Harmon-Kardon 75+ FM issue

[smitherman]

So I picked one of these up to use as a bedroom system. Its a quadrophonic receiver but you can set if for 2 channel only operation. Got the manual, set the switch to stereo and have been using with a my dynacos for 6 months or so. I use the Aux for my ipod and FM for npr in the morning, last week the FM totally dropped it seemed.

The tuning indicator still shows i am pulling in the stations, but i have to crank the volume way up to barely hear the voices. AM works adn all the other inputs are fine. Cleaned all the switches with deoxit but still the same issue. Also use the muting controls on the back to set muting levels but the problem persists.

Any other ideas to trouble shoot, love this thing but if the FM doesn't work have to retire it, it is the only reason the wife let the dynacos upstairs

 

[smitherman]

Ok, so hooked up a TT to test that input and it played for about 30 secs then the left channel dropped and then the right pretty quick after that. Now both phono inputs are the same as the FM ones, AM and Aux are ok for now. Any ideas of what to look at?
fuses seem fine and saw obvious signs of failure (smoke, popping, etc)

thx
Scott

 

[blhagstrom]

Got one myself that I've been working on.

Check the power supply. The two regulators are mounted pretty weird. Bolted to the chassis but only surface soldered to the board.

Phono may be caps in the pre-amp board. (I recapped mine and changed all the transistors).

You DO know that the pre-amp and quad decoder just plug into a large connector, right? Try pulling those boards and de-oxit the connections there.

I changed all my main filter caps and rebuilt the PS. My FM is "slow" to start. Weird. Probably need to recap the tuner.....

 

[Livin4]

I'm in the process of restoring one also, finished re-caping it and found the pre had issues. I’m just waiting on new transistors for the pre-amp board. The signal starts clipping at very low volumes, and I traced it back there. When I get that part sorted out, I will be doing a tuner alignment.

....(I recapped mine and changed all the transistors)...

BLHAGSTROM, What did you use for the transistors on the pre?


It looks like the tuner is being run off of the 12V supply (Q904) and the phono and pre-amp sections are run from the 30V supply (Q902), the 12V is also derived from the 30V supply.

The Phono and pre-amp are on the same board, and they get their power from the same wire, orange I think. It daisy chains around the connector the board plugs into. So, I'm not sure why your aux inputs would work and your pre does not. Unless the 30V is way low, below what the phono amps need (IC 701 & 801).

It looks like both of the tuners run off the 12V, so it's odd that your AM works, and FM doesn’t. That would almost point to the selector switch that switches the power to the tuner.

Check the power supply. The two regulators are mounted pretty weird. Bolted to the chassis but only surface soldered to the board.

I agree, check these and see if something is bad.

You DO know that the pre-amp and quad decoder just plug into a large connector, right? Try pulling those boards and de-oxit the connections there.

And this. Also, try the FM Muting switch.

EDIT: I just re-read your first post, you get sound from the tuner, but only with the volume all the way up. You say you use the AUX for your Ipod? Not Tape Mon1 or 2? The manual shows a direct connection from the FM, AM, AUX, and phono pre to the function switch. From there the signal goes through the tape mon1 then tape mon2 switches. If your AM, and AUX works, but not the FM or phono, I would try to use some deoxit on the function switch.

 

[smitherman]

Yeah, seemed weird to have am but not fm. Will redo the cleaning on that switch this weekend.

thanks for the ideas!

 

[blhagstrom]

BLHAGSTROM, What did you use for the transistors on the pre?

Fairchild KSC1845. The 2SC693 crosses to KSC945 and now I don't remember how I came up with KSC1845 (I had those on hand). The manual says you can use 2n3417.

:headscrat works...

 

[Livin4]

Yeah, seemed weird to have am but not fm. Will redo the cleaning on that switch this weekend.

thanks for the ideas!

Also might be in the FM muting, but that still won't explain the phono section.. :scratch2:

Fairchild KSC1845. The 2SC693 crosses to KSC945 and now I don't remember how I came up with KSC1845 (I had those on hand). The manual says you can use 2n3417.

:headscrat works...

Cool, I ordered KSC1845's I found it listed as a cross in another thread.

 

[blhagstrom]

Must be where I picked up on it.
I checked the specs. KSC1845 are higher rating all around. Probably overkill but I think they are way cheaper (like 0.06 is much different than 0.20).

I picked up this 75+ cheap just to have something to tinker with.
I did re-cap all the filter caps and rebuild the PS but the FM is still slow to fire up. Almost like a tube radio.

Again :headscrat