Quote from: Tassieviking on April 05, 2023, 10:20:12 AMHere is the 3210 issue 7 schematic if it helps.
It is a lot clearer then the issue 2 schematic but there are most likely differences somewhere.

That is a far better schematic, but the component values are definitely different.

I tested a couple of them quickly last time I turned it on, and they seemed normal temperature. The two hot resistors I could feel a few inches away from the board. I will check it out again.

The clean channel on the amp works nicely, but on the lead channel, the signal is barely discernible out of the speakers. I see R46 and 47 look burnt on the board, and R67 and 68 look like the wrap on the resistor has cracked due to old age.

On the schematic c38 and 39 are marked to be 10 uf, but I have 100s in there, and c40 and 41 on the schematic are 47 uf, but 68s are installed. I cannot read the resistor values for R44 45 46 47...

I do have a good meter, and scope. Any suggestions would be appreciated.

When checking v+ ground to pin 1 on IC1, the lead channel will kick on as long as I have the positive lead touching the pin from my meter. Next thing to check?Plz keep a bit layman, was years ago that I took digital repair 😂

Also I'm reading 40 volts DC across resistors 46 and 47 which are getting incredibly hot, 6 volts across resistors 44 and 45. The zeners looked to test okay, and I see no problems with the caps there. When I do click on the overdrive channel, the LED on the front comes on very very dimly.

Just got one of these and a 60's 4x12 cabinet for $125, but the lead channel is extremely quiet. I can hear that it has the crunch, so I know that part of the circuit is good.


The amp does not respond to the volume knob on the lead channel, so I'm expecting it's a problem with the pot.

If turns out not to be the volume pot, what other components could cause that pot not to respond on the lead channel?

Also, what would be some good mods that I could add that I can make switchable with installing switches on the front plate?

I did not see any cold joints or cracked traces before replacing the transistors, but I did not try to reflow the joints either. I did fully test after replacing Q1 and got the same results. I will try to find time tonight to get some post-repair voltage readings for comparison. Any suggested test points would be appreciated

   I can stand by my voltage readings +-.5v or so (I have a crappy meter). I replaced Q2 1st but got no results. Replacing Q1 did the trick. One other symptom that I did not mention is with the crunch channel all the way down, (gain and volume) a signal could still be heard if the clean vol. was over 5 or so. I suspect the transistor must have been 'leaky' and not 'burnt' enough to shunt the channel.

Turns out it was Q1 at fault - Nice to have a clean channel again

Great explanation- I ordered a cheap pack of j111's from eBay. Thanks all for the help.  :dbtu:

   The voltage changes polarity correctly when switched from -13 to +13. The voltage immediately after the 1mrg resistor changes from -6.5v to +6.5. Shorting Q1 seems to mute the crunch channel. With the switch in or out, the clean volume has some effect on the overall volume output if adjusted.

The +-13v drops down to about 6.5v after R54 and is present at the diodes. since the crunch channel is always on should I assume Q1 to be bad?

I have a Frontman 25r amp and the drive select does not work from the switch or the footpedal. The crunch channel is always on. I tested the pedal and the switch for continuity, and both work fine. Any suggestions on troubleshooting this problem?

An added note- The LED indicator DOES respond then to switch is depressed, but the amp still stays on the crunch channel.

Schematic is attached

Thanks!