Repairing a Motorola Cadet
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Hello all!
I've been a lurker for a while and this is my first post. I recently acquired a Motorola Cadet B&W portable, Chassis# D12TS-461A 01, that needs a little work. I've worked on old tube radios quite a bit (I have several of those), and tinkered with newer CRT monitors, but this is my first true effort in restoring an older TV. The symptoms are: Sound is clear with no hum. I get a bright full-screen picture with static on a blank channel, but I can't get it to sync on a channel with programming. Picture gets torn into 4 strips and interlace is poor, as you can see in these images: Attachment 195220 Attachment 195221 I bought the Sams for it, and things I've tried so far: -Swapped all the Horizontal and vertical tubes, even though the Motorola tubes installed in the set tested good (might be the originals!) -Replaced the two diodes in the AFC circuit. Unfortunately, neither of these actions solved the problem. Is anyone familiar with this set? Can you offer me any suggestions on what circuit or components I should look at next? Any advice is appreciated. I'm excited to get this working again! Thanks, Bill |
The Horizontal is running at the wrong frequency.
If it uses a coil with a slug for the horizontal hold control you may be able to turn it enough turns to bring it into range, if not then something in the horiz oscillator circuit has drifted out of spec. |
Thanks Eric. It does use a slug for the horizontal control, but the pictures I posted were as clear as I could get the picture to become after trying the entire adjustment range.
I'll start checking components in the horizontal oscillator circuit. |
Higher horizontal frequency, and if all tubes have been replaced, check the capacitors in the horizontal oscillator stage - particularly the one across the Horizontal Hold (Osc) coil - should be about .0022uFd to .0047uFd.
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Make sure that the slug in the coil form isn't stripped, so it doesn't move through the entire range of the coil. I've seen that happen. :thumbsdn: |
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Here's the schematic for his Horizontal Oscillator.
First check the slug is moving within L500. I was off a few uFds- the .0068uf (C507) swamping the coil, along with the .022uF (C508) would be my first swaps. If you have a scope, you can follow the horizontal sync and oscillator waveforms right down the line - just make sure either the scope or the TV is on an isolation transformer - the hot chassis is a problem. Doug Harmon posted about his TS-454 (same chassis electrically, laid out a bit differently) - his shows those putrid TRW burgundy caps that like to open. All the more reason I think you'll find a cap or two, possibly a resistor to be the culprit. BTW, the same Horizontal oscillator is used in the TS914 and possibly other Motorola Color Chassis: http://www.americanradiohistory.com/...-Page-0033.pdf |
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jr |
Fixed!
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I'm happy to report that the horizontal problem has been corrected! Dieseljeep's suggestion put me on the right track. The horizontal slug had gotten gummed up, and wasn't moving through the entire adjustment range. After cleaning it up and coaxing it past the sticky spot, I was able to get a good, clear picture!
Attachment 195264 Thanks to all who replied. This TV will be good for another 50 years now. -Bill |
I had one of these
It was my 30 min tv.... I bought it at a yard sale for $3 with a dim tube, added a brightener, sold it to my neighbor for $30.. :D SR |
[QUOTE=jr_tech;3187609]If it were really running too fast I think you would see stretched images... these are narrow and overlapped IMHO, the sweep is running too slow. :scratch2:
Thank You jr_tech , that is an interesting consideration , I didn't give a thought to the possibility of it being too slow . I now also wonder if the interlaced scanning also plays a part , could it possibly have been running at half speed to have been producing the 4 images ? |
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https://farm5.staticflickr.com/4430/...e03e79_z_d.jpg Could not get the set down to half speed, but i'm guessing we would see 2 non-overlapping images. :scratch2: jr |
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