I need Your help regarding send/return section of my amp.
The amp is a combo, solid-state Marshall 5212 Fifty Split Channel Reverb (it's around 30 yrs old). The sound is superb, both channels and reverb are working flawlessly to this day.
Recently, I decided to put my delay, reverb and chorus pedal into FX Loop, but when I do so, no sound is coming from the amp. I tried with different pedals (one at a time), with different cables, but no success. The whole time the guitar was connected to the direct input on the front panel (guitar>direct input>send>pedal input>pedal output>return). I strum the strings and nothing's coming out of the speakers. But then I noticed one thing, when I unplug the cable from the "Return" jack on the rear panel, the sound is coming up from the speakers like it's supposed to (without pedal involved ofc). It's almost like direct input on the front and FX loop section on the rear side can't be active at the same time... Is this common problem with these amps, do you have some advice on this issue, or should I take it to electrician to check it out?
Please check the label from the rear (below):
Thanks in advance!
Boston area currently.
Also who's a good repairman for these in the area.