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Old 03-07-2018, 09:49 PM
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Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 14,758
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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Tom C.

Zenith: The quality stays in EVEN after the name falls off!
What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
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