Need some help on a 2240B

[homebrew]

A while back I recapped the amps boards, power supply, and main filter caps. Everything worked fine. Today I replaced the bad "stereo" indicator light and recapped the phono board. In checking bias, DC offset, no problem. Set 8mV idle voltage in one channel. The other channel reads 0mV. What could be the problem? I hooked the receiver up and both channels work fine.

 

[Jailtime]

Can you adjust the idle voltage to 8mV with the trim pot? If so, will it hold steady for a long time? Maybe you just bumped the pot a little when you were working on it, they are very sensitive. Might as well start with something easy.

 

[homebrew]

The adjustment on the trim pot for the right channel has no effect on the idle current. But here's what I did. The left channel is exactly 8mV. So I measured the resistance of the trimmer and came up with 140 ohms. So I adjusted the right trimmer for 140 ohms. Probably not the right way to do it, but it's probably a lot closer than it was to the correct value. Another explanation, and it's probably the right one, is I'm having a brain fart and connecting the leads of my multimeter to the amp incorrectly. Fortunately there's no smoke, fire, or meltdown. I'm just going to set it aside for a while and come back to it.

 

[Jailtime]

I don't know anything else to fix your problem, but I can tell you to always measure resistance with the amp unplugged. It's for your safety and for your equipment, and to get the right reading.

 

[homebrew]

Thanks for the info. I did do the measurements with the receiver unplugged so I guess they're right as far as that goes.