View Full Version : Repairing a Motorola Cadet


Billreed79
08-02-2017, 07:38 PM
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:
195220
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

Eric H
08-02-2017, 09:26 PM
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.

Billreed79
08-03-2017, 06:51 AM
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.

Findm-Keepm
08-03-2017, 10:39 AM
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.

dieseljeep
08-03-2017, 12:34 PM
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.
I haven't seen a set exhibit that problem in probably 40 years. :sigh:
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:

Kamakiri
08-03-2017, 05:23 PM
I haven't seen a set exhibit that problem in probably 40 years. :sigh:

Common when restoring a set like a 630TS or even an RCA roundie. Synchro guide circuits do that when they're out of whack. Every time I restore a 630 chassis set, power it up.....4 images, turn the synchro guide, 3 images, keep turning, 2, BINGO!

init4fun
08-03-2017, 11:23 PM
Common when restoring a set like a 630TS or even an RCA roundie. Synchro guide circuits do that when they're out of whack. Every time I restore a 630 chassis set, power it up.....4 images, turn the synchro guide, 3 images, keep turning, 2, BINGO!

The first time I saw the 4 image synchro guide misadjustment trouble it made me wonder , the horizontal , which runs at 15 KHZ (15750 to be exact , yes ?) , could it really be running 4 times too fast , at some 60 odd KHZ (63000 ?) from a circuit optimized for 15 (ish) KHZ ?

Findm-Keepm
08-04-2017, 01:16 AM
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/hd2/IDX-Service-&-Sales-IDX/Archive-Radio-Retailing-IDX/IDX/60s/Electronic-Technician-1965-10-OCR-Page-0033.pdf

dieseljeep
08-04-2017, 11:09 AM
Common when restoring a set like a 630TS or even an RCA roundie. Synchro guide circuits do that when they're out of whack. Every time I restore a 630 chassis set, power it up.....4 images, turn the synchro guide, 3 images, keep turning, 2, BINGO!

I just repaired an RCA Synchroguide circuit a few months age and it wasn't off that far. The set wasn't as old as the 630, but the circuit remained pretty much the same from the very begining! :scratch2:

jr_tech
08-04-2017, 01:05 PM
The first time I saw the 4 image synchro guide misadjustment trouble it made me wonder , the horizontal , which runs at 15 KHZ (15750 to be exact , yes ?) , could it really be running 4 times too fast , at some 60 odd KHZ (63000 ?) from a circuit optimized for 15 (ish) KHZ ?

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:

jr

Billreed79
08-04-2017, 05:00 PM
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!

195264

Thanks to all who replied. This TV will be good for another 50 years now.

-Bill

Boobtubeman
08-04-2017, 06:30 PM
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

init4fun
08-04-2017, 08:20 PM
[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 ?

init4fun
08-04-2017, 08:21 PM
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!

195264

Thanks to all who replied. This TV will be good for another 50 years now.

-Bill

:D Gotta love a success story !

jr_tech
08-06-2017, 04:26 PM
[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 ?

Here are 4 overlapping images on my 7" Airline suitcase TV which is being re-capped. Horiz frequency is about 12.6 to 12.8 kHz.

https://farm5.staticflickr.com/4430/36014310930_b50ce03e79_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

Findm-Keepm
08-06-2017, 07:59 PM
[QUOTE=init4fun;3187626]

Here are 4 overlapping images on my 7" Airline suitcase TV which is being re-capped. Horiz frequency is about 12.6 to 12.8 kHz.

https://farm5.staticflickr.com/4430/36014310930_b50ce03e79_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

...and usually the flyback is singing :sing: a tune as well. I can no longer hear frequencies that high, and when the Emerson I worked on a year ago drove my daughter bats......Clue! Horizontal is running too slow....two caps and tube later, and she was well again. Sadly, the tuner has failed mechanically - the plastic holding the tuner strips in has dry cracked - I've got her stuck on channel 4 for now.