HT Club 40 Volume Issue

[Teleblaster]

I'm buying one used at a really nice price, but with an issue as well.

From the seller:
"Low volume issue and needs tlc.
I tested both transformers with a test that's 95% effective and they both tested out good
(you'd want to stay away from an amp with blown transformers)

i replaced 4/5 burned out resistors on the main board, the bias adjustment pot also just kept spinning and spinning (it's only supposed to spin from like a 0-10 scale, instead of spinning infinitely) so i replaced the bias pot thinking that might be the issue

once i did all this the amp finally started working again and producing sound but it's a very low volume, not loud enough to keep up with drums at all

main thing keeping me from finishing the repair is that blackstar is a stingy company and keeps their schematics top secret. you have to take it to a "certified korg dealership" because korg is the only reseller that deals with blackstar anymore. if i had access to the schematics i could further diagnose it. besides that i fixed everything i could"

Anybody have any insight as to what could be the cause of the low volume? I'll fix it myself if I can.

[8len8]

I'd stay away from the amp. There's no knowing how much it would cost to get it running again. If you can't afford to buy one in working condition then I'd wait and save up more money or look into a cheaper model.

[thephantum]

Someone obviously either abused the amp, or tried to "fix it" with little understanding of electronics, or tried to unsuccessfully mod it, or all of the above.

So unless you get lucky and something is power starving the output stage, it's most likely going take an oscilloscope and signal generator to figure out what's going on....and there's probably multiple things going on. So, unless, you have that kind of diagnostic equipment AND can get the amp dirt cheap ($50 or less), stay away from it.

[Teleblaster]

Thanks for the insight; he's selling it for $100.
His friend is a tech, and that quote was his answer to my question "What IS the low volume issue?"
I guess he took it to his tech friend to try to fix it and didn't have much luck.
He recommended I take it to a Blackstar dealer to have it looked at.

[thephantum]

Again, unless you are going to fix it yourself, stay away from it. "4/5 burned out resistors" as well as the bias pot have already been replaced and the amp is still not working correctly. It's a total crap shoot as to how much more is wrong and how much it's going to cost to repair it.

As an aside - Whenever I hear a tech say, " I can't diagnose it without a schematic"...that's a red flag and tells me to stay away from that tech. It's pretty easy to trace out a circuit by just looking at a PCB. The problem is there a lot of people calling themselves "techs" that do not understand circuit design or even how a given circuit works. All they can do is test for bad resistors, capacitors, etc. It's better to find a tech that understands how circuits work and uses test equipment to diagnose those circuits. There's too many just blindly testing components and hoping for the best.