Mesa 50/50 isssues

Hey guys, theres a local guy that's wanting to trade me a few things for this Mesa 50/50. You can see on the board that it's got a few resistors burned out. I don't know the extent of the damage. He told me that someone tripped over some cables while he was gone and it broke the solder joint, then he turned it on, saw a spark then turned it off. Does this look like something that can be fixed reaonably cheap? He doesn't want to send it to mesa, but i figured anyone with a schematic could figure it out. It's next to the preamp tube, not power.

Looks like it has two blown heater resistors. The yellow wire going from the output jack to the preamp tube board is a bit toasted too. Not sure what would have caused that. I know that if you run one side without a load it could harm things but as far as i know, he was running it in stereo. Looks like a pretty simple fix.

Wow, I'm no expert,but I bet there was a small fire in there for a minute.
That's a real crap shoot. PCB could be F'd. That multi pin connector looks dicey too.
Personally, I wouldn't pay more for something like this than what I thought it was worth as spare parts, so not very much.
Even if it is totally fixable, you're going to be pulling the pcb to do the work.
What's your time worth?

Edit: just saw your last post - why would there be resistors in the heater circuit? just wondering...

fusedbrain":2905e1x9 said:

Wow, I'm no expert,but I bet there was a small fire in there for a minute.
That's a real crap shoot. PCB could be F'd. That multi pin connector looks dicey too.
Personally, I wouldn't pay more for something like this than what I thought it was worth as spare parts, so not very much.
Even if it is totally fixable, you're going to be pulling the pcb to do the work.
What's your time worth?

Edit: just saw your last post - why would there be resistors in the heater circuit? just wondering...

Click to expand...

I just happened to see that exact scenario on the Boogie Board. Im basically trading this guy a couple hundred $ of studio monitors for this. This almost sounds like a short in the power tube that caused that. he said the speaker cable was broken somehow and as soon as he took it off standby, POOF. From what i understand, those resistors regulate HUM and aren't vital the the working of the amp. I would still replace the burnt yellow wire too. It really doesn't look like too big of a job. replace the resistors, wire and clean up oxidation.

But, that's why im asking here, for better opinions.

Looks like the scheme can be found here: https://schematicheaven.net/m-mesaboogie.html
So actually there could be 2 x 100 ohm elevation resistors in the heater circuit, but given the proximity to the 2 x 47uf / 100v caps, I think those may be R241 & R242 in the bias supply.

Edit: yeah I think I can see brown / black / brown bands on the least burnt resistor, so they look like the hum balance or elevation resistors.

I'm just not sure how much of a pain in the ass this would be to repair if the traces are melted on the board. Just about anything is fixable I guess, but just remember to factor in your time, and a new set of tubes.

Good luck with it if you decide to do a deal for it

Ive got spare tubes. Nothing but time, and a little cleanup. Ive seen them go for $500 or more. Im getting it for less than half that.

Looks like arcing in the tube socket causing heat and fire nearby (carbon trace coming from the tube socket). Two hours of work plus parts (reasonably, the tube socket should be changed because it will arc again at some point). It's a $200 job minimum.

Owner said it made a hell of a spark, but the tube socket is fine. I still did turn it down after asking a somewhat local tech what he thought