Author Topic: Astrosonic R214 Re-cap, then discovered Channel Two is dead...  (Read 12993 times)

ed from Baltimore

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Re: Astrosonic R214 Re-cap, then discovered Channel Two is dead...
« Reply #30 on: July 24, 2019, 07:46:46 AM »
     I see now it was no stereo  light, but do you have any tuning meter on FM.??   
             Without -34 volts on the collectors of Q 14 and Q 19, I don't think you would get any decent audio, even out of one channel. If you have decent audio on at least one channel (I assume an FM station ?) you should have -34 volts or at least more than 0. 
             BTW,  if you have an analog Simpson type voltmeter and you are expecting + 34 volts and have your leads arranged that way, you may not notice the meter moving slightly below 0 as it pins to the left and assume it's 0. Speaking for myself, I am constantly goofing up when measuring negative polarity transistorized circuits cuz I'm so used to tube positive polarity stuff.
         So,-- assuming you have fixed the -34 volt problem, I am wondering--are you forced to tune in the FM stations by ear because you also have no  tuning meter peak ? I know that on my similar Magnavox chassis, you have to do three things to get the stereo lamp to light.    First  on  FM,  peak the tuning meter on a really strong FM station with a high peak. Then, turn the selector switch to FM-AFC  and make sure the peak doesn't shift away lower. It should stay high up.   Then finally, turn the switch to FM STEREO. The tuning peak should stay high. The stereo lamp should light and the background hiss should get a 3D sound to it, but this you might not notice unless both channels are working evenly.
        If you can't get a good peak on the tuning meter, the stereo lamp will usually not light. A shorted C7 (goes to the tuning meter) or a shorted or open X5, inside the AM IF can, will get you no AM and make it impossible to peak the tuning meter on FM which will get you no STEREO indicator lamp. Hopefully fixing one will fix the other.
       I know it's a lot to digest, and I had to write it out without proofreading cuz I am checking out of the motel for now, but I know you, the voltmeter, the scope, and the schematic will fix it all up. Then all that's left is the one weak / distorted channel ??  Good luck
       

Phillip Colwart

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Re: Astrosonic R214 Re-cap, then discovered Channel Two is dead...
« Reply #31 on: July 24, 2019, 07:14:06 PM »
Dave,

RE: Reply #27

Yes - changed all electrolytics and all resistors but one on the drive board, as well as two transistors (the other four tested okay).  I also replaced the two speaker coupler electrolytics and two other electrolytics and a couple of "suspicious looking" resistors along the point-to-point wiring in the amp section.

Ed, Reply #28

Waiting with bated (smells like fishing bait) breath.  Am doesn't work but to clarify, the tuning meter does work on FM.  The FM Stereo indicator does not work, and I believe the 1kΩ trimmer pot is the culprit.

Ed, Reply #30

Okay, this is great stuff!  Yes, the tuning meter does not go fully to 100% on a loud, local FM station.  And yes, C7 is funky.  That is, the plastic sleeve on the aluminum can has pushed itself upward.  I was fearful of replacing C7 and C5 because of their proximity to that can, going on the thought that replacing caps in the radio section could require receiver realignment.

So, I will add two 50uF 25 volt electrolytics and that 1kΩ trimmer (full size) to my next parts order. This may square away the radio section, and I will address all the previously mentioned things to fully restore channel 2 audio.  The Selector switch sounds clean but I will Deoxit again and do some audio signal tracing, etc.

I've pasted all relevant comments to a word document so I can chase each point and stay on track.

Had to stop work on the R214 to earn some money (I'm self-employed), and might find time next week to get back on it.

Still reading for hints and tips, will report back!

Thank you!


Astrogoth

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Re: Astrosonic R214 Re-cap, then discovered Channel Two is dead...
« Reply #32 on: August 03, 2019, 01:24:45 PM »
My R214 has the same dim STEREO lamp as yours. I think yours is working perfectly. My tuner bulbs are far too weak to see so I replaced them with green LEDs and backed them with two strips of foil to act like reflectors. Now I can read the frequency at night!
Astro Sonic, Model 30, Early 1968, #1P3702, Chassis R21404 French Provincial, Cherry.