Dead section of FM band on Sansui Stereo Receiver 661

[[email protected]]

I just found an old discarded Sansui receiver. It works well in all
respects except a large middle section of the AM and FM band don't
receive any stations. A couple of stations on the extreme ends of each
band come in loud and clear, distortion free.

All other aspects of the receiver work fine.

Is there a way that I can fix the tuner section by re-winding coils or
something else I can try that's reasonably inexpensive. I am not an
electronics expert but I am open to any ideas.

Thanks,

Gord

 

[N_Cook]

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

 

[hr(bob) [email protected]]

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

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.

 

[GregS]

e.graffiti.net/diverse:graffiti.net/


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

 

[jakdedert]

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.

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

 

[jakdedert]

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:
<http://www.classicsansui.net/images/Literature/Receivers/661/661b.jpg>
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

 

[Reinhard Zwirner]

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.

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

 

[[email protected]]

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.

2. 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

 

[Mark Zenier]

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.

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 [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)

 

[[email protected]]

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

 

[jakdedert]

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.

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

 

[jakdedert]

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

 

[[email protected]]

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- Hide quoted text -

- Show quoted text -

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