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Old 03-07-2018, 09:19 PM
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Electronic M Electronic M is offline
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Motorola 21CT2B restoration

Some time ago I made a deal on one of Motorola's rarest color TV models. After spending more than I paid for the set to ship it here from California (putting my total investment at the going rate for one of these sets) it arrived unscathed.



Radio63, the member here I bought this set from believes he may have purchased it from the original owners (CRT was already necked at the time) in the Fort Worth area. Which would make me the third owner, and make this the second early color originally from the region that I've purchased.

It arrived safely late Thursday the 24th. Over the course of that weekend, I managed to change nearly all the capacitors. I decided not to restuff the paper caps since most were tubular ceramics. Even if I restuffed other paper shells it would not look right, plus the chassis was a bit cramped around some caps. Most of the peaking coils were defective too. I've replaced most with close approximations, but need to order better ones for some places (that will be on my next bulk parts order).



More chassis pics can be found here: https://www.flickr.com/photos/137849...h/40425548112/
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Old 03-07-2018, 09:49 PM
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I decided to replace the 21AXP22 CRT with a 21FJP22 I had until I can source a 21AXP22 (I could really use a couple of those)...I've done this procedure before on a CTC-4. The Motorola proved both easier and harder than a 4 in its own ways. I was able to get the stock mounts to just barely reach and hold the FBP in, but the yoke mount that is part of the CRT mounts was too high relative to the neck for the yoke to mount properly...So I had to get creative. I struck out on junk box hardware for the mod, and the right size of threaded rod to replace the top ones was not stocked so I came up with extenders made from coupling nuts an eyelet and a hook. I had to Dremel down the shafts, but they worked. I also notched some rubber grommets to use as ~1/4" spacers between the grounded yoke mount and the HV suction cup....In the process of doing that the Dremel managed to catch the rubber and ride it up on to the thumbnail holding it. It went clean through the nail and into the flesh enough for it to eventually bleed some (burned it shut partially as it cut/ground) and scare the sud outa me. I did get the mount done though. The nice part was that instead of molding the HV wire into the plastic shroud Moto routed it under the shroud and to a metal clip. I was able to unsolder and save the clip and add a suction cup to the end of the HV lead which saves me from having to jury-rig a plug for the HV lead connector like on my CTC-4. I can reverse this CRT swap and go back to a 21AXP22 with the original unmodified hardware anytime almost as fast as one could change a CRT in this model.

//Todo Tom: quit stareing at yer thumb and take a picture of the new crt in it's mounts!

Hot was weak, so I swapped it. I gave it a powerup on the bench and got good H drive so I gave it a power-up in the cabinet. First try heaters light, but otherwise dead (learned of power rect. socket/wiring intermittents). Second try sound with horizontal lines video modulation in lines, screechy Horizontal whine, and occasional pops accompanied by brief vertical stage operation. Third try raster...Horizontal adjusted for sync (which stopped the screech) vertical running at 120Hz shrunken/non-linear intelligible video...This is about where I stopped yesterday. I went over the vert stage resistors. Some were changed to values not in the Motorola issues schematic on the ETF...Others appeared original but different value. Getting resistors in tolerance did not fix vertical issues. I wish I had a copy of sam's 371 for this set to cross-reference.
The occasional loud pops seem to be arcing from one of the screen pots...It only did it once for me on the bench.



I'm probably going try decade box engineering the vertical RC time constants soon if making it match Moto's service lit don't fix it.

There are plenty of interesting observations about the construction, design, and repair work I'd like to make, but it is getting late, so I'll make them another day.
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Old 03-09-2018, 06:23 PM
dieseljeep dieseljeep is offline
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When doing a job like that, always have a tube of Super Glue handy!
It was originally intended for that. For minor injuries, I use it all the time.
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Old 03-09-2018, 07:18 PM
Tom9589 Tom9589 is offline
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My wife is from Kingsport, TN, home of Tennessee Eastman. Eastman came out with one of the first cyanoacrylate glues, called Eastman 910, in the late 60s. It was pulled from the market when they discovered that doctors were using it to "glue" incisions on people. I managed to snag a tube and it was absolutely amazing at gluing things back together. No, I didn't use it on any wounds, but 30 years later a similar product was used on some major surgery I had. Worked great.
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Old 03-10-2018, 10:16 AM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by Tom9589 View Post
My wife is from Kingsport, TN, home of Tennessee Eastman. Eastman came out with one of the first cyanoacrylate glues, called Eastman 910, in the late 60s. It was pulled from the market when they discovered that doctors were using it to "glue" incisions on people. I managed to snag a tube and it was absolutely amazing at gluing things back together. No, I didn't use it on any wounds, but 30 years later a similar product was used on some major surgery I had. Worked great.
I had read or understood that the product was developed as a temporary means of mending injuries in battle during the Vietnam War.
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Old 03-11-2018, 10:42 PM
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Tom, I'm very happy to see the progress you've made on this set! After so many years of being dormant, it's great to see it lit up and slowly coming back to life. Will be following along as you move forward.
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Old 03-12-2018, 11:41 PM
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Good to see this thread got back on the original topic.
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Old 03-13-2018, 10:37 AM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by reeferman View Post
Good to see this thread got back on the original topic.
I tried to enter a new, more relevant entry to this topic regarding the tricky color circuit used in the Motorola set, but my new playfull kitten jumped on the keyboard and erased it.
I didn't know it didn't get entered.
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Old 03-15-2018, 11:27 AM
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Quote:
Originally Posted by reeferman View Post
Good to see this thread got back on the original topic.
It does make one worry about VK when a resto topic for an early color set that only 9 examples of are known to remain goes straight into a discussion of stupor glue... I've never had good luck gluing my wounds, so I save the stuff for certain resto tasks such as fixing the occasional terminal strip wafer snapping in two.

I was able to make all the vertical stage resistors match the schematic from the ETF. http://www.earlytelevision.org/pdf/m...905_manual.pdf
Several were marked different values from the schematic, and some of the different ones were clearly replacements that were tacked in ages ago. Changing the resistors did not solve or change the problem...Scoping revealed it is closer to running at 3X correct frequency than the 2X I assumed earlier.
I could not find my RC decade box, but jumping capacitors and resistors in did not help/change much.
Voltage checks indicate there are major issues in the output...The grid of V15 should be -14V to -2.8 it seems to only be adjustable from -3V to 0V...The plate voltage is low and the cathode is high indicating excessive current flow in the output tube (big shocker given the grid voltage lol). The linearity control seems to be ineffective.
I really wish I had sam's 371 right now...I've got every sam's folder from 101-580 EXCEPT for 371 (which contains the folder for this set)...Just my luck. I'd really like to cross reference the sam's lit.

Presently I'm stalled on this project...Not by the set but by the flu. I've been running 102 fevers on and off all week and have been feeling generally miserable. No basement bench time for me for now.
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Old 03-15-2018, 07:40 PM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by Electronic M View Post
It does make one worry about VK when a resto topic for an early color set that only 9 examples of are known to remain goes straight into a discussion of stupor glue... I've never had good luck gluing my wounds, so I save the stuff for certain resto tasks such as fixing the occasional terminal strip wafer snapping in two.

I was able to make all the vertical stage resistors match the schematic from the ETF. http://www.earlytelevision.org/pdf/m...905_manual.pdf
Several were marked different values from the schematic, and some of the different ones were clearly replacements that were tacked in ages ago. Changing the resistors did not solve or change the problem...Scoping revealed it is closer to running at 3X correct frequency than the 2X I assumed earlier.
I could not find my RC decade box, but jumping capacitors and resistors in did not help/change much.
Voltage checks indicate there are major issues in the output...The grid of V15 should be -14V to -2.8 it seems to only be adjustable from -3V to 0V...The plate voltage is low and the cathode is high indicating excessive current flow in the output tube (big shocker given the grid voltage lol). The linearity control seems to be ineffective.
I really wish I had sam's 371 right now...I've got every sam's folder from 101-580 EXCEPT for 371 (which contains the folder for this set)...Just my luck. I'd really like to cross reference the sam's lit.

Presently I'm stalled on this project...Not by the set but by the flu. I've been running 102 fevers on and off all week and have been feeling generally miserable. No basement bench time for me for now.
That was the wrong poster to pay attention to.
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  #11  
Old 03-24-2018, 10:31 PM
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Some progress; I got the vertical working right. The 4700pF cap on the vert osc trans had drifted in value a good bit...However, the real issue appears to be tin whiskers in the hold pot. I was briefly able to get the freq right while rotating the control, hitting it with cleaner while running and working the pot cleared the whisker.



Thanks to referman for supplying the sam's. I was able to confirm from cross-reference that one of the 'wrong value replacement' resistors were correct value in the sam's revision.

I was able to get off freq chroma osc noise in the video so the chroma section has life...I need to check the chroma stage tubes. This set has an interesting chroma section...It has the diode demodulator circuit of a porta-color, but with a crystal chroma reference osc like most other sets.
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What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

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Old 03-25-2018, 01:13 AM
EdKozk2 EdKozk2 is offline
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It's looking good Tom.
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Old 03-25-2018, 03:32 PM
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Nice progress!
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Old 03-26-2018, 01:04 PM
kvflyer kvflyer is offline
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Tin Whiskers... Hmmm, I have an Admiral 26R12 that I restored. It was working well on the bench and then all of a sudden, I heard a snap and lost vertical linearity. It took a long time to figure out (didn't check the obvious) that the vertical linearity pot had tin whiskers. I removed the pot, cleaned and brushed it and all was good. What a relief that was!

Nice job.
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Old 03-26-2018, 03:25 PM
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