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yamaha c70 preamp phono dead kink of

D

darrelb

AK Subscriber
Subscriber
my next c70 preamp mostly a dead phono section the left side sounds decent the right is dead but the disc direct works well.
I recapped the preamp and the line inputs sound great, i've looked for iffy solder joints and reversed caps
and found nothing obvious. only the right side of phono 1 and phono 2 does not work. tapping the
pc board changes nothing.
 
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Dis-assemble SW101 & SW102 and clean..
 
Last edited:
i have taken sw101 and sw 102 apart and cleaned the there was some tarnish there now that is gone.
disc direct on mm works, disc direct mc weak and distorted.
phono 1 left works right is dead
phono 2 left works right is dead
mm 100 ohm is in mono
mm 47k right is dead but left is ok,i checked all the soldered pins on sw101 and sw102
and all were good also the tr 537 and tr538 get hot after a couple of minutes of operation
 
i replaced ry 101,ry 102 and ry104 and nothing has changed still dead right channel just as before
 
avionic just to back track a bit the first c70 i recaped i used all nichicon e caps nothing else
was changed.
the last two c70's i've woked on had problems with the phono sections on the last two preamps
i replaced caps 10uf and under with the same size wima film caps is it possible that the phono
sections don't tolerate the nonpolor caps?
 
darrelb said:
avionic just to back track a bit the first c70 i recaped i used all nichicon e caps nothing else
was changed.
the last two c70's i've woked on had problems with the phono sections on the last two preamps
i replaced caps 10uf and under with the same size wima film caps is it possible that the phono
sections don't tolerate the nonpolor caps?
Click to expand...
It should be fine..
 
back to the fight again ,i tapped on sw4 several times and reflowed the pins and even followed
the traces and reflowed those pads and nothing changed.
again the mm and mc disc direct works but the right channel on phono is extremely low
i'm begining to think about changing sw4 and see what if any thing changes.
 
Bummer...
avionic said:
Do you have an audio signal generator and an O'scope ?
Click to expand...
Need to figure out where the signal is getting lost. We are kinda down to possible cracked circuit board trace or solder pad.
 
Check your relay coil voltage on RY101.. Approx. 24vdc..
 
i checked the voltage on ry101 and i get next to 0 volts,i looked at the pc board and it was not
cracked then i took my big eye and looked closely at the traces around the phono section
and did find one trace that was suspect.
 
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