Magnavox Astro Sonic 1968 - schematic & receiver bearings

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glark999
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Location: Tucson, AZ, USA

Magnavox Astro Sonic 1968 - schematic & receiver bearings

by glark999 » Sun Dec 27, 2015 8:56 pm

Hi Folks,
I am in the middle of repairing & refurbishing a 1968 astro sonic, chassis # R21203 BB (paper id tag) also id'd as R212 03-11 on the ink stamp. I have a few questions. If anybody can help, I'd be grateful.
1) Any tips on finding a schematic? Sams lists schematics for R21203AA and R2120300. Would these be similar/useable? The unit seems to have good volume and power, not too much noise, but as a precaution, I thought I would replace the capacitors. The nichicon caps are all legible for identifying the replacement values, but I would like to have a schematic just the same.
2) Help resolving a tuner issue: The tuner had good, smooth action for the first few weeks I used it, but then the dial got stuck in the 94-95 FM range while ascending the dial. I assumed it would be a bound up dial cord, but upon removal, I found the dial cord fine. Removing the dial cord entirely from the cord spool/condensor plates, I find the same bind-up/sticking issue always occurring about the same place in the rotation of the reciever shaft, and always in the direction ascending in frequency. I cleaned and re-lubricated the bearings at the top end of the shaft, and movement is improving (the dial cord is now able to pull through the rough spot), but it does seem like one of the ball bearings is out of line, or not spaced properly. Movement always gets difficult at the same location in the rotation, and I have to back up direction before dialing up again. Descending the dial, there is a similar problem, though not as pronounced. My question is this -- Does this sound like it could be a bearing issue? If so, is it worth/possible to fix? It doesn't seem that there is a way to replace the bearings without ruining the receiver, or at least its calibration... or ever getting it back together. No?
Thanks in advance,
Greg
Tucson, AZ

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MattTech
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Re: Magnavox Astro Sonic 1968 - schematic & receiver bearings

by MattTech » Mon Dec 28, 2015 12:43 am

R212's are R212's.
As for the defective/damaged tuning capacitor/bearing - replacement is the only way.
Then realignment per service manual.
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Rob-NYC
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Re: Magnavox Astro Sonic 1968 - schematic & receiver bearings

by Rob-NYC » Mon Dec 28, 2015 8:30 pm

Greg, the ball bearings in the tuning cap are obviously press-fit and not replaceable.

Check for a damaged section of teeth on the tuning cap gears and look for foreign matter in the ball race. I assume you looked for any chance that the pointer hits a wire or other slight obstruction.

Rob-NYC
"If we believe absurdities, we shall commit atrocities" -- Voltaire

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MattTech
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Location: Philadelphia Pa USA - Home Electronics - Service Technician

Re: Magnavox Astro Sonic 1968 - schematic & receiver bearings

by MattTech » Tue Dec 29, 2015 3:06 am

Rob-NYC wrote:Greg, the ball bearings in the tuning cap are obviously press-fit and not replaceable.

Check for a damaged section of teeth on the tuning cap gears and look for foreign matter in the ball race. I assume you looked for any chance that the pointer hits a wire or other slight obstruction.

Rob-NYC


Rob, those chassis use a direct drive tuning cap - no gears.
Some are binding due to manufacturing errors in the forming/bending process.
The Internet is a marvelous thing, however it's not a good substitute for actually being there.

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