Marshall AVT150 OD1 & OD2 are half the volume of the clean and AC Sim Channels

[quazcha]

Hello all, This is my first post.
I bought a "basketcase AVT150" from feepay, I replaced two pairs of TDA7293's before noticing an open pc trace from pin 1 of connector C230 & pin 1 of connector C18*(9or5?) (the power amp A and B connectors.) a HEARTFELT MANY THANKS TO ENZO FOR THE SCHEMATIC!!!! The BDOP (Brilliant Displays Of Pyrotechnics) have stopped and I have sound! However with all knobs at "5" I have a considerable volume difference between the channels as I toggle thru the 4 modes. The AC Simulator and Clean channels are equal at a "heard" volume level of about 100%, while the OD1 and OD2 are "heard" at about 40-50%. If I turn OD1 and OD2 volume and Gains to 10 It still does not seem to be as loud as the AC Sim and clean channels on 5. There is a difference when I increase gain/volume for each OD channel so they are not "dead" I have tried two different known good 12ax7's. Help? any ideas?

[Enzo]

This is probably not related to the blown output ICs.

I think you will find a bad op amp on the preamp board - I forget which one it is. it is not usually the one closest to the input, it is usually one firther towards th center of the board. Nonetheless, check for DC offset on the output pins of the op amps on the preamp board. If one shows several volts, try a replacement. If my memory is working, those are one sided op amps - SIP packages - all the legs on one side.

[djw]

I think you will find a bad op amp on the preamp board - I forget which one it is.

Hi Enzo,

I remember a thread here in 06 about the op amp issue.
Are schematics and the tech bulletin, still available though you?

My 150 has the hiss.

[Enzo]

Yes.

[djw]

Thank you sir,

Email on the way.

[quazcha]

OD 1 &2 Hiss or volume problems

Replace IC#8 tlo72 sip from www.mouser.com it is in the center of the front pcb