valley dynamite problems

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Rob Flinn said:
The problem is definitely around U4 pin 7 from my V measurements.  Also U4 is getting very hot so it must be dumping some current somewhere.  I can't see any shorts & have reflowed the soldering in that region

Checking the bad channel against the good one some of the resistor readings are low, but if I measure the resistors lifted then they measure ok ........................ Hmmmm  :-\

U4 pin 7 also connects to the led array and the control jack.......maybe disconnect the LM339 array ?
 
I know in circuit readings can be inaccurate, I was only lifting the ones that were very different to the same ones on the working channel.

Quiescent the U4 > Vca is at -10.5v  on the good channel -1.5v.  The Av is 2 and the input around 3.5v ??

I think this problem mainfests itself in the op amp before that. which has 15v on output as opposed to 0v on the good channel.  This would concur with that fact that the GR mter is pegged & it is fed from this point.

Interestingly the meter still pegs if I remove U4 & U6 ???? I guess this means the weirdness could be coming from the meter circuit.
 
Yes it's something to do with the meter circuit.  If I remove the 0ohm link that feeds it U4 is cool and at normal voltages.
The GR meter stops pegging but just the -20dB led remains lit !

Now where did I put those spare LM339's ??
 
OK problem was a short between + volts after the 2watt 2k resistor & the meter feed.

You can check whether this is your problem by lifting 1 end of J14 (I think it's J14, sorry should have checked before I put it all back together). 

Thanks for everyones help with this !
 
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