Motorola 21CT2B restoration

[Electronic M]

Originally Posted by oldtvman

When I had my shop sometimes I used to compare factory service manuals with photofacts. Sometimes they were right on and other times there were errors in the Sams version. I guess sometimes you had to take it for what it's worth, keep in mind a lot of time there were service bulletins that came out after both versions were released, and those had some very good info on them

I've had Sam's errors mess me up good enough on other sets to double check other literature when available.
I double checked the Sam's video IF alignment against the Motorola manual on the ETF and the video alignment was the same....
Rant time: both Motorola and Sam's (who appear to have copied Motorolas proceedure only renaming the coils to match their numbering) say to pull the horizontal output and to properly load the B+ to connect a 2K ohm 100W(!) Resistor across the B+...so I soldered 4 NOS 50s ohmite 500 ohm power resistors (with rheostat sliders not connected due to paper insulator) in series and set those in a jar...10min in I noticed the paper was smoking profusely so I pulled the plug about 10 seconds later the rigid assemblage of resistors desoldered themselves and collapsed to the bottom of the jar I was keeping them in for safety... Since I had more of those resistors I ended up using 16 in series-parallel to increase the wattage and make a 2K ohm resistor that needs an hour to char the paper... I have to wonder what Motorola was thinking specifying a 100W dummy load resistor...I don't think I have ever seen a TV that used a 100W resistor and I can't imagine the average repair shop would just have one laying around.

The video IF response on the first 2 injection points was dead on, the 3rd I was able to get close.

[Electronic M]

The third uses the tuner slug to get the 47.25 marker at %50 of the slope. The max it would go was in the %40-47 range. Bandwidth centering and flatness of the main curve were to spec... granted even with the tuner osc disabled the curve would change from channel to channel...most were an amplitude shift but a couple changed the shape...some showed the dip above the 47.25 trap and some didn't...

I finished the video IF alignment 2 nights ago. I think I did okay the picture and sound have not gotten worse (not much better either) and yesterday morning my by eye adjustment of the chroma osc would hold lock for about an hour if I let faces be a bit greenish and 10-30 min if I had the osc on the edge of it's lock where faces looked normal...

All and all I feel like I did well for my first attempt at doing a Video IF alignment on a TV.

[Electronic M]

Then in search of a stable chroma sync point where correct tint wasn't past the end of control travel I went and and messed up the chroma!

Last night I tried to do the chroma AFC adjustment procedure in Sam's and skip the chroma bandpass buuut Sam's instructs to touch up an adjustment from the bandpass so after starting the chroma AFC (which has totally detuned the osc, and possibly cracked a slug) I went back and started bandpass last night...the chroma bandpass proceedures first step was inject on pin 2 of the bandpass amp and went well, but the next step has me stuck. The injection point and circuit for the step I'm stuck on is nutty. They want me to build some goofy hand-wound ferrite transformer resistor isolation/matching network...I obviously don't have the Motorola core part specified on hand and I don't intend to look for it, but I did try to approximate the circuit....
I can get a signal from the generator through but it is so weak the markers on low are stupid wide and tall, there's a good bit of noise on the curve thanks to cranking up the scopes sensitivity, and the first 2 adjusters don't seem to affect the curve....

This Motorola is becoming a time vampire...I put a day into it and it barely improves...I just want to get this thing done, out of the basement and move on to other things...

[Tom9589]

Out of curiosity... What's the HV regulator on this set? A shunt regulator or a Victoreen regulator.

[Electronic M]

Originally Posted by Tom9589

Out of curiosity... What's the HV regulator on this set? A shunt regulator or a Victoreen regulator.

A normal 6BK4. This chassis was introduced in 1957 IIRC so it makes sense that Motorola would use the proven 6BK4.

[Electronic M]

I think I figured out the weird chroma bandpass curve...the half done AFC adjustment had detuned coils necessary to get the bandpass curve....I was able to reset 2 of the 3 slugs I adjusted for the AFC adjustment and get the chroma osc running off frequency and the bandpass amp curve suddenly existed and had some reasonable resemblance to what it should be... only problem is the 3rd AFC slug that cracked on me...I suspect the bandpass can't be done till the slug is fixed and the chroma osc is adjusted on (or atleast much closer to) frequency.