RF T1500-1bd

[ultra]

Got this amp in for repair and it draws excessive current.
After removing the x-over card and replacing all TL072s it idles fine but
I can only trace input signal getting into the x card. Nothing comes out.

 

[Perry Babin]

Are you sure that the problem isn't the switch or a pot?

Are you sure that you have supply voltage on all op-amps?

Which op-amps have audio on their outputs on the crossover board?

 

[ultra]

yes, i worked the switch
all opamps have +/-13V
none of the opamps has signal.
I even removed the x over board and powered it from an external supply, injecting signal in R56.
I can see it smaller on the other side of the resistor, and then i loose it

 

[Perry Babin]

When you connected the board to an external supply, did you also provide a ground for the board from the split supply?

R56 feeds the inverting input of the op-amp. You should not see any signal on the op-amp side of the resistor when the board is working correctly.

 

[ultra]

I grounded the inner first pin of the second header (J200) of X-over card.
I can only have sine at pin 1 of U100.
There is sine at pin 1 of U101 but on top of the minus DC rail.
As things are right now, the amp pulses 12-13VDC on the output.

 

[Perry Babin]

You may have a defective xover pot. Try bridging all 3 pins for each section of the pot to see if the audio will pass through the op-amps.