Beta Lead humming / buzzing

[Dr. Gonzo]

Hi guys and cheers from Berlin!

My son (13, very into Doom with his SG clone) bought his first amp himself, a broken Beta 410 combo, and now I'm the one who has to take care of fixing it.

Serial number is above A-52175 so according to the service manual it has already the newer slightly changed layout.

When switched on it makes a humming / buzzing noise no matter what position the knobs are in. I recorded a short video, see Google Photos link below.
https://photos.app.goo.gl/sgx3Wq9sRsDbVpow6

I tried the line out (master and preamp) with another amp but the noise remains just the same. Only difference is (logically) that now the volume can be controlled on the other amp.

According to this post it could also be a broken OpAmp. Any other suggestions?
https://music-electronics-forum.com/forum/amplification/guitar-amps/maintenance-troubleshooting-repair/5963-sunn-beta-lead-restoration#post134912

I have a friend who is very much into repairing and building amps but he has no experience with this model. Should he just measure through all the components and replace the broken ones?

Thanks for your help and have a nice weekend!

[EdBass]

I think so.

I don't have much experience with the Sunn transistor gear; however, I did buy a broken 4X10 Beta Lead several years ago from Guitar Center for $25. Took it to my tech and he fixed it quick, he commented that it was pretty simple early transistor technology (I think he mentioned "second phase of SS guitar amps"), but my takeaway was that it was easy peasy,
I'll bet your tech can get it back up easily.

Good Luck!

[loudthud]

If you look at the thread you linked on Music Electronics Forum, the first amps fixed had blown output transistors.

If your friend is self taught and can only fix tube amps, don't give the amp to him. Find someone who has been to technical school and has experience fixing solid state equipment. It is unlikely that the amp can be fixed by someone just replacing components without the technical expertise to determine what part of the amp is malfunctioning.

[Dr. Gonzo]

Thanks guys! So I'll try to find a pro who has experience with solid state amps. The amp was pretty cheap (20? including footswitch), so we can invest some money in the repair and still got a good deal.

Have a good one!