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Help with Harman Kardon Citation 22 amplifier repair

You can see the service manual here:

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The problem is no audio from the right channel. The problem occurred after a lightning-induced power surge so I assume that was the cause. I expecte d to find bad output transistors but that was not the case. I believe the problem is not related to the protection circuit as I removed Q402 and disc onnected 2 leads from Q418 (there is a brief description of the protection circuit on page 4 of the manual).

With an audio signal connected, I can see the the signal at Q404 & Q412 mat ching the left channel. At Q406 & Q458 the signal is gone.

Measuring some voltages I found Q420 to have -81V (E), -80V (B), +81V (C) c ompared to -6.7V (E), -6.1V (B), -6.4V (C) for Q419 on the left channel. A lso, the +/-1.2V on the collectors of Q422, Q426, Q424, & Q428 is not there and I cannot figure out where it is supposed to come from. Note that the rail voltages measure about 80V as opposed to the ~58V shown on the print ( that is only for the Japan model I think).

Suggestions?

Reply to
jackjohnson2244
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Check D402 (zener) section and make sure you have 13.8 volts on that rail.

Reply to
Maynard A. Philbrook Jr.

On Thursday, November 28, 2013 5:52:25 PM UTC-6, Maynard A. Philbrook Jr. w rote:

fter a lightning-induced power surge so I assume that was the cause. I exp ected to find bad output transistors but that was not the case. I believe the problem is not related to the protection circuit as I removed Q402 and disconnected 2 leads from Q418 (there is a brief description of the protect ion circuit on page 4 of the manual).

matching the left channel. At Q406 & Q458 the signal is gone.

C) compared to -6.7V (E), -6.1V (B), -6.4V (C) for Q419 on the left channel . Also, the +/-1.2V on the collectors of Q422, Q426, Q424, & Q428 is not t here and I cannot figure out where it is supposed to come from. Note that the rail voltages measure about 80V as opposed to the ~58V shown on the pri nt (that is only for the Japan model I think).

The +/-13V and 23V off the zener diodes all look good.

Reply to
jackjohnson2244

would suspect FETs first as they seem to hate high dV/dt the most

Reply to
N_Cook

fter a lightning-induced power surge so I assume that was the cause. I exp ected to find bad output transistors but that was not the case. I believe the problem is not related to the protection circuit as I removed Q402 and disconnected 2 leads from Q418 (there is a brief description of the protect ion circuit on page 4 of the manual).

matching the left channel. At Q406 & Q458 the signal is gone.

C) compared to -6.7V (E), -6.1V (B), -6.4V (C) for Q419 on the left channel . Also, the +/-1.2V on the collectors of Q422, Q426, Q424, & Q428 is not t here and I cannot figure out where it is supposed to come from. Note that the rail voltages measure about 80V as opposed to the ~58V shown on the pri nt (that is only for the Japan model I think).

Thanks for the suggestions. I had started looking at this a while ago and put it to the side. It turns out that I had removed one side of a jumper w ire to make a resistance measurement or something and it was still disconne cted. Replacing the connection brought the voltages back to normal and bro ught the audio back. It was Q402 that was bad.

Reply to
jackjohnson2244

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