Marshall AVT 150 Valvestate

[Tubehead]

I've replaced IC 8,9,and 10 trying to eliminate the problem. Only the accoustic channel works. Without a schematic, I'm just guessing. Could you send a schematic for AVT 150? My email: lundyevo@yahoo.com
Any help would be greatly appreciated.

[amptech]

marshall avt 150 valve state

Hi there,

You say you have changed some ic's on the preamp board and the fault is still there, did you use the correct replacements for the old ic's 5201a?.
Ic 2120d is recommened by marshall to replace that and check replace tl071 at the tone stack aswell, did you replace the predrive valve 12ax7 use ecc83 in it's place and check resistors around that part of the circuit plus the cap's 33uf 450v/10uf 350v. sometimes when there's weak or no overdrive channel replace the old valve and see if things improve.


Amptech

[Tubehead]

Avt 150

I think my model is a later rev. AVT 150X. All the op amp chips are NJM072BL's which I replaced with NJM072BD's. This rev. also Does not have TDA 7293's for output. Looks like Marshall upgraded to SAP 16 NY 3117 and PY 2N28, which work fine. 12AX7 is good. Using a probe, the signal will go through the amp from ground points (like the pot chassis) and the legs of some of the channel switches, which makes us think there is a shorted cap maybe. All of the work has been done on the front pcb(the one with all the knobs). We haven't done any work to the preamp board, just made sure the 12AX7 is good. My tech thinks the problem might also be with the switching. However, the leds on the switches lit up and turn off when pressed. Also, the acc. channel works when pressed. Another curious thing is a gtr signal in the effects return will go thruogh the clean channel. THese schematics will help a great deal. You guys are a godsend! Again, any help is greatly appreciated.

[Enzo]

OK, so you don't have an AVT150 then. The AVT150x is a different model, no matter they are both similar. SO the schematic set is different.

What exactly are we trying to fix? Welcome to the place, by the way. I might suggest to all involved that it is always better to start a new thread for your amp than to tack it on to the end of another amp's thread. This AVT150x is now the fourth AVT in this 18 post thread. The first amp had no output at all, now this one apparently has output on some channels but not others. Well that isn't the same problem, and it is a different amp model.

SO what exactly are we fixing? Loss of some preamp channels only?

LEDs working has no bearing on whether the switching ICs are working.


If the two OD channels don't work, then look at IC1 at the input. You already rplaced IC8. The DG212 at IC2 could be bad.

If the clean channel also works, then this is the point they join together.

If yuo still don't have the schematic, I have it.

[Tubehead]

Avt 150

Thanks for the reply. I have the schematic thanks to Amptech. You're awesome! This is what I'm fixing: The acc. channel is the only one that works. OD1, OD2, and Clean do not. The Clean channel will work if I plug into the efx rtn in back. That tells me something, I don't know what.THe 12AX7 is good. We're going to replace IC1 next. We have 1 072 chip left. The others we replaced before we had the schematic, hoping we'd get lucky. Come to think of it, our schematic is different. You're right. Could you send me one please? lundyevo@yahoo.com. You guys are so much help I don't know how to thank you.

[Tubehead]

I screwed up in my last post. The schematic I have is wrong. AVT 150H not X. Could you send me the 150X if you have it? THanks: lundyevo@yahoo.com

[moulos]

Mate i needs the AVT-150 Valvestate 2000 schematics

Can you send them pls?
My email is : ioan_balab@yahoo.gr

Cheers

[mrgreengenes84]

AVT150 schematics

Someone can send me the AVT150 schematics.I've your same problem...I've burn a lot of TDA7293,help me please!

Thanks!

[mrgreengenes84]

Output Ic's blown

I've the same problem,I've burn a lot of TDA & can't fix it!
Quazcha have you solved?

[quazcha]

please read previous posts

The TDA7293 is used in AVT150 and MG100HDFX. Check out post #13 under this topic I had an open PC trace...I will send schems

[Enzo]

If either one of the TDA chips is blown, replace them both. Also make sure the 0.22 ohm 10w R111 is not open.

[mrgreengenes84]

Thank you Quacha,today I'll try to fix this amp!!!

[mrgreengenes84]

Fix AVT150 Power Amp

Someone have fixed AVT150 Power Amp?I need some advice.It's necessary to replace ONLY TDA's (both) to run this amp?Or some replacement?

[thedetoure]

hi just wondering if you have a schematic for a avt150 thanks. thedetoure@hotmail.com

[cencio]

Mate i needs the AVT-150 Valvestate 2000 schematics

Can you send them pls?
My email is : kempe@inwind.it

Luciano