Hi.

This is an odd fault. The way the circuit works, the SAA7705 produces four independent 1V P-P signals. These are amplified by a pair of INA2137 dual amp ICs to 4V P-P, filtered, and sent to the connector. They have floating grounds, which are bonded to real ground at the connector. I thought at first it might be the left ground that was faulty, but having checked the circuit diagrams to refresh my memory, the two ground pins are in fact front and rear, not left and right. So if one was bad you'd lose either the front or rear outputs, not the left or right.

The line level outputs are tapped off before the INA2137s and separately filtered, then go to their own connectors.

If one INA2137 had failed, for whatever reason, again you wuold have both front or both rear outputs go bad. For both front and rear left channels to go down, BOTH chips would require a simultaneous, identical partial failure. Not likely. Similarly, either before or after the amps, each channel has it's own separate circuit, so there is no single point of failure. The same thing would have to go wrong in two different places as far as I can work out.

Since the line outs work, it proves the SAA7705 is ok. Since the right outputs work, it proves that both INA2137s are basically good, AND that both grounds are ok.

We need to find something that is common to both left channels. From a hardware standpoint there isn't really a good candidate.

Hmm. I'm going to have to think about this one.

One thing does come to mind, although it's pretty obvious. Have you tried swapping the left and right inputs to your amplifier? It may be nothing to do with the empeg at all.

Pca