Hi everyone... I'm trying to find a service manual or schematic for a Fisher RS-1035 receiver. I think the stereo decoder has a problem and needs some adjustment, but I'd rather have the specific procedure before I tackle this. I have enough test equipment to do the job, but no service info. This is for a good friend who has lost her job and is kind of strapped for funds, and I'm doing this "gratias". Any help would be greatly appreciated. Thanks! My email is r221b@juno.com.
sherlock
sherlock
Hi sherlock,
What is the number on the decoder chip (if it uses one)? I am assuming it's a newer model.
If this is the case, the adjustment is fairly easy. Set your stereo modulator / generator to a convenient frequency away from other stations and tune to it. Turn off the 19 KHz pilot and the modulation. You should now hear low level hiss. If you monitor the test point, it will should read close to 19 KHz, 38 KHz (rare) or 76 KHz (very common). Correct the frequency with the trim pot.
You're not done yet. The discriminator is normally out a bit. Set up to a place with zero or very low signal. Short the antenna signal out. If you have a signal meter, read the DC voltage. Use a small metallic tool and insert it into each discriminator coil (there are two, or top and bottom cores), the one that changes your reading the most is the one to adjust now. Using a plastic tool, align for as close to 0.0 mV as you can. Not done quite yet.
Send in a tone from your generator, no pilot. Remove your short and tune the set to this frequency. Connect your distortion analyzer to the tape output and read the distortion after you've set your levels. Carefully adjust the other core for the lowest distortion reading. Recheck your center tune voltage and repeat both steps as required.
Now the set will sound great compared to it's former self. Don't attempt this without the proper equipment.
-Chris
What is the number on the decoder chip (if it uses one)? I am assuming it's a newer model.
If this is the case, the adjustment is fairly easy. Set your stereo modulator / generator to a convenient frequency away from other stations and tune to it. Turn off the 19 KHz pilot and the modulation. You should now hear low level hiss. If you monitor the test point, it will should read close to 19 KHz, 38 KHz (rare) or 76 KHz (very common). Correct the frequency with the trim pot.
You're not done yet. The discriminator is normally out a bit. Set up to a place with zero or very low signal. Short the antenna signal out. If you have a signal meter, read the DC voltage. Use a small metallic tool and insert it into each discriminator coil (there are two, or top and bottom cores), the one that changes your reading the most is the one to adjust now. Using a plastic tool, align for as close to 0.0 mV as you can. Not done quite yet.
Send in a tone from your generator, no pilot. Remove your short and tune the set to this frequency. Connect your distortion analyzer to the tape output and read the distortion after you've set your levels. Carefully adjust the other core for the lowest distortion reading. Recheck your center tune voltage and repeat both steps as required.
Now the set will sound great compared to it's former self. Don't attempt this without the proper equipment.
-Chris
Thanks for the reply, anatech... I'm at work now so I don't have the chip numbers handy. Your procedure sounds OK, and the only equip I don't have is the distortion analyzer. I'll probably use my scope and my ears 😉 instead. I'd still like to find a schematic in case I find anything else wrong that isn't apparent yet, and I know I'll be the one called upon to fix any new problems.
sherlock
sherlock
Hi sherlock,
Well, a THD meter is pretty basic if you are working in audio much. Look on Ebay for HP 331A, 333A or 334A. A 339A is a wonderful thing or an 8903A (the only one I don't have).
The HP 331A are surprisingly good since they will measure you fundamental up to about 600 KHz (if memory serves). That means you get better answers than the Leader / Kenwood types that do not measure all the harmonics. A working one tends to go around $80 + / - $50. Try to get one with a manual.
With a THD analyzer, you can set bias current and actually see the crossover notch vary with your 'scope.
-Chris
Well, a THD meter is pretty basic if you are working in audio much. Look on Ebay for HP 331A, 333A or 334A. A 339A is a wonderful thing or an 8903A (the only one I don't have).
The HP 331A are surprisingly good since they will measure you fundamental up to about 600 KHz (if memory serves). That means you get better answers than the Leader / Kenwood types that do not measure all the harmonics. A working one tends to go around $80 + / - $50. Try to get one with a manual.
With a THD analyzer, you can set bias current and actually see the crossover notch vary with your 'scope.
-Chris
Hi Chris,
Actually, audio isn't my career, at least not anymore. I work as an engineer for a security company that makes the pedestals you see in stores that are used to prevent shoplifting. Once upon a time I had my own business and did all kinds of servicing, from simple radio, through CB and police and fire communications. As a result, I've got several pieces of equipment at home, some old and some new(er), that I use when something goes kaput, and I can borrow something from work if they have it and I need it. I also have a Ham license and a First-Class FCC Radiotelephone license. I normally just work on my own stuff anymore, but will help out a friend in need if asked. I usually try to stay away from doing alignments because they're a pain in the butt, but I'll drag out the sweep or multiplex generator if I have to. I've learned over the years that you save yourself a lot of grief if you follow the manufacturer's alignment directions as opposed to going it alone. If this were my receiver, I'd probably buy the service manual, just in case, but since this is basically a "free" repair, I don't really want to sink any money into it that isn't necessary, which is why I asked if anyone had a manual or schematic to share. Thanks again for your response.
Rich
Actually, audio isn't my career, at least not anymore. I work as an engineer for a security company that makes the pedestals you see in stores that are used to prevent shoplifting. Once upon a time I had my own business and did all kinds of servicing, from simple radio, through CB and police and fire communications. As a result, I've got several pieces of equipment at home, some old and some new(er), that I use when something goes kaput, and I can borrow something from work if they have it and I need it. I also have a Ham license and a First-Class FCC Radiotelephone license. I normally just work on my own stuff anymore, but will help out a friend in need if asked. I usually try to stay away from doing alignments because they're a pain in the butt, but I'll drag out the sweep or multiplex generator if I have to. I've learned over the years that you save yourself a lot of grief if you follow the manufacturer's alignment directions as opposed to going it alone. If this were my receiver, I'd probably buy the service manual, just in case, but since this is basically a "free" repair, I don't really want to sink any money into it that isn't necessary, which is why I asked if anyone had a manual or schematic to share. Thanks again for your response.
Rich
Hi Rich,
I fully understand your points of view. Did you get the number of the IC's in the FM or tuner section? Once you know what chip you are dealing with, the VCO alignment becomes very easy. It will probably confirm what I posted earlier.
The detector alignment I posted works most of the time. Exceptions are the more expensive tuners. Then you do need a manual.
On the THD meter, my point was that for playing around with your own stuff, a THD meter is wonderful. It unlocks all kinds of stuff you couldn't see before.
That piece of gear can become addictive.
-Chris 😉
I fully understand your points of view. Did you get the number of the IC's in the FM or tuner section? Once you know what chip you are dealing with, the VCO alignment becomes very easy. It will probably confirm what I posted earlier.
The detector alignment I posted works most of the time. Exceptions are the more expensive tuners. Then you do need a manual.
On the THD meter, my point was that for playing around with your own stuff, a THD meter is wonderful. It unlocks all kinds of stuff you couldn't see before.
That piece of gear can become addictive.
-Chris 😉
I haven't had a chance to get back to it. I'll most assuredly look up the chips before I do anything. I should be able to find the pinout on the internet. That's helpful, but it doesn't show the specific parts or testpoints on this receiver. I'll have to manage as best I can. At least the receiver can tune in stations and the stereo decoder works on some of them, even though I can tell it's not right.
I understand your reasoning about the THD meter. As I said, I try... to only work on my own things, and I do keep them in pretty good shape. In reality, I don't need more toys , I need more time! 🙂 🙂
Rich
I understand your reasoning about the THD meter. As I said, I try... to only work on my own things, and I do keep them in pretty good shape. In reality, I don't need more toys , I need more time! 🙂 🙂
Rich
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