages with all other boards connected?
What if inverter and audio boards disconnected?

[ryn0909]

Re: attempt to repair power supply board

good question.... i dont exactly remember. ill take the measurement again and report back. ill do that rite now

[ryn0909]

Re: attempt to repair power supply board

Are you measuring that voltages with all other boards connected?
What if inverter and audio boards disconnected?

ok well after hooking it back up with all boards connected, i checked the voltage and it was fluctuating between 10vdc and 14vdc. i unplugged each board 1 by 1 and when i unplugged the logic interface board, the voltage stabilized at 18.98vdc. there was no change with any of the other boards plugged or unplugged

[Dumah Brazorf]

Re: attempt to repair power supply board

Well, let's have a look at the logic board.

[ryn0909]

Re: attempt to repair power supply board

Well, let's have a look at the logic board.

i know for certain that the issue is in the power supply board because when i attach the board from my other monitor (same model) everything works fine. i just now took measurements at the connector on the power supply board (cn702) that connects to the logic board see attached pic

[Dumah Brazorf]

Re: attempt to repair power supply board

I think you caused some damage working on it.
I see several scratches on the pcb and a trace probably ripped near a cap.
Clean the board from all that dust/fur/hairs and check for continuity between solder points at the ends of all the traces that present scratches or you worked on.

[Dumah Brazorf]

Re: attempt to repair power supply board

Here the pads are gone. Make sure there's continuity between the soldering points of ic403 and the first component connected to that traces.
So again check all of your soldering for continuity.
I also see some solder between that diode and that resistor, check if it's ok on the other board.

[Dumah Brazorf]

Re: attempt to repair power supply board

What's that? Is there at least some solder on the central leg?
You're using too much heat and probably no flux, your solder pads/points are mostly destroyed.

If the solder point is destroyed jump wire to the nearest solder point.

[ryn0909]

Re: attempt to repair power supply board

yes there is continuity at the points of concern i made double sure of that. also the problem exsisted before i replaced the caps

[sam_sam_sam]

Re: attempt to repair power supply board

Either you are using to much or you are staining to long on those small pads

If you put heat on a pad and the solder does not flow to Desoldiering wick then get off of it and put new solder on the joint and try it again if that does not work use some soldering flux and try again or increase your heat a little bit


I hope this helps


I use a Desoldiering Gun which makes easier but you can have the same problem if you use to much heat or you stay on it to long or you put to much pressure on the tip can do the same thing

When I use the Desoldiering Gun I have the temperature set for 775* F but with this setting I am on the the soldering joint and off of it very quickly

Now for multilayer boards it gets a little trickier this is when I have to set it to 890* F
and I might have to leave on the there a little bit more for ground plains to begin to flow with small soldering joints I leave it there until it flows and get off it

I have also ran across some boards are just plain s**t and those I have setting at 650* F and sometimes you have have to leave there for a little bit more for the solder to flow I do not like working with these boards you can tell if it’s this type of board because if you have it set for 775*F and turns the area around the pad black or brown it’s probably one of those type board

[ryn0909]

Re: attempt to repair power supply board

thank you but the solder joints are fine, they dont look the best but they arent shorted and they do have continuity.

[Dumah Brazorf]

Re: attempt to repair power supply board

Could you measure the voltages at the connector on the good board?
And on the bad with the logic one disconnected.
Is C811 missing?

[R_J]

Re: attempt to repair power supply board

I'll ask again, did you replace the small elec. caps in the primary?

[ryn0909]

Re: attempt to repair power supply board

I'll ask again, did you replace the small elec. caps in the primary?

sorry about that, i totally missed that question. No i have not changed the small electrolytic caps on the primary