Can ceramics go bad (Rebis EQ)?

[living sounds]

I recently aquired a Rebis RA 402 parametric dual channel EQ for cheap. It's quite well-build, works all right and unlike the 500-like modules the manufacturer made doesn't do much harm to the signal, there's hardly any high end attenuation with the pots set to zero. It doesn't sound as nice as some of my high end EQs though, the high end being somewhat sharp and grainy. It uses LF353N op amps, silver Siemens poly caps and Phillips electrolytics (or probably can tantalums).

So, I opened it with the intend of doing a little modding, and found all the small blue disk caps, looking - in size and shape - like ceramics and nominated with double digit values (like 47) to have some sort of dried liquid on their upper side. Looks like old battery acid or electrolytic fluid. They don't look like tantalums (drop shape), and there are no polarity markings on them. There re also a few (other?) ceramic caps with different colors shapes (typical ones I recognized) on the boards that don't suffer from this problem.

Anyone knows what this is about? Unfortunately I cannot make pictures currently.

Thanks!
Gregor

 

[analogguru]

....It uses LF353N op amps....

I would suggest that they are in reality 748´s (single op-amps).
Unit is running on 40V single supply (approx).
The circuit of each of the 4 bands is very similar to the RA 204.

The capacitors should be 4,7pF ceramics and they normally don´t go bad.  Some poor quality ceramics can be microphonic, but from the beginning.

analogguru

 

[living sounds]

Thanks! So what do you think that stuff on the caps is? It's on all of them in varying degrees. Can silver mica go bad? Or could this be some other type of cap?

I don't think the op amps are single ones, there aren't enough in there. I'll look into it again, will do some measurements when I've got the time.

 

[maxwall]

pics would be nice

 

[stickjam]

pics would be nice

Ceramics Gone Bad  ;D

 

[matta]

pics would be nice

Ceramics Gone Bad  ;D

Dude, I could not stop laughing for 5 straight minutes, oh my goodness that was FUNNY!

Matt

 

[living sounds]

pics would be nice

Yes, but I haven't got a camera capable of doing close-up shots.

 

[tommypiper]

Could be MOVs that got popped?

 

[wtmnmf]

There is a kind of wax-like coating on old ceramics that degrades with age and looks like what you are describing.  Can you scrape it off?  The stuff I'm thinking of scrapes off and reveals a part with no defects.

 

[living sounds]

There is a kind of wax-like coating on old ceramics that degrades with age and looks like what you are describing.  Can you scrape it off?  The stuff I'm thinking of scrapes off and reveals a part with no defects.

I'll look into it tomorrow, thanks!