Single Rectifier - Burnt Resistors in V1 Preamp Stage

[Engine09]

Burnt PCB sections have been grinded out with a dremmel and filled with overcoat, it does not look perfect but much better. Completely removed the 2 traces that came closest to the burnt section and bypassed with jumpers. Will post photos tonight.

Need to ask those with more experience, my plan is to reconnect the board and power it on without any of the tubes. Will check voltages at power supply first then each preamp tube and the power tubes last.

If all checks out I'll then install all tubes and check voltages again. Does that sound like the proper way to proceed?

[g1]

Well, I don't know how that happened as I have no time machine, but post #30 was a response to post #31.

[Engine09]

Be aware that the voltages will be higher with no tubes installed. So make sure the filter caps are not subjected to voltages above their rating.
A variac or lamp limiter is helpful for this.

Yes, without a load I wouldn;t have been suprised to see all voltages a bit higher than expected. But, I don't have a variac at home, don't even have access to one here at work.

I'm just trying to go about this with the proper procedure so I can catch anything funny before plugging in the brand new tubes and risking damage.

I could go through the spec sheets for every capacitor, but I know for a fact I can't even see the part numbers the way they're mounted and glued.

[Engine09]

Well, I don't know how that happened as I have no time machine, but post #30 was a response to post #31.

I posted under a different screen name by mistake, cleaned it up just so everyone can see it was the original poster.

[g1]

Well, you're only allowed 1 user name on the forum, so be sure to not do that again .
The cap voltages are shown on the schematic. The first stage filtering has two 300V caps in series, so good for 600V. I don't think you will go over that.
The second stage is a 30uf 500V cap, circuit voltage is shown as 450VDC there, so maybe have the meter connected to that node when you power it up. If it goes over 500VDC, shut down. A couple seconds at over rated voltage is not going to blow it up. The next filter stage on the other side of the 2K7 resistor is 450V caps, circuit voltage is shown as 425V, so check that node also. The rest should be fine.
Also, it's pretty rare for preamp tubes to have any gross faults that do damage, so usually firing up with just the power tubes removed is sufficient.
In this case, as the damage was at one of the preamp tube sockets, I would pull that one and the power tubes to do initial checks.

[olddawg]

Seriously... 5 minute epoxy (which this stuff might be with a little green dye) works fine, is readily available, and is much less expensive. Mix it and apply it with a toothpick. If you really want to match the color of the board.... Paint the repair with fingernail polish, lol.

[Engine09]

This amp sounds amazing, absolutely love it.

Finished the repair, checked continuity with the meter, cleaned the board, visually inspected everything then inspected again. Powered up without the tubes, checked all voltages, installed preamp tubes, check voltages again. All good. Installed power tubes, let it warm up and it was just crystal clear as soon as I rolled up the volume.

Thanks to everyone who took the time to help me out, I appreciate it. Was not familiar with the Mesa schematics and just needed to be 100% sure on those burnt resistor values. Will post photos of the repair tomorrow and a little synopsis to help out anyone else who searches out this thread in the future.

My other amp is a Marshall JCM 2000 w/ a 4x12 which I love but I am really enjoying having the Mesa option with the oversized 4x12, even at 50W this thing is incredibly loud.

Thanks again guys!

[Engine09]

Seriously... 5 minute epoxy (which this stuff might be with a little green dye) works fine, is readily available, and is much less expensive. Mix it and apply it with a toothpick. If you really want to match the color of the board.... Paint the repair with fingernail polish, lol.

Random epoxy might be fine but good luck finding a spec sheet to look up the conductivity. When using it to repair a PCB between traces on an amp I'd rather spend $15 and get the good stuff.

Anyways, very late but here are the after pics. Grinded out the burnt PCB sections with a dremmel, was slightly concave but filled it with the overcoat pen. Completely removed the traces that were closest to the burnt section and soldered in jumper wire to restore the connections. Hot glue to keep the jumper wire from vibrating loose.