My first post from an old timer.
I see here that this is a common problem with these Dynacord powered mixers. When the unit is powered on the protect led comes on straight away. I immediately checked the O/P transistors and removed them from the board (heat sink paste dried out so not a waste of time). All checked out OK. The main 80v + and - OK. However when I check for voltage on the inductors going to the speakers (o/p transistors removed) I found -30v on L501 which is the right side channel. The left side inductor shows zero volts. Am I correct in thinking that the right side is the culprit on the negative side or is this the correct approach in localizing the problem. I did cold checks on the other transistors and diodes (in-circuit) in this area and the appear fine. If I remove CN1 plug which drives the protect led on the mixer board it goes out. I did read somewhere on this site about some TL072 op amps causing a DC imbalance resulting in a similar action. I have attached the schematic diagram. A block diagram would be a help but I couldn't find one. Any guidance is appreciated.
I see here that this is a common problem with these Dynacord powered mixers. When the unit is powered on the protect led comes on straight away. I immediately checked the O/P transistors and removed them from the board (heat sink paste dried out so not a waste of time). All checked out OK. The main 80v + and - OK. However when I check for voltage on the inductors going to the speakers (o/p transistors removed) I found -30v on L501 which is the right side channel. The left side inductor shows zero volts. Am I correct in thinking that the right side is the culprit on the negative side or is this the correct approach in localizing the problem. I did cold checks on the other transistors and diodes (in-circuit) in this area and the appear fine. If I remove CN1 plug which drives the protect led on the mixer board it goes out. I did read somewhere on this site about some TL072 op amps causing a DC imbalance resulting in a similar action. I have attached the schematic diagram. A block diagram would be a help but I couldn't find one. Any guidance is appreciated.
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