I have a Carver TFM-4.0, which is the same as the M4.0t and very similar to the TFM-42 and TFM45. The left channel is about 5-10dbs stronger then the right. I checked the amp boards and the components are within a couple of ohms of each other. Neither channel is offset more than 15mv.
I studied the schematic, and there is an op amp (to invert the signal for bridging) only on the left channel, not the right, which I find a very odd design. It seems strange to me that carver didn't use an identical design for each channel and put active circuitry in one channel but not the other. Basically, for the right channel, the signal goes straight through to the amp board, but for the left it goes through an op amp first. In my case the left channel has more gain than the right. I swapped out the op amp with a new one to see what would happen, but the problem remains.
The other thing I noticed it that there is a FET that is supposed to mute the signal (part of the protection) on each amp board at the beginning of the signal path. I did check using a transistor/FET checker and it seems good.
Anyone have any suggestions for where the problem might be?