Dead section of FM band on Sansui Stereo Receiver 661

Do the stations agree with the scale markings? ie someone restringed wrongly.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

What is the tuning mechanism, if it is a moving variable capacitor, maybe the plates are shorting, that would explain the deadness at the same points in the dial for both am and fm.

Spider webs and other things will goof up the tunning. I have one in the garage I use, i have to flip the tunning back and forth a few times before it will work at the low end on FM. The fact that its both AM and FM would seem to turn this theory off, but check it out. Does it have caps ??

greg

You don't have to be an Expert in electronics to repair equipment, but you certainly need a bit of knowledge and understanding of components and circuits. Rewinding coils is a last resort, and only in the event that you have positively identified that one is defective. First, what is your level of knowledge and experience in understanding and repairing circuits? What kind of test equipment do you have available? Can you use the equipment and understand what it's telling you? At a minimum, you should have a multimeter. A signal generator covering the FM and/or AM bands would be nice to have, as would a scope. In your situation, the signal generator and scope would be more useful than a multimeter. Since the unit works, apparently well, on the ends of the dial, you can probably rule out everything from the 1st IF through the audio outputs. That leaves the RF amp, the local oscillator(s) and the mixer(s). Check that the tuning capacitor plates aren't touching at any point in their travel. If any of the outside plates are bent outward, don't disturb them; just make sure that the rest are straight and not touching. Touching plates would explain the symptom that you described. You didn't say whether the unit is solid state or tube (valve) construction. That would be helpful to know. What's the model number of the unit?

on

That would be my guess as well...shorting could mean bent plates or foreign material (even dust) in the plates.

OP: look for a fairly large unit that moves with the tuning knob. It will be silver with a series of interwoven aluminum plates. They should mesh together without touching...even a little. Can be cleaned out with compressed air, or vacuum. Straightening is a little more finicky.

Careful: Fragile!

jak

Picture of the part described above:

It's the silver thing at the extreme left of the circuit board in the first picture.

Remove everything from "661" on, in the URL to get to the rest of the brochure. That's a pretty nice piece to get for free....

jak

"hr(bob) snipped-for-privacy@att.net" schrieb:

on

OTOH: The plate packets for FM tuning aren't the same as for AM tuning ...

And the distance between the FM plates is IMHO too big as there could be a short.

Just my 2 cents

Reinhard

Hi Everyone: Thanks so much for your help so far!

I opened up the unit and looked at the capacitor wings on the fm tuner. Didn't see anything touching or out of alignment.

Changes to my initial information:

1. The AM band is now working fine. Good signals. The frequency indicator is out of alignment with the stations but that can be lived with just fine because it is in alignment with the frequencies for the FM band which I'm more concerned about.

1. I plugged in headphones and tuned along the entire length of the FM band with the volume jacked all the way up. I CAN HEAR every station along the band. And I confirmed they're the right frequencies when compared with the digitially tuned walkman.

So it seems the problem is that most of the frequencies on the FM band are not being amplified whereas about 3 stations do come in at full amplification.

Any thoughts as to how I might proceed now would be appreciated. Thanks again!

Gord

One possibility, the ones you can get are mono, or too weak for it to switch to the stereo signals. And your stereo demodulator or the preamp or audio switch is bad.

Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)

After some further examination around with the receiver, I noticed a button on the front called, "FM Muting OFF". I pressed it. All of the stations were once again coming in strongly and clearly amplified.

Problem solved!

Thank you to everyone for your suggestions and help with diagnosing this situation!

Best Wishes,

Gord

FM muting is essentially a squelch function designed to mute the hiss between stations. It sounds like it is faulty or adjusted incorrectly. However, once your desired station is tuned in, it serves no purpose at all so you are perfectly OK leaving it off.

Pat

What Sansui do you have? On the Sansui TU-9500 the mute level can be adjusted on the back of the tuner. The AM stick antenna mounted on the back is tunable by sliding in and out.

maybe you need to hook the son of a bitch to an outdoor antenna?

Uh...do as I didn't; read the header.

Somehow, I got that this problem occurred on both AM & FM, hence advised that it must be a problem with the tuning cap. Reading again, I realized there was no mention of AM.

The problem (and model #) was succinctly stated in the subject header.

jak

Somebody posted the entire OP in another reply, and it apparently 'did' state that the problem occurred also on AM. (My news supplier purged the OP.) I guess the takeaway lesson is to read both the header and the body, then ask further questions if they don't agree.

So...did the problem also occur on AM? If so, how did pressing the FM mute button solve that?

jak

Hi Jak:

Initially thought the AM band was problematic as well. in a subsequent post I indicated the AM was fine, just the FM was un-amplified.

Needless to say, everything's great. Thanks for your help.

Gord