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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Help with Harman Kardon Citation 22 amplifier repair
You can see the service manual he http://manuals.harman.com/hk/Service...ion22%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? |
#3
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Help with Harman Kardon Citation 22 amplifier repair
On Thursday, November 28, 2013 5:52:25 PM UTC-6, Maynard A. Philbrook Jr. wrote:
In article , says... You can see the service manual he http://manuals.harman.com/hk/Service...ion22%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. |
#4
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Help with Harman Kardon Citation 22 amplifier repair
On 28/11/2013 23:03, wrote:
You can see the service manual he http://manuals.harman.com/hk/Service...ion22%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 |
#5
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Help with Harman Kardon Citation 22 amplifier repair
On Friday, November 29, 2013 9:25:55 AM UTC-6, N_Cook wrote:
On 28/11/2013 23:03, wrote: You can see the service manual he http://manuals.harman.com/hk/Service...ion22%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. |
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