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B951Ui-2HnD Board repair

Posted: Thu Jan 14, 2021 1:13 am
by lasagna
Hi everyone.

I have a RB951Ui-2HnD that stopped working a few years ago, most probably because of rain damage. Anyway, I have some time now and decided to give it a go to repair the board. First thing I noticed was two capacitors that weren't working, so I decided to start with them.

Problem is... Removing the older ones was a hell of a hard job. It simply wouldn't come out. But I managed to do it. But because I had to use too much force I may have damaged that area of one of them. Ill post a picture here later.

So, i tested the voltage coming into those areas. I get 3.3v into one of them but nothing on the next one.

Long story short, anybody has any experience repairing these boards? I google a lot and couldn't find anything related to this.



Image

Re: B951Ui-2HnD Board repair

Posted: Thu Jan 14, 2021 11:45 am
by jebz
Problem is... Removing the older ones was a hell of a hard job. It simply wouldn't come out. But I managed to do it. But because I had to use too much force I may have damaged that area of one of them. Ill post a picture here later.

So, i tested the voltage coming into those areas. I get 3.3v into one of them but nothing on the next one.

Long story short, anybody has any experience repairing these boards? I google a lot and couldn't find anything related to this.
.
The capacitors generally have a good connection to a large ground plane of copper PCB. This needs moderate power in your desoldering tool to effectively heat the solder completely. If you pull the capacitors too hard without removing the solder or it being fully molten you will damage the feed through on the hole in the PCB. This can cause loss of signal/power to the other layers.
I use a desoldering tool like -
https://www.wagneronline.com.au/sc7000z ... /55926/fl/

Re: B951Ui-2HnD Board repair

Posted: Thu Jan 14, 2021 4:29 pm
by r00t
Best way is to have both broken and working board on you desk at the same time, so you can measure on both and see what's working and what's not, comparing voltages at the various ICs. Then check all the voltages on capacitors. If one is missing, try to trace it on a PCB... if the trace is broken, you can just fix it by adding a mod wire.

If one of the DC-DC converter output voltages is missing, first check would be output of the switch chip to see if it still works. You may have damaged it somehow.
If you have an oscilloscope, you can also check switching regulators if they are doing something or not.
It's possible to use external lab PSU to power the board directly (supply 3.3V, 1.8V and other needed voltages you see on the capacitors on the working board) but you have to be really careful when doing that. If you don't have proper lab powersupply and are sure the switching regulators are blown (it's just better to desolder them if you suspect they may be faulty, as they may cause short to ground), don't do it.

Re: B951Ui-2HnD Board repair

Posted: Sun Jan 24, 2021 9:04 pm
by lasagna
Thanks everyone.

Any chance there is a schema of this board around?