Marshall AVT

[elipsey]

Interesting. The AVT150h I repaired claims 150W RMS into 4 Ohms from 2 TDA7293, perhaps 75W is still too too much.

For what it's worth the guy said it popped when he touch the speaker cable tip to the chassis while idle. I have no idea if this is a bad thing to do, evidence of a design defect, or merely the insult following some greater injury (or a combination of these).

[Valvehead]

thanks for all the info guys. I ordered 2 new boards . I couldnt save 1 . These boards had the chip replaced before, and arent too pretty.....i will drain caps in the amp before installing. I found the spacers/washers......will add some fresh grease and power it up with my current limiter .

[g1]

For what it's worth the guy said it popped when he touch the speaker cable tip to the chassis while idle. I have no idea if this is a bad thing to do, evidence of a design defect, or merely the insult following some greater injury (or a combination of these).

The sleeve (neg.) of the speaker cable is usually connected to chassis. So if he touched the chassis with the tip, he placed a dead short across the output. Tube amps don't mind this, but for solid-state amps it is usually fatal. Even in solid state amps with short circuit protection, it may not act fast enough.

[Valvehead]

Ok guys, i got the new boards. Problem.........

the AVT275 pcb is wider and deeper--i can dremel the back of the pcb easily so the chip is flush for mounting to the heat sink.

the other thing is, the new 275 pcb has about 6 extra parts on it on the right end--you can see them in the pic.

my avt50 boards do not have these parts . The place i bought these from can offer no tech advice and said to call Marshall---but i cant find a number for them.

anyone know anything on this subject?? I sure am not going to just plug these suckers in !

new boards =

Marshall AVT Power Board Kit AVT275X | eBay

[Valvehead]

heres the new pcb , on left , avt50 on right

[52 Bill]

What is the additional circuitry connected to? It may be there to protect the chip from static discharges.

[Valvehead]

2 resistors
2 diodes
2 10uf caps

[Mick Bailey]

It;s worthwhile reading this thread and the advice on powering up/monitoring, even though it's for a Mode Four. It's saved me from disaster a few times;

http://music-electronics-forum.com/t3873/

Also, check the cap polarity - I've had a couple of boards with flipped polarity.

[52 Bill]

2 resistors
2 diodes
2 10uf caps

Okay, what are these parts connected to?

Maybe you can post a clear close-up photo of the top and bottom sides of the pc board and we can figure it out for ourselves.

[Valvehead]

I finally got a Marshall guy on the phone. He said the new boards are compatible and have been modified .