Fisher RS-1040 Receiver: no stereo from tuner?

[Kiwanda88]

I recently picked up a clean RS-1040 from a pawnshop for $6. Cleaned it up today and it's in pretty good shape; had to clean out some dust, clean the pots, and restring the tuner dial cord, plus the expected cosmetic work. I powered it up and everything works fine with one exception: it appears to only get mono from the FM tuner. No stereo light, no stereo image, though there's a strong signal on many local stations. I do get proper stereo imaging from the other sources so it's clearly a tuner issue.

Any ideas on where to start checking? I blew the (very light) dust off the tuning fins but otherwise did not touch the tuner when cleaning.

Thanks,

Erik

 

[larryderouin]

1st off what's your skill level and equipment T.O.& E.? Tuner's and Multiplex require specialized equipment, and skills (especially later Solid State gear). The tuners (both AM and FM) are chip driven, as is the Multiplex Decoder. Take the Stereo Lamp out of circuit and make sure it's operable (use an ohmmeter to check for continuity) as in a lot of these the lamp is a part of the circuit in that if the lamp goes out, you lose STEREO. If the lamp is OK, there isn't much of anything else you can do with just a DMM except voltage checks. Check all INTERNAL FUSES WITH THE METER for continuity. A visual won't cut it. Get what's left of the Manual off HIFI-ENGINE and check the voltages of the chip pins against the sheet. Do the checks with the tuner in MONO, and again with it set in Stereo. Write them all down and list them vertically by chip, in 3 columns (schematic, Mono, Stereo). Then we can see what's what. Also determine where the B+ voltages come in to the board and correlate them with the unit. Check them in MONO and STEREO modes. Also check the voltages off the power supply against the manual.


These(chips) may be proprietary and hard to source. You'll need a Signal Generator, an O-Scope, plastic tweakers, and a frequency meter at minimum to align the tuner. Best to leave it to a shop to troubleshoot.

 

[f0427ea]

I agree with Larry , if voltages aren't right nothing works right . If everything Larry has detailed checks out o.k. one more thing to ad is trim pots on the boards get cruddy just as do the switches and dials . I've got a 404 that was having F.M. stereo issues (excellent reception , no stereo separation) tracked it down to the MPX OSC adjustment pot , a little , gentle turning , rocking of the pot back and forth broke through the oxidation , brought back the stereo separation , has been fine since. Try tapping around on the p.c. board lightly (with something non-metallic) a lot of the problems I've seen in old equipment (I'm sure Larry will attest to this) is loss of connections be it due to pots , switches or solder connections. Just one more thing to try , especially when the funds aren't there to have it serviced proper by a tech.