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JVC S-55 anomaly

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oldnotbold

Member
Recently purchased a JVC S-55 integrated amp and discovered tone controls had no effect. Purchased 100uF /35V caps for tone control board (C217&218 and C221&222) as per JVC Service Manual spec. in 'HiFi Engine', only to find that all those actually fitted are 220uF/35V.
Then noticed that almost all specs and notations in the manual say 'Different in different areas.'
Utterly stuck, pretty much terrified and daren't fit the lower rated caps....or dare I?
Any help and advice really appreciated.
 
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oldnotbold said:
Recently purchased a JVC S-55 integrated amp and discovered tone controls had no effect. Purchased 100uF /35V caps for tone control board (C217&218 and C221&222) as per JVC Service Manual spec. in 'HiFi Engine', only to find that all those actually fitted are 220uF/35V.
Then noticed that almost all specs and notations in the manual say 'Different in different areas.'
Utterly stuck, pretty much terrified and daren't fit the lower rated caps....or dare I?
Any help and advice really appreciated.
Click to expand...
The rated voltage is the parameter to be concerned about, and given they're the same voltage, there's nothing to worry about.

Differences in capacity in a tone control circuit may give different tone control characteristics than before, but given it currently doesn't work at all (are you sure this is due to bad electrolytic capacitors?) it's not likely to be a problem.
 
oldnotbold said:
Many thanks for that...and no, I am not at all sure about the caps, but as a rank amateur it is all that I could think of!
Click to expand...
If the unit is otherwise working correctly, it's unlikely the capacitors have failed in the tone control circuit and nothing else. Possible, but unlikely.

More likely is that either the tone control is switched off or bypassed -- look for something like a "tone defeat" or "direct mode" or similar button/switch -- or the relevant controls/switches are dirty (clean them with Deoxit or other electrical contact cleaner) or an electrical connector has been disconnected.
 
Really grateful for that - thank you. I do have a can of DeOxit so I will do as you suggest, check for any pushed-in buttons and also for any loose connections.
The physical design of the machine's internals is so tight that it doesn't make for easy access, and if someone has been in before, a loose connection could be a very likely scenario.
In any event, now that I am inside and have the new caps, I think that I will fit them anyway. Although the tops of the existing seem secure, the base of all of them is surrounded by some sort of dirty looking excess, not something that I can see in other areas.
 
oldnotbold said:
Although the tops of the existing seem secure, the base of all of them is surrounded by some sort of dirty looking excess, not something that I can see in other areas.
Click to expand...
That could certainly be leaked electrolyte from electrolytic capacitors, though it might be assembly glue used to hold capacitors in place during manufacture. If it is leaked electrolyte, try to remove it thoroughly as it's corrosive and will eat through PC board traces and component leads.
 
Yes, just about to do that now. It is dark brown, quite hard and solid and I would have thought that glue would have some sort of 'give' in it still.
My first attempt will be with Ambersil PCB cleaner, but my guess is that a water based solution to soften it might be a better bet.
And just to reiterate, I really do thank you for your interest and your answers.
 
Sorry to be a pest, but I now think it is glue - something that I never knew was part of any PCB process.
I have examined the base of all the removed caps and I can clearly see (and feel) residual glue around the underside of the base, with no evidence of any electrolyte leakage that I can see around the base or from the pins.
Bearing in mind your comments, I will remove what I safely can, but leave the hard to reach areas knowing now that it will not damage to the board.
 
oldnotbold said:
Sorry to be a pest, but I now think it is glue - something that I never knew was part of any PCB process.
I have examined the base of all the removed caps and I can clearly see (and feel) residual glue around the underside of the base, with no evidence of any electrolyte leakage that I can see around the base or from the pins.
Bearing in mind your comments, I will remove what I safely can, but leave the hard to reach areas knowing now that it will not damage to the board.
Click to expand...
Some glues become corrosive or conductive over time. It's possible if the glue became corrosive that the caps, or other components in the glue, are no longer connected, as the leads have been dissolved. If it has become conductive the components could be getting bypassed through the glue.
 
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