Marshall AVT 150 Valvestate

[Drinkofmars]

My AVT 150 is working normally apart from the lack of the 2 overdrive channels, i can still heard a vage sound but thats when the channel and master volume are cranked right up any ideas as to what could be the problem??

[Enzo]

Look for a bad op amp IC in the OD channel circuit. My memory is foggy, but I seem to recall IC8 being the usual bad one. Look at each IC and see if any has DC on the output pin. DC on output is usually a sign of a bad chip.

[MARSHALL BUSTER]

Marshall AVT 150 Valvestate

Hi guys n gals
I have the same problems as listed allover this page, seems to be a trend on these amps, I would appreciate a copy of the schematic if someone could send them to me please. Do i have to post my email address or can you get it some way??? im new!!!
Thanks.
Mark

[amputee]

Can I also suggest when fitting a new set of tda boards , short out the 22 k's ( 1 watt) to totally ground the supply rail . Any dc will send you off for two new boards . I was having a chat with the cheif tech at Marshall (great guy I might add) .He suggested this as the rail stays hot without a load and you would need to put all the connections on at the same time ..If your name is Kali ignore this post...

Dps

[Disco Dave]

Valvestate avt 150

Just to update as I postted the original. I got hold of 2 TDA replacement ICs but damaged the boards removing the original ones . Have recently ordered new PCB s with tdas mounted. Hope it will work with these in.Awaiting delivery and if anyone has the schematic then please send. can supply email address.

[Disco Dave]

Have replaced the output boards with tda chips but unfortunately the problem persists. Any ideas appreciated. I have a multimeter.Also if anyone has the schematic please send to ddjbarker@Hotmail.Com.

[Disco Dave]

Could it be the valve as there is no glow when power is on.

[amptech]

avt 150 amps.

It must be a month of these!

had a whole heap of these of late with many different faults from total dead!
blow main fuse to dead front preamp stage's....

Had the pcb o/p stage solder tracks brunt away so end up moding the o/p stage via fitting a different and better power block made up from mosfet's and beefing up the 1000uf caps to 4700uf doe's the trick!
The ht supply to the 'o/p' ic is +- 47 volts so you can mod fit a block that will handle that plus give you near to rms power. mine gave 140w rms and still being hammer daliy

Even the mains tranformer was napped clean from the chassis!

The .22 ohm resistors at the preamps primary ac feed in was o/c so a quick replacement sorted that out and next broken pot's due to heavy drop abuse.

I nearly always see these units with the same old fault's burnt o/p stage so beefer o/p stage fit and your ready to jam

[Jimmy74]

I'd be needing the schematic for the AVT150 too, please send to:

jimmy74@hotmail.it

thanks

[Jazz P Bass]

Tech help

You might want to consider taking it to a reputable tech.
Just a thought.

[tkdrew]

looking for a schematic for the AVT 150H

As the title says, I'm trying to find a schematic for an AVT 150H. Any help is greatly appreciated. tkdrew2002@yahoo.com

[Slib]

AVT 150 tda 7293 seem fine, fuse still blows though as I power on.

Hello
I have tried to find the problem but I cant seem to locate it. My tda 7293 seem fine, but the fuse nnext to the power input keeps blowing anyway. I insert a guitar cable and plug the preamp into the internal input to the amp, and when i power on there is just a flash right where the fuse is located and the amp shuts down. I have checked the tdas, but as I said they seem fine. I dont know what else could be the problem. the little tube thing doesnt have any orange glow or anything, and the only place where i can smell anything getting fried is the fuse.
Any help is much appreciated
Thanks
and my email is nikolaidislash@hotmail.com if anyone has any solution.

[Enzo]

You mention twice you checked the TDA7293, but HOW did you do that? Did you check with an ohm meter to se if either power supply in is shorted to ground or shorted to the output pin? Are teh p[ower supply pins shorted to each other?

There are two TDA7293 are there not? Unplug the wires from BOTH, put in a good fuse, and power up the amp. Does it still blow a fuse? If the fuse remains OK with the TDA7293 modules unplugged, then they are bad.

[saranden]

Marshall AVT150H and AVT275

I have repaired a few of these now, and I have found it easier to cut out the TDA's by bending the component back and forth about a dozen times, then remove the pins with a hot iron on the pin only, then blow the hole rather than burning the traces of with too much heat. I mount an IC socket onto the TDA board, one strip on each line of holes, then once I have mounted the module back on the heat sink, I use hot glue under the PCB to stop the PCB from being shocked off of the TDA. No damage to the board and an easily replaceable TDA in the future. REMEMBER to discharge the preamp before you connect the TDA'a back to the preamp or it will blow them again as soon as you power up (most of the time)....i use a bulb across the pins, then measure the voltage from them to make sure they are almost zero.

[Zero Kool]

I too need the AVT 150 schematic any help appreciated. Thanks!
doctord@vespertechnologies.com