Preliminary test before recaping

[Gianni]

Hi all

I have a question about testing a board so I'm here to ask suggestion from experienced members.

Probably I will have to repair a QDI MOBO with a Athlon 1800. The problem is that sometimes it start correctly and sometimes it doesn't recognize the RAM and it emits some BEEP sound.
Probably it has some bad brands caps but I'm not sure about it.

My question is: if I solder good caps in parallel to the caps present on the board, can I have problems?
I want proceed in this way because I don't want to waste time replacing caps just to discover the problem is still there.
I believe this method can work, if the caps on the board are ruined (reduced uF and high ESR) I think that soldering good caps in parallel should solve the problem so next step will be to replace the old caps.

What do you think?
Do you see any contraindication?

Thanks
Gianni

[linuxguru]

Re: Preliminary test before recaping

If you have unpopulated cap locations on Vcore, you can populate a few and check if the problem goes away. Otherwise, it's too messy.

[Gianni]

Re: Preliminary test before recaping

Hi linuxguru, thanks for your answer.

I received yesterday the PC so today I have opened it: there are 3 free locations around CPU, I can try what you suggested.
All caps look good... but I know that only measuring their parameters you can be sure they are good.

I posted some pictures in a new thread because I can't identify caps manufacturers.

I hope to have time on Friday to work on this MOBO.

Ciao
Gianni

[Solder Boy]

Re: Preliminary test before recaping

Hi.. in order to do a proper job you really need an ESR meter to check the other caps. If the board still beeps, it means the board is still alive and worthy of a recapping job.

Personally I would just replace the bad caps and be done with it. By adding new caps into the parallel series you aren't getting rid of the original problem. The bad caps are still going to be there.

There isn't really many shortcuts when repairing boards.

[Gianni]

Re: Preliminary test before recaping

Hi Solder Boy

I agree with you, caps must be checked (with ESR meter) to know if they are good or not, even if they are not bulging or leaking.

I just want to connect caps in parallel to see if the board works correctly, if it recognize RAM and start all (10-15) times correctly. If this test is positive, I will remove all old caps and then I place the good caps.
As I do this job for small amount of money, I would like to save time and I want to be sure that recapping it is the right solution.
If I recap it and the problem is still present, I have to trash the board and spend time to remove the new caps unless I trash them too.
Last year I spent a lot of time on my second recap and at the end I had to trash the mobo because the problem didn't disappear.

I'm not going to solder the good caps in parallel to the bad caps as final solution , it is just a test before doing the job.

I have an ESR meter in my office... but I can't take it at home or test the board in my office, I can check caps after I have removed them.

I will post some pics about the PC case so you will understand why I have doubts about the problem

Ciao
Gianni

[lucky13]

Re: Preliminary test before recaping

Hi Solder Boy

I agree with you, caps must be checked (with ESR meter) to know if they are good or not, even if they are not bulging or leaking.

I just want to connect caps in parallel to see if the board works correctly, if it recognize RAM and start all (10-15) times correctly. If this test is positive, I will remove all old caps and then I place the good caps.


I'm not going to solder the good caps in parallel to the bad caps as final solution , it is just a test before doing the job.



Ciao
Gianni

Hello Gianni,

I like your idea! I think adding low esr caps in parallel to questionable caps should allow the board to be checked for further problem. If no further problem, then yank out those bad caps and recap properly.

I find myself not willing to give up on a board when I've spent time and money to recap it. Especially one that appears to have some life (more like in coma) but not dead.

I am going to get myself some of those polymer caps to use for your idea. Then I will try your idea and post back here wih my results for all to see.

[yanz]

Re: Preliminary test before recaping

Gianni, that trick is one of many "first step" that i often do before recapping a mobo (but it depends on the situation). It sometimes help the bad mobo that have problem to POST properly..
I dont recommend this for a beginner because they will unlikely be able to do the soldering neatly.

[Gianni]

Re: Preliminary test before recaping

@ lucky13 : let me know your results, I will try next time if I receive a board with serious problem (doesn't POST, doesn't load OS, restart continuously).

@ yanz

thanks for confirming my idea was not completely wrong and not, I'm not a beginner with soldering.
This time I have skipped this step because a lot of caps had small pads so it would have taken a lot of time to solder the caps properly so at the end I decided to replace them all. I was lucky, the MOBO became reliable again and I gave it back after some test (Mem86 etc...)

You are right when you say it is worth to make this test with MOBO that doesn't post; in this case even if it takes some time to solder caps in parallel, if nothing change, it takes less time to remove them instead of desolder them from original position.

Ciao
Gianni