Fisher 200T receiver speaker hum, one channel

[pwreimers]

I am hoping to understand my Fisher receiver. It's never been repaired by anybody besides me, to my knowledge; it was my Dad's and he purchased it around '65. The stereo beacon lamp stopped working, along with a lamp on the tuner slider, the one showing the stations. I was able to repair those fairly easily.

The receiver is fully functional, with some oddities (headphone left/right appears reversed, muting toggle switch is non-functional).

What I am inquiring about is that the right channel has speaker hum, and not the left, and increases with volume increase. The hum is not present when a record is playing (between tracks and quiet passages) and is only present when it is 'idle' (waiting for me to begin another record).

I can easily live with this, as the hum is relatively faint. If this is normal, I have no problem. But, if this is indicative of something I should pay attention to, and there is a way to troubleshoot and repair this I'd like to do that when I have some time.

Do you have any advice for me?

Regards,
Pete

 

[bberkom]

Does it happen on all inputs or only when using the phono input? If it is only when using phono and goes away with a record playing, I would suspect some sort of issue with the cartridge or headshell connections for the right channel.

 

[larryderouin]

Pete; I think you got a little brain finger disconnect there. If your dad bought it around 65 the unit would be a 220-T that came out in mid late 65 for the '66 model year. (Think car model years for audio which is Sept to Aug). It was the baby of the 220-T,500-T,550-T,700-T series. They stayed in production for 2-3 years IIRC.

If it looks like this it's a 220-T

This is a 200-T from about 1969-70.

Both units are roughly 20W EIA (total peak) or about 7watts RMS. But no matter, either one is a decent unit. Both are capacitor coupled which means that a load (speaker (cheap one for testing) or a dummy load) has to be connected to the speaker terminals when taking offset readings are the spkr terminals. Ideally it should be 0.0VAC with no DC (with load connected.)

Listen to the hum and compare to 60HZ hum and a 120Hz(1octave higher) and tell us what it is.

 

[pwreimers]

Does it happen on all inputs or only when using the phono input? If it is only when using phono and goes away with a record playing, I would suspect some sort of issue with the cartridge or headshell connections for the right channel.

You're absolutely right. Thanks for the tip.
Those darn Dual headshells...gotta keep them clean.

 

[pwreimers]

Pete; I think you got a little brain finger disconnect there. If your dad bought it around 65 the unit would be a 220-T that came out in mid late 65 for the '66 model year. (Think car model years for audio which is Sept to Aug). It was the baby of the 220-T,500-T,550-T,700-T series. They stayed in production for 2-3 years IIRC.

If it looks like this it's a 220-T

This is a 200-T from about 1969-70.

Both units are roughly 20W EIA (total peak) or about 7watts RMS. But no matter, either one is a decent unit. Both are capacitor coupled which means that a load (speaker (cheap one for testing) or a dummy load) has to be connected to the speaker terminals when taking offset readings are the spkr terminals. Ideally it should be 0.0VAC with no DC (with load connected.)

Listen to the hum and compare to 60HZ hum and a 120Hz(1octave higher) and tell us what it is.

Thanks Larry! I was 17, and should know better. My memory...
Pete

 

[bberkom]

You're absolutely right. Thanks for the tip.
Those darn Dual headshells...gotta keep them clean.

A Dual you say? My money is on the muting switch. This mutes the output when the turntable is not running. If it's dirty, it can sometimes cause a hum and probably just needs cleaning.

 

[pwreimers]

A Dual you say? My money is on the muting switch. This mutes the output when the turntable is not running. If it's dirty, it can sometimes cause a hum and probably just needs cleaning.

Thanks again. I'll just turn it over and give it a look-see.
Could easily be. There was a bit of the cam grease on that switch. The best I could do was swab it with some isopropyl and so far, it's good.
Pete

 

[pwreimers]

I can't believe it, chasing this creature!

It turned out to be the RCA four-prong connection was intermittent! Well, it appears that way now. I've been wrong thinking I had it right too many times to be confident.

Hours...sometimes I just have to shake my head...and swear a blue streak.

 

[fred soop]

I had a similar issue with a Dual 506. RCA connectors had not actually gone bad but they were rather cheap connectors. I replaced with a higher quality and the long run to the preamp is custom build to length Blue Jeans Cable with a very low capacitance and industrial strength connectors. Also, make sure the separate ground wire from the turntable is connected to the amplifier chassis, NOT the signal cable shield.

As for your comment above regarding headphones, this keeps coming up. The old standard was right channel on the tip of the connector. That was changed sometime during the 1970s, so all of the vintage Fisher (and other manufacturers) headphone jacks are reversed. Just swap wires at the jack and you'll be compatible with all recently produced headphones (and even Larrys late 60s PRO-4).

 

[pwreimers]

Upon further reflection, honestly I am embarrassed. Thank you for your time and thoughts, but...I apologize.

It's a REAL requirement to examine the full checklist, which in this case includes the cable connections. The embarrassment is because, too many times, I don't include (examine) my assumptions of what is I think is correct, examine them to be sure the assumptions are right, THEN proceed.

Tail betwixt my legs,
Pete

 

[larryderouin]

Pete; Don't knock yourself too hard. We've all BTDT before too. And we ALL learn from it. Some more easily than others (me included!).

Just for FYI! The muting switch on the 220-T has to do with inter-station hiss in FM when changing stations and weeding out weak stations. It has a set signal strength level and if a signal is below the set level, the circuit mute's it and only lets in those who's signal strength is above it. Start at 87.9 on FM with the muting off, go up the dial to 107.9 and note how many stations and all the hiss between them. When you get to the other end(107.9), turn on mute and dial back down to 88.1 noting the noise level and how many stations get past the muting gate. There may be a big difference.

Larry

 

[pwreimers]

Pete; Don't knock yourself too hard. We've all BTDT before too. And we ALL learn from it. Some more easily than others (me included!).

Just for FYI! The muting switch on the 220-T has to do with inter-station hiss in FM when changing stations and weeding out weak stations. It has a set signal strength level and if a signal is below the set level, the circuit mute's it and only lets in those who's signal strength is above it. Start at 87.9 on FM with the muting off, go up the dial to 107.9 and note how many stations and all the hiss between them. When you get to the other end(107.9), turn on mute and dial back down to 88.1 noting the noise level and how many stations get past the muting gate. There may be a big difference.

Larry

Larry, thanks. It sounds like you can relate to overlooking the obvious, until it bites. It definitely bites.

Re: mute switch. I tried it, but did not see much of an impact on station tuning of weak signals with the switch on/off. I tried the tuning up the scale and down and saw little difference. Weak stations came through both ways and I wasn't sure how to count them!
Pete

 

[larryderouin]

Break out the DeOxit (D-5) and Faderlube (F-5) and go thru all of the switches and pots. You might have to do them multiple times before you get good results. DeOxit breaks down the bond between the sulphates (black crap) on the contact and the contact itself. 1st application spray it in the switch and move the switch 2-3 times to spread it around good (same with pots). Then let it sit for a 1/2 hour or so. Then give each a short shot and exercise the hell out of them (40-50 times and vigorously). Then use the faderlube on them to lubricate and leave some active cleaner in there. Do this every year or sooner if the environment is degrading the switches and pots from the salt.

But I suspect it probably needs an alignment. A better antenna will help some too, but I suspect an alignment will do a lot for it.

 

[pwreimers]

Break out the DeOxit (D-5) and Faderlube (F-5)...

But I suspect it probably needs an alignment. A better antenna will help some too, but I suspect an alignment will do a lot for it.

I can easily go through this with the products, as I purchased them for prior projects. Thanks for this idea and the technique! I know it's a good idea, and will help matters. After that, I'll give the tuner mute circuit another try.

An alignment? I have not heard of this before. I see a process in the service manual, but I'm not even close to being able to accomplish this as I don't have the equipment.
Is this your meaning?

 

[larryderouin]

Exactly. It'll have to be done at a shop that does radio work. Make sure they are familiar with 60's FM radios and tuners. And if so send a copy of the manual with it.

 

[pwreimers]

Break out the DeOxit (D-5) and Faderlube (F-5) and go thru all of the switches and pots. You might have to do them multiple times before you get good results....
But I suspect it probably needs an alignment. A better antenna will help some too, but I suspect an alignment will do a lot for it.

Larry,

I saved this chore for a time when I had some spare time, which is seldom. Most times I do this kind of thing because I need to, and sure enough, I needed to. I'd married two non-fully-functioning cassette decks into one and finished calibrating the good one. It sounds excellent through headphones but awful when hooked up to the Fisher 200T.

So, I took the receiver apart, followed your guidance with the DeOxit products. I also discovered why the fuse was wonky and fixed that while it's open. I'll have to wait until morning, as the fuse fix involves silver epoxy.

I can't believe how awful the cassette deck sounds. The phono sounds all right... Any idea? Does the alignment process affect anything else besides the FM tuning?

Thanks,
Pete

edit: I tried using the AUX inputs, both HI and LOW. The sound was right, so I figured the electronic circuits are okay. Upon switching back to MONITOR input, I notice the connection is a little funny. I wiggled it and got good sound, so I'll look at that when I reassemble it.

Nice to have the lube in there. The BASS and TREBLE work much better.

 

[larryderouin]

Unless you plan on recording you can just use the AUX for cassette input to the 220-T. The REC OUT is always on. The tape monitor is really used for 3 head Reel to Reel Decks so you can monitor what you are recording. Depending on where it inputs it's level can be the same or lower than AUX,

 

[pwreimers]

Okay. That makes good sense, too.

I switched back to the monitor, finding that my 'calibration' is a stopwatch and a pre-recorded tape. I only have two: Ann Peebles Straight from the Heart and John Hiatt Little Head. I chose John and probably shouldn't due to his vocals being twangy at the correct tape speed. I got it close, but not close enough! So, I played the tape with it running and adjusted the motor speed 'live' until it sounded right. THEN I timed his recording, and am within 2 seconds over nearly 5 minutes. It sounds better. That adjustment screw is so finicky...I hate to move it from the current setpoint!

I'll go back to the AUX input next.

Thank you for the help and information, Larry.