wondering if anyone is familiar with this particular amp.
the issue appears to be thermal runaway and bias stability.
one channel's heatsink gets twice as hot as the other.
thus far bias adjustments are not providing positive results and all measurements are as per service documentation spec's.
if it comes down to replacing components a good many are obsolete and my searches thus far are bearing no fruit (i.e. not a snowball's chance in h*ll)
short of finding a donor chassis with good components i'm thinking it might be a lost cause.
as i am still trying to gain a better understanding of jvc's "super A" design i hope someone can help!
the issue appears to be thermal runaway and bias stability.
one channel's heatsink gets twice as hot as the other.
thus far bias adjustments are not providing positive results and all measurements are as per service documentation spec's.
if it comes down to replacing components a good many are obsolete and my searches thus far are bearing no fruit (i.e. not a snowball's chance in h*ll)
short of finding a donor chassis with good components i'm thinking it might be a lost cause.
as i am still trying to gain a better understanding of jvc's "super A" design i hope someone can help!
Hi!
this amp is absolutely White Raven,
excellent,
do not spoil it by making it the chassis donor,
start to measure semiconductors with DVM and pcb traces for cold solders.
this amp is absolutely White Raven,
excellent,
do not spoil it by making it the chassis donor,
start to measure semiconductors with DVM and pcb traces for cold solders.
ok you like this model and i'm not going to frankenstein it in any way!
do you have anymore info as to what could be wrong?
thus far thorough inspection and testing has not provided anything that would resolve the issues of thermal stability and bias drift.
i'm hoping that i'm dealing with a known issue and not a unit that because of age would require a complete rebuild as it appears many of the transistors are obsolete and "unobtainium".
it is functional but i am concerned that it will head south if i can't fix it's issues
do you have anymore info as to what could be wrong?
thus far thorough inspection and testing has not provided anything that would resolve the issues of thermal stability and bias drift.
i'm hoping that i'm dealing with a known issue and not a unit that because of age would require a complete rebuild as it appears many of the transistors are obsolete and "unobtainium".
it is functional but i am concerned that it will head south if i can't fix it's issues
adason
that's where i'm at.... recapping...but my previous experience with some of these "Super A" types from JVC are stories that require a bottle of scotch!!
it seems like doing anything that changes the operating point of any stage causes cascade problems!
in the past i've killed a few in attempting repairs.
your post came along while i was (slow) typing (if things appear confusing)
that's where i'm at.... recapping...but my previous experience with some of these "Super A" types from JVC are stories that require a bottle of scotch!!
it seems like doing anything that changes the operating point of any stage causes cascade problems!
in the past i've killed a few in attempting repairs.
your post came along while i was (slow) typing (if things appear confusing)
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I start with DeoxIT, cleaning all contacts...sometimes that takes care of some issues. You would not believe how many vintage amps with horrible distortion were cured just with DeoxIT.
Then, caps, as you are already doing...and maybe retouching some old solder spots, especially on parts with heat, as they expand and shrink, as they cool and heat with use...and then comparing good side with bad side. You are actually very lucky that way, when one channel behaves, one not. Its harder if both are affected.
Once you do all the above, post the schematics and show voltages for each channel in each transistor. I am sure there are clever people here to help.
Then, caps, as you are already doing...and maybe retouching some old solder spots, especially on parts with heat, as they expand and shrink, as they cool and heat with use...and then comparing good side with bad side. You are actually very lucky that way, when one channel behaves, one not. Its harder if both are affected.
Once you do all the above, post the schematics and show voltages for each channel in each transistor. I am sure there are clever people here to help.
that may have been the greater part of the issue dirty trimmer controls!
a cleaning and a re-tweaking/re-setting seems to have resolved things!
sometimes the simple things are over looked.....
still hope someone could provide more insight and wisdom as to the the what's, why's, and how's of the "super A" circuit....
a cleaning and a re-tweaking/re-setting seems to have resolved things!
sometimes the simple things are over looked.....
still hope someone could provide more insight and wisdom as to the the what's, why's, and how's of the "super A" circuit....
attached file
https://www.flickr.com/photos/trebor1966/21005652449/
and you can search "solid state" threads with keyword nonswitching to find more info
https://www.flickr.com/photos/trebor1966/21005652449/
and you can search "solid state" threads with keyword nonswitching to find more info
Attachments
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the regulator lives on another board so there's no chance that heat from a regulator is added.
it been good since cleaning the trimmer controls...
it been good since cleaning the trimmer controls...
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