Re: 2465B SN 55xxx with TEST 05 FAIL 40

Chuck Harris
 

Hi Alex,

No, it is only 4 electrolytic capacitors. There are
a couple of tantalums, but leave them alone.

I mean put the board in the kitchen sink, put an inch
of warm to hot water in the sink, and a good squirt of
Dawn, or other detergent, and scrub the area around the
capacitors with a toothbrush. That is the only way I
have found that will really clean up the leaked electrolyte.

The electrolyte goes everywhere, and spreads as fumes, so
it will be both above and below the capacitors when they
are in the position they were in when the leak occurred.

If you must use alcohol, the 70% is best, though 50% would
be better. The electrolyte is a polar compound, and will
only dissolve in a polar solvent, like water. It will not
dissolve at all in 99% IPA, as there is no water, and alcohol
is not polar enough.

If you are worried about water infiltration into the pots,
you can put a piece of electrical tape over them, but I
haven't found that to be necessary. Shake the board dry,
and them put it in a convection oven. Nothing else will
be bothered by the water in the least bit.

Do not try to remove the capacitors as complete units if you
are going to use a single point soldering iron. That is
virtually guaranteed to destroy the board. Cut them apart.

-Chuck Harris


tekscopegroup@... wrote:

Hi Chuck,

Thank you for the very detailed input on the procedures. I've been reading up on this A5 board bad caps situation and have found similar good tips and information. In any case I hope the corrosion will not be that severe, but who knows given the symptoms. Guess I'll find out once the scope gets to me in what I hope will be about 2 weeks if all goes well. In any case I feel confident and have experience with SMD soldering using a fine tip conventional iron, which in this case would have been my choice as well to solder the new caps in to keep it simple. Also, if I am not wrong its really 5 SMD capacitors that need to be replaced on the A5 board, 4 on one side of the board, and another one on of the opposite corners I think?

Much appreciate the tips on heating cautions on the corroded pads, and definitively the sliding and not lifting the caps seems to make a lot of sense to further protect the board from heat delamination. Always a good thing to heed to the voice of experience, specially on Tek equipment this nice that would be a shame to ruin just because of a bad soldering technique.

One question comes to mind: when you say "wash it again with warm water and dish soap, and a tooth brush", once all the affected pads are clean and tinned, do you mean to wash the whole affected area and then just rinse off with water? Guess there are no parts nearby that can be damaged by the water. In other situations sometimes I had good results cleaning up residual corrosion on a board by using 70% alcohol and a soft toothbrush. I had to redo the cleaning/scrubbing process several times. Advantage of alcohol is that it will evaporate quickly, and much less water will be left behind in comparison to using dish soap and plain water throughout the cleaning process. But then of course this was a very different kind of board, only two layers, low density, etc. So if you could please elaborate a bit about the washing/rinsing procedure.

I've worked so far on three other Tek scopes, a 2247A, a 222, and a 2213A. The 2213A was my first scope repairing experience back around 2004-ish (power supply issues/bad T948 against all odds). Back then it took a me a while to troubleshoot that devilish inverter power supply, but with quite a bit of help from the amazing Dennis Cobley, and Dean Smith fedexing me a donated almost complete main board with the needed transformer, in the end that humble scope came back to life. But when it comes to a 2465B, which is a classic and must have, I consider myself a rookie at best. But I digress...

Thanks again.
-Alex

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