HK 75+ Receiver Repair

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ledge

New member
Joined
Apr 22, 2015
Messages
4
Location
LI NY
Hello all, my name is Ledge I am the proud owner of a Harman Kardon 75+ that has served me well many years purchased new in 1973. I have been using it with the Right back and the front left. The front left just gave up too with pops and noises. I replaced all the Electrolytic caps on the amp modules with nichicon muse, Qty-3 47uf and qty-2 220uf caps. hoping that would repair my problem, it did not. I do have the schematic and was hoping somebody could please chime in. i read the MV on the speaker terminals i read RF+ 73.2, LF= 88.5 and raises up, LR + 35.5. RR= 3.0 1.5 7.1 highest this channel works great. My left front has alot of pops and static. Can anybody please give me some insight on this and what I should do next. Are there any known problems or parts on the amp boards that I could check out. Thank you for any advise. Regards Ledge
 
You are using it as a stereo amp? Did the other two channels stop working first? The DC offset you are seeing on the outputs is likely due to leaky transistors, and they could conceivably cause pops. I've seen this on other HK stuff, the phono pre on a 330C. This old gear needs more and more parts as time goes by.
 
You are using it as a stereo amp? Did the other two channels stop working first? The DC offset you are seeing on the outputs is likely due to leaky transistors, and they could conceivably cause pops. I've seen this on other HK stuff, the phono pre on a 330C. This old gear needs more and more parts as time goes by.

Thank you quadseacher, yes I have been using the RR and the Left front as a stereo unit. The left front just went out 2 months ago. I was thinking wrong and thought the caps would cause popping & noises. All the old caps looked good but I do not have an ESR meter. I left the working channel alone RR and did not replace the caps. I do have them. I did not realise trannies could leak. I can only measure emitter to collector and base for shorts. Can u tell a leaking trannie with a volt meter?? I think there are about 6 transistors per module besides the Driver? Trannies 2 attached to the heat sink. I am going to have to pull a module to get part #'s and then wing it with known trannies that are problem causes. I do not have a scope and there is no way to T/S these in the receiver cannot get to the lands or pins. I gather 4moretech who worked on these had a way to T/S these on the bench. I gather the Driver trannies could also be leaking?? 2 of the bad channels have low volume and slight popping. The left front has normal volume but really bad popping that I do not want to blow a KLH model 17. Thank you again, when I have time I will get trannie #'s. I was hoping for the best but the caps changed nothing, but had to be done being 40 years old . Regards Ledge
 
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