I've got two vintage receivers with FM problems...

danny1968

New Member
Just picked up a Harman Kardon HK330A and a Sherwood S-7200 from Goodwill in pretty good shape. Both sound very good when the input is solid. But...

Both of these units have a decreased FM audio level and the Sherwood also loses the right channel when switched to FM input. Other inputs are louder and (on the Sherwood) in full stereo.

AM and Aux Input (cd player) seem to work very well (stereo and mono). Same results also when listening through headphones...

Question is: would a simple recap of the FM board (or multiplex) possibly fix this problem? I certainly don't want to inadvertently cause harm. Already went after knobs and selectors, but will also be going after switches with de-oxit...

Thanks for looking!
 
Those are probably alignment issues, though the dropping of one channel is odd. If you recap, touch only the aluminum electrolytics, nothing else. You might get lucky. Then find somebody to align them. You can't do it yourself without an alignment generator.
 
I'm using a 300 ohm dipole antenna...
fwiw, I test receivers regularly using the same antenna and have good to great results with other pieces...

cleaning switches w/ deoxit made no difference...
 
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...cleaning switches w/ deoxit made no difference...

There is more to clean. Look for the FM Oscillator trimmer usually located on the tuning gang. Also, the muting trimmer can lose contact to clean that one as well. Be sure to note the original position of the trimmers.
 
Thanks for your advice...
Though I've got some limited experience in reviving amps and receivers, I'm not yet familiar with the location of the fm osc trimmer... is that one of those mini-screwdriver adjustable 'pots' on the fm (or fm multiplex) board? or is the tuning gang the 'unit' that turns round when adjusting the station?

I gather your suggestion is to mark it's position, clean it with deoxit and return it to the original spot. Sound right?

Thanks!
 
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Thanks for your advice...
Though I've got some limited experience in reviving amps and receivers, I'm not yet familiar with the location of the fm osc trimmer... is that one of those mini-screwdriver adjustable 'pots' on the fm (or fm multiplex) board? or is the tuning gang the 'unit' that turns round when adjusting the station?

I gather your suggestion is to mark it's position, clean it with deoxit and return it to the original spot. Sound right?

Thanks!

You are correct. Some deoxit is not truly residue free, which is very important when spraying near the gang.

Please note, this is a "last ditch" technique before seeing your tech. This being said, my success rate it about three out of four.
 
Both of these units have a decreased FM audio level and the Sherwood also loses the right channel when switched to FM input. Other inputs are louder and (on the Sherwood) in full stereo.

The best observation would be to take the receiver to a place away from the rest of the bench equipment. Set up an Antenna to get a better estimate outdoors. Might be a simple screw adjustment as noted on the cap. Like set it up on the patio with a decent dipole and try vertical orientation of the ant. The signal strength meter is just an indicator. like when it moves to the plus side indicates the led's or analog meters are working. As for meters.. analogs are touchy. I've fixed a few with good rubies. Like surgery as repairing a watch.
 
H/K It's probably a transistor in the AF section of the tuner.
You should get the service manual and check the voltages on the transistors.
Hopefully the manual is available for download and lists the voltages as well as the B model.

Sherwood Check for broken wires to the selector switch.
 
One down, thanks to you...

The Harman Kardan HK330A fm now sounds nearly equal in volume to the other sources when switching between inputs. I marked and twisted 4 'pots' near the fm oscillator and took it outside to be sure of proper fm signal reception. Now I can tell the reception is in stereo, but the stereo lamp does not light. Old bulb was burnt, but new bulb does not light... sigh.

Have not yet had a chance to look at the Sherwood... definitely will check wires to selector as well as twist on the trimmer... sounds logical. I'll need to source a service manual to check transistors for this one...

Thanks!
 
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