Help with Harman Kardon Citation 22 amplifier repair

You can see the service manual here: http://manuals.harman.com/hk/Service%20Manual/citation22%20sm.pdf

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 expected 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 protection circuit on page 4 of the manual).

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

Measuring some voltages I found Q420 to have -81V (E), -80V (B), +81V (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 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?

 

[Maynard A. Philbrook Jr.]

In article <2081169e-751f-4216-a146-4b164f09bcbf@googlegroups.com>,
jackjohnson2244@gmail.com says...

You can see the service manual here: http://manuals.harman.com/hk/Service%20Manual/citation22%20sm.pdf

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 expected 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 protection circuit on page 4 of the manual).

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

Measuring some voltages I found Q420 to have -81V (E), -80V (B), +81V (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 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?

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

 

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

In article <2081169e-751f-4216-a146-4b164f09bcbf@googlegroups.com>,

jackjohnson2244@gmail.com says...



You can see the service manual here: http://manuals.harman.com/hk/Service%20Manual/citation22%20sm.pdf



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 expected 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 protection circuit on page 4 of the manual).



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



Measuring some voltages I found Q420 to have -81V (E), -80V (B), +81V (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 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?



Check D402 (zener) section and make sure you have 13.8 volts on that

rail.

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

 

[N_Cook]

On 28/11/2013 23:03, jackjohnson2244@gmail.com wrote:

You can see the service manual here: http://manuals.harman.com/hk/Service%20Manual/citation22%20sm.pdf

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 expected 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 protection circuit on page 4 of the manual).

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

Measuring some voltages I found Q420 to have -81V (E), -80V (B), +81V (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 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?

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

 

On Friday, November 29, 2013 9:25:55 AM UTC-6, N_Cook wrote:

On 28/11/2013 23:03, jackjohnson2244@gmail.com wrote:

You can see the service manual here: http://manuals.harman.com/hk/Service%20Manual/citation22%20sm.pdf



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 expected 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 protection circuit on page 4 of the manual).



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



Measuring some voltages I found Q420 to have -81V (E), -80V (B), +81V (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 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?





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

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 wire to make a resistance measurement or something and it was still disconnected. Replacing the connection brought the voltages back to normal and brought the audio back. It was Q402 that was bad.