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Need help solving problem with HK1400 Amplifier - RH channel no sound

Having replaced faulty components in the stabilised supply to the preamplifier section of this Harman-Kardon amplifier, I found that the RH Channel was quiet, then discovered that the voltage on the collectors of Q414 &434 was at +27v instead of the +12v on the corresponding point in the working channel. None of the fusible resistors(R418,430, 442, 428, 444, etc., etc., were o/c or otherwise faulty, and all relevant transistors check out OK 'cold'. The rail voltages are correct, and the centre voltages measured wrt ground at R452/452 are virtually zero, so no DC offset. Can anyone suggest what component(s) may be responsible for this fault, which results in very quiet sound if a 1kHz s/w signal is injected at any early stage in the circuit, please?



Re: Need help solving problem with HK1400 Amplifier - RH ...

check d28-q410 circuit

Re: Need help solving problem with HK1400 Amplifier - RH ...

Since posting the above request, I have found that the 2SC3182 output transistor in the RH channel is s/c from base to collector and leaky between base and emitter, so this and it's companion 2SA1265 will both be replaced, although the latter device checks out OK 'cold'. Further checks are needed in case of other failures in this DC coupled design, but it seeems highly likely that the faulty output transistor was pulling up what should be a +12v line to +27v. As to what caused the failure, I don't know, but I was misled into thinking the fault wasn't in the output stage because there was 0v on the emitter resistors, as would be the case in a normally functioning amplifier. Oh, well, I've only been repairing radios and such like for 45 years!!! It has been suggested that all the preceding transistors - in this case there are 12 of them - in a DC Coupled amplifier, should be changed because of possible collateral damage caused by failure of the output transistors. This is of neccesity, time consuming, but, as the NPN output transistor failed short circuit base to collector, I may do this, assuming I either have, or can get, the transistor types involved, or known equivalents, amongst them, 2SC1775, 2SC2240, 2SD646,, 2SA970, & 2SB646. What do others think I should do?