tuner repair problems

I recently acquired a Sansui T-80 am/fm tuner. The sound was pretty good,
but I had some flaky performance issues: The tuner would periodicaly lose
its' quartz-lock and the "tuned" inducator would drift badly. Also, the
entire digital display would periodically dim and lose some or all
functionality.

I opened up the case and first off noted that the main filter caps on the
power supply were leaky. Well, I figured, might as well bite the bullet and
replace all of the electrolytics given that this tuner was built in 1981.
So last night I replaced all 44 caps. I had trouble finding one of the spec
caps, a 0.15uF 100V electrolytic, and so ordered and installed two film caps
of this rating instead. All replacement caps matched the ratings of the
originals EXCEPT those 0.15uF caps... I think a previous owner had run into
the same problem with availability of this cap in an electrolytic and had
substituted a 0.22uF 100V.

I cleaned up the boards, put the whole unit back together and powered it up.
Well, first thing I noticed was the sound... low volume, tinny, no base at
all. Whereas before I started 25% volume on my amp would shake the house,
now I can easily go past 50% and still can't feel any thump in the floor.
The tuner drift issue has gone away, I suspect a cap labelled "AFC bias" was
the culprit there. However, I still have the dimming issue with the digital
display; perhaps the +5VDC regulator that powers the display board is flaky?
It's in a tough spot to blast with heat or cold without affecting a whole
whack of other components.

I left the tuner on all night thinking maybe there is some sort of initial
"burn-in" period and I THINK it sounded a bit better than at midnight last
night, but who knows...

Can anyone tell me where I might start to diagnose the tinny sound problem?
There are but a handful of coupling caps in the FM signal path, some in the
IF amp section, some adjacent to the MPX decoder. I am inclined to toss
back in the 0.22uF electrolytics that I replaced with film caps; they are
output coupling caps just to see what happens.

Any assistance greatly appreciated.

Dave



.

Relevant Pages

  • Re: "International" capacitors
    ... feel much better than Mallory and Sprague Atom in a Fender Blackface Twin, ... Printed on the caps: HTD: High Temperature Dynamics(for high ... temperature) Could this affect the feel and sound in a Fender Twin amp? ... They were typical japanese electrolytics of their day, ...
    (sci.electronics.repair)
  • tuner repair problem
    ... I recently acquired a Sansui T-80 am/fm tuner. ... replace all of the electrolytics given that this tuner was built in 1981. ... So last night I replaced all 44 caps. ... first thing I noticed was the sound... ...
    (sci.electronics.repair)
  • Re: anothr ant tuner question
    ... >touching around the tuner anywhere doesn't alter anything. ... It could indicate that the caps have a somewhat "sticky" bearing ... If the rotor and stator ... greater mesh (more capacitance, lower reactance). ...
    (rec.radio.amateur.antenna)
  • Re: B&O VX5500 VCR, bad picture
    ... > When your VX starts to have bad pic/sound via tuner, change all caps ... > When your VX starts to have problem synchronising in PB/REC change all ... When I switch the VX on or off, I have a correct picture on the screen ... No sound from tuner. ...
    (sci.electronics.repair)
  • Re: B&O VX5500 VCR, bad picture
    ... When your VX starts to have bad pic/sound via tuner, change all caps ... caps on bottom PCB ...
    (sci.electronics.repair)