Marshall MG 15 cdr sound gone bad.

[donpalabras]

I got a new Marshall MG 15-CDR a while back and really liked it as a practice amp, until the sound very suddenly became lousy...breaking up and with almost no sustain. Anybody know what happened? Considering the low price of the amp if it's not an easy fix I can perform myself, I'd just as soon get a new one as pay for repair.

[Enzo]

How old is it? they come with a warranty.

Does it sound the same in the headphones? Does plugging something in and out of the phones jack a couple times "wake it up?"

Ball up your fist and whack the top of the amp. If that has any effect, there is a loose connection somewhere.

On my bench, I would isolate the problem to the preamp or power amp or the speaker. I'd suspect that TDA2050 power amp IC. I'd check the speaker return resistor R34. I'd make sure hte power supplies were OK, +/-about 20-25v for the power amp, and +/-15v for the small ICs.

[donpalabras]

Thanks for the reply. It's fine through the headphones, but no amount of violence or cajoling has any affect on the sound without phones. I'll try checking that return resistor next.

[52 Bill]

It's fine through the headphones...

I believe that the headphones are driven by the power amp, so if the sound is fine through the phones, then the amp either has a bad speaker or the headphone switching jack needs cleaning.

With the amp off, try squirting a little contact cleaner into the headphone jack and then plug and unplug the headphones in and out of the jack a few times to exercize the switch contacts, then try the amp. If that doesn't help, try a different speaker.

[Enzo]

What Bill said, exactly.