Marshall 9001 missing -15v for OP amps

[Rotorcraft230]

Hello everyone and happy new year.

I have a 9001 tube preamp and need some help troubleshooting it. It's missing the -15vdc for the op-amps.

here is what I have done.

replaced 79L15 (RG1) still no -15vdc out

lifted the output leg and soldered the ground and input back in and the -15vdc was there.

I have +15vdc at D11 and -.009vdc at D12 measured after the lifted leg was resoldered in.

BR1 measures 19.5vac and 19.5vac 23.8vdc and 22.8vdc.

sounds like to me there is a component shorted and sending it to ground.

need some help on where to go from here.

thanks

 

[tschrama]

Replace the opamps one by one… ?bit of work if they arent socketed.

Does any of the opamps or resistors get warm?

Maybe replace the 7905 with a 1k ? Just to see what kind if current is flowing? Can you measure any current theough the 7905?

 

[Rotorcraft230]

Forgot add schematics

 

[Jon Snell]

It could be either C46 or C35 short circuit but it may also be a faulty op amp.
I would lift pin4 of IC4 then IC5 first as they do not have the 10 Ohm feed resistors on the -ve supply. If it was either IC1, 2 or 3, I would expect more than 0.5volts on the -ve rail and zero on pin 4 of the faulty chip, due to the 10 Ohm resistors in series with each pin 4 of the op amps.

 

[Rotorcraft230]

It could be either C46 or C35 short circuit but it may also be a faulty op amp.
I would lift pin4 of IC4 then IC5 first as they do not have the 10 Ohm feed resistors on the -ve supply. If it was either IC1, 2 or 3, I would expect more than 0.5volts on the -ve rail and zero on pin 4 of the faulty chip, due to the 10 Ohm resistors in series with each pin 4 of the op amps.

Hi Jon, thanks for responding.
I lifted one leg on c46 and it measured its value, I didn’t check c35, but I do have a “Blue ESR tester “ and it measured good, I can remove it and check it though.

Hiw do you lift one leg on a IC that has 8 legs?

 

[Rotorcraft230]

It could be either C46 or C35 short circuit but it may also be a faulty op amp.
I would lift pin4 of IC4 then IC5 first as they do not have the 10 Ohm feed resistors on the -ve supply. If it was either IC1, 2 or 3, I would expect more than 0.5volts on the -ve rail and zero on pin 4 of the faulty chip, due to the 10 Ohm resistors in series with each pin 4 of the op amps.

Hi Jon, you led me to C35 and that was it, shorted, replaced the cap and it works,

Thanks for chiming in

Cheers