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Old 26th July 2010, 09:32 PM   #1
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Default Harman Kardon 730 FM problems

Hi I am Ulf my nickname is Aron Living in Sweden and new to this forum. One hobby I got is that I started to collect Harman kardon recievers from the 70s.
I bought an unseen 730 harman kardon.
http://manuals.harman.com/hk/Service...hk730%20sm.pdf
When I powered it up I got aware of a problem I had distorsion in my right Channel when I had the radio on FM, so I thought it was the selector or one of the pushbuttons that was making this cause of corrosion in it. The tuning meter worked ok then.
I cleaned the buttons and the selector with aerosol spray.
Now when I start it I can barely hear the FM radio. The volume is very very low and I got some sort of a white noise in the background also.The tuning meter doesnt move any longer. Its like having a pillow in the speakersClick the image to open in full size.. Well The AM doesnt work either. a noise like there is a generator disturbing the reciever. Well But the PHONO WORKS AWESOME and the sound is GREAT there. I have no clue. PLEASE Give a hint where to start. I checked for loose soldering and contacts and lack of ground. I can handle an instrument but Iam not an electronic expert on component level.
PLEASE give a hintClick the image to open in full size.
Best rgards Aron
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Old 27th July 2010, 11:28 PM   #2
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As both AM and FM are defective I would first check if the B3 (+ 12,74 V) power supply to the RF front end/IF/MPX board is present. You can trace it from the supply/regulator board (Emitter of Q6 or point LP19) to the IF/MPX board (con. A12 and LP201) and the RF front end (pin 5). If B3 supply is missing or too low (less than 12V) suspect the pass transistor Q6 and associated components. (D5,...) If B3 is present the problem can be much more complex to trace and very likely beyond your knowledge. Repairing RF/IF circuits requires a good level of experience in electronics and specialized test equipment.
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Old 28th July 2010, 08:33 AM   #3
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Quote:
Originally Posted by Tubologic View Post
As both AM and FM are defective I would first check if the B3 (+ 12,74 V) power supply to the RF front end/IF/MPX board is present. You can trace it from the supply/regulator board (Emitter of Q6 or point LP19) to the IF/MPX board (con. A12 and LP201) and the RF front end (pin 5). If B3 supply is missing or too low (less than 12V) suspect the pass transistor Q6 and associated components. (D5,...) If B3 is present the problem can be much more complex to trace and very likely beyond your knowledge. Repairing RF/IF circuits requires a good level of experience in electronics and specialized test equipment.
Thanx. Yes the voltage is 12,1 volts. However the AM board works. I mean the volume is ok but it sounds like a generator disturbing it all over the band. Do u think the voltage is to low then? If so anything else I should think about cause I got a 1,5 ours drive to the dealer who sells a BD237 or 2N4923 or NTE 184 . Hope anyone should do? I cant find a 2sc1162(c) in Sweden.
Thanks for the reply
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Old 2nd August 2010, 02:06 PM   #4
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Thanks for ur advicedes it was the transistor on the subrectifier.the voltage is 12,6 v instead of 12v and I used a NTE184.
Also changed the electrolytic capacitors, rectifier diods and the zener and the sound is now AWESOME. Except that I think I gotta put a cheramic capacitor between the pream and FM ampl. Also changed all capacitors in the premap and sitch selector.
THANKS AGAIN I have one other amplifier I got a problem with is it possible to get an advice even there?Its a Harman kardon a-402. One of the main fuses blows after a minute and one channel gets extremely hot, the heatsink is like an owen! I suspect the q412 or can the vr 402 be set to a wrong value?
The owner before me trid to repair it and it looks like hell.
I cant find the 2sd415 or 2sb549 or 2sc853 on the market and absolutely no idea what I can use instead of 2sc1400.
I would be very Happy for an answer
Best regards
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