Hello fellow DIYers, im wondering if someone could shed some light on a speaker protection circuit that is not engaging.
All output transistors have 8mv on the emitters so i have no shorts and it works if i mimic the final transistor to shunt half of the supply to the relay to ground.
The relay has +44v on each side, so im guessing once the final transistor has +0.6v on the base it will shunt one side to ground and enable the relay. However this transistor has 0v on the base, and im at a loss to what could be causing it.
Ive replaced all 4 diodes shown with new exact matches and also replaced the final 4 transistors (first 3 have 0V on the base, so these are not engaged). Voltages shown in the schematic are when the relay unlocks (half of what they are).
Any ideas?
All output transistors have 8mv on the emitters so i have no shorts and it works if i mimic the final transistor to shunt half of the supply to the relay to ground.
The relay has +44v on each side, so im guessing once the final transistor has +0.6v on the base it will shunt one side to ground and enable the relay. However this transistor has 0v on the base, and im at a loss to what could be causing it.
Ive replaced all 4 diodes shown with new exact matches and also replaced the final 4 transistors (first 3 have 0V on the base, so these are not engaged). Voltages shown in the schematic are when the relay unlocks (half of what they are).
Any ideas?
An externally hosted image should be here but it was not working when we last tested it.
[/url]Toshiba SA-7100 Manual - AM/FM Stereo Receiver - HiFi Engine
Service manual is there, however it has a few errors, namely Q805 is a 2SA841.
Service manual is there, however it has a few errors, namely Q805 is a 2SA841.
If that is one of the bias setting diodes then you may well find damage to the output stage. Based on that I suspect your relay fault will be down to the emitter resistors being open and the 'current limiting detect' part of the relay driver coming into play thinking there is a massive overload.
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