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Need advice on theses capacitors
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Need advice on theses capacitors
ludotex
Hello,

I just got a used virus B. At first it would not boot (blank screen and just LFOs LEDS lit), but after a factory reset it's now looking like it works and plays fine.

I opened it to look inside. Most of the capacitors have been replaced before.

These 2 look suspicious though, what do you think?
I am surprised the synth works with these 2 capacitors looking like this.
Probably a timed bomb no?
What about the SMDs around them?

Other than soldering and following instructions I am not very versed in electronics, hence my questions to you about these caps.



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cretaceousear
Caps look OK - the crud on the PCB will be from their predecessors. That could be removed with a bit of careful scraping. The caps have not been put in neatly, but unless they are bulging or leaking they are good.
ixtern
ludotex wrote:
Hello,

I just got a used virus B. At first it would not boot (blank screen and just LFOs LEDS lit), but after a factory reset it's now looking like it works and plays fine.

I opened it to look inside. Most of the capacitors have been replaced before.

These 2 look suspicious though, what do you think?
I am surprised the synth works with these 2 capacitors looking like this.
Probably a timed bomb no?
What about the SMDs around them?

Other than soldering and following instructions I am not very versed in electronics, hence my questions to you about these caps.
]

Those caps are rather not going to explode but may be dry because of leakage, having a fraction of initial capacity. Better to replace them, clean pcb carefully and look if corroded-then-cleaned paths needs to be repaired. Other parts should not be damaged apart from maybe some corrosion (clean them also).
[if caps were to be replaced, pcb should be clean and it isn't, so I rather think it is leakage from them on the pcb]
ludotex
Thanks for the replies.

What do you use for cleaning this kind of corrosion?
goom
90+% isopropyl alcohol and cotton swabs should work just fine.
mskala
I'd use water first and then alcohol - the electrolyte may not dissolve well in alcohol, but you do need the alcohol afterward to remove the water and any remaining crud that doesn't dissolve in water.
JakoGreyshire
That black cap on the left is probably soldered on the other side of the PCB, but it doesn't look like the solder made it all the way through the PCB. It should look like the other solder joints around it...

The holes in the PCB where parts go are called vias, right?
jorg
I agree the caps with crud under them need to go, and use the cleaning instructions posted above. I also agree the black one is not fully soldered in - touch that up and look for any similar ones.

Technically, the holes where parts go are called "holes." "Vias" are holes where no parts go; they are used to make connections between board layers.
djs
cretaceousear wrote:
Caps look OK - the crud on the PCB will be from their predecessors. That could be removed with a bit of careful scraping. The caps have not been put in neatly, but unless they are bulging or leaking they are good.


Just a general note- I agree with your analysis here, but I did have a cap once "blow downwards" where it looked ok from above and the side, but had a bunch of crud beneath it.
cretaceousear
djs wrote:
I agree with your analysis here, but I did have a cap once "blow downwards" where it looked ok from above and the side, but had a bunch of crud beneath it.

Ah yes Watson, but then the crud would be all over like brains in a Tarantino movie. (mixing ma metaphors there) hihi
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