Marshall AVT 50 burning r58

[Hipnote891]

Hi,

Newbie in an old body :-). Working on a AVT 50 h. Initial inspection showed burned R 58. Looking for schematic on here still. I am sure this has to be common?
Any help ?

Thanks so much I need it!!!

[g1]

R58 burns if there is excess feedback or oscillation at the speaker output.
See this thread for schematics: http://music-electronics-forum.com/t13445/

[Hipnote891]

Marshall AVT 50 burning r58

R58 burns if there is excess feedback or oscillation at the speaker output.
See this thread for schematics: http://music-electronics-forum.com/t13445/

Thanks so much ! It's fixed and making music again! I can not believe my authorized service center had this for 9 months with hands raised saying " I don't know".

Thanks you, thank you Thank you.
I have learned so much in this process I am now hooked:-)

Hipnote

[g1]

These days it seems "authorized" often means they have authorized payment for whatever parts they order from the manufacturer and that's about it .

[Enzo]

Let's get the whole story. I can't imagine even a crappy service place not noting a burnt resistor. Resistors do not burn themselves up, so have we cured whatever burnt it up in the first place? Or are we just waiting for it to go unstable again and burn up another. Maybe THAT is what the service center couldn't cure.


Some OEMs like Fender have you take an exam to be a tech for them. In fact Fender even has three levels of tech, bronze, silver, and gold, and also breaks that down into electronics, acoustic instruments, electric instruments. But most have a basic app. And what most of them are looking for is an existing business operating from a commercial space. IE not some kid in a basement. They also expect a basic credit rating.

ANyone who does service knows that MOST repairs are not taxing. And a tech with rudimentary skills can replace the broken jacks and controls or fix a broken wire or solder joint. And that satisfies the majority of need for a field service network.

Although I admit that does not make a very inspiring wall plaque.

[g1]

Have you heard the one about the tech who Fender "certified for life"?

[Hipnote891]

Marshall AVT 50 Burned r 58

Have you heard the one about the tech who Fender "certified for life"?

Hi,
Thought I would clear up the story about the service center.
First this area of repair is not my expertise. As a much younger man I worked for a company developing a midi guitar preamps and effects I have no formal electronics training. I learned on the job from guys that were patient and excited to teach " the Rookie". Luckily what I lacked in experience I made up for with creativity and determination. I have repaired many pieces of gear over the years, but I am no expert. I am a safety first, understand how it works, and study the schematic before I attempt anything. I would love to have the skills you guys have in troubleshooting!!
About the story,
1. They noted the burned r58
2. I asked what they tested, output?
3. They said that was not part of the troubleshooting
4.they said they replaced r58 and it burned again ,but they did not know why?
5. They threw there hands up
6. Charged me 125 bucks for ?

I took it upon myself to fix it. So I studied and searched and I found this forum. I know that resistors don't usually fail on there own. So I checked outputs. Sure enough, Voltage!
Having studied the schematic I knew about the output IC.
So, I replaced R 58. C92, and the tda7293.
It's seems fine now. Although I feel this might be an inherent problem. Since I have been sent about twenty links now.
I can not thank you guys enough for the help. I love fixing stuff. Next is an ampeg tube head. I may ask for help if its okay?
Peace,

Hipnote

[Jazz P Bass]

As a rule, anytime I get an amp where the resistor (R58 in this case) of the 'zobel network' is blown, I will also replace the associated capacitor. (C92).