Motorola 12K2 restoration

[Bill R]

Well I understand the space part, but if the CRT was good it might be worth a shot. After all it did survive an F4 tornado, 8 people did not. I think it wants to live. At least there is no intricate trim to reproduce on the cabinet. I will certianly be watching for pictures if you do restore it.

Originally Posted by bandersen

Luckily no critters were found - or droppings Just a lot of nesting material.
Yeah, I figured you guys would encourage me to save it. I'm willing, but it's got to go soon after I do. I'm way past out of space. The main challenge will be the cabinet. All the veneer has to be replaced

I'll start a dedicated thread once I begin work on it. I imagine this thread is getting confusing. For now, here's a quick look at the chassis.
Definitely cheaper that the TS-53. No bottom cover on the chassis and very little copper plating.

[Eric H]

I dragged my chassis home today, it does have the clear channel selector (somewhat yellowed or dirty) but I was wrong about it having the red knob with a squiggle, it's just a clear knob with a brass insert and it's busted to boot.

I still haven't looked to see what model it is.

[bandersen]

I have 2 or 3 spare red knobs, but they're missing the brass insert If anyone would like them, let me know.

I fabricated some new CRT mounts from a neoprene rubber sheet and glued them in place.



I recoated that 12LP4A with Aerodag and installed it. It's nice and bright
At first, I couldn't get the picture centered or focused well, then remembered that the entire focus assembly can slide back and forth. That got it



There are some light and dark bars. I'll try swapping the damper tube. Then get a test pattern going and tweak the linearity.

I was going to do an alignment, but I don't think there's any need.

[jeyurkon]

That's looking really good!

Is the raster shorter on the left than the right? Or that just the camera angle? When I had that problem it turned out to be the damping resistors in the yoke, and possibly the caps.

John

[bandersen]

Originally Posted by jeyurkon

That's looking really good!

Is the raster shorter on the left than the right? Or that just the camera angle? When I had that problem it turned out to be the damping resistors in the yoke, and possibly the caps.

John

Interesting - I hadn't noticed that. The camera may be at a bit of an angle, but not enough to account for the distortion I think.
The yoke in this set is a replacement and has 1200 ohm damping resistors rather than the more typical 560 called for on the schematic.

I'll know more once I get a test pattern hooked up.

Something else I just discovered. I was having a heck of a time polishing the bezel. It seemed like it was just clear coated brass so I try some stripper on it and it came away gold in some areas !

It seems that the inner surface is painted gold while the outer is clear coated. I wonder if that was to cut down on reflection and glare ?
I suppose I could attempt to reproduce the effect. I think it will be easier just to paint the whole thing gold though. Then it will match the trim I've already painted.

[TerrySmith]

If you scrap it out, it's gone forever! I'd poke it with a stick first to make sure nothing is alive in there.

Well after seeing your last video, I'd say maybe this one is too far gone! My previous comment was without knowing the condition of the cabinet.

Nice job on the 12K2! My wife even likes it!

I have noticed the "Zebra striping" as well in vintage TV's, possible interaction with the DTV converter box? Is it possible to shoot the composite audio and video directly in and bypass the RF and IF circuits?

[Electronic M]

Possible, but sometimes amp circuits must be built.

[bandersen]

I have this "zebra striping" problem Terry is referring to in addition to the keystoning jeyurkon noticed.
The yoke is a replacement and I wonder if it could be causing both problems

[kvflyer]

Originally Posted by bandersen

I have this "zebra striping" problem Terry is referring to in addition to the keystoning jeyurkon noticed.
The yoke is a replacement and I wonder if it could be causing both problems

Bob,

Keystone is almost always a yoke problem. But it may be a wrong value capacitor or resistor mounted in the yoke. Still, if you can find an original yoke, your problems may be solved...

[Komet]

Even my Panasonic CT-28 makes the zebra striping, I have to try replacing the damper tube or the EHT rectifier. Your set is very nice, I like it!

[Penthode]

My two cents...

I wonder if the zebra striping is the burst being displayed during horizontal retrace? A good test is to adjust the horizontal hold: if the zebra moves in the opposite direction to the picture when you adjust the control, that is it.

Remember that in the pre-color era, this would not have been a problem!

Otherwise, the stripes may be due to ringing on the forward sweep. Since it is on the left, the trouble would then be in the damper circuit.

Terry

I saw the pictures again and see the zebra across the screen. I bet it is the color burst on the screen.

[bandersen]

Interesting. I've had trouble with chroma dots on some sets, but not stripes.

Originally Posted by Komet

Even my Panasonic CT-28 makes the zebra striping, I have to try replacing the damper tube or the EHT rectifier. Your set is very nice, I like it!

Thanks! I looked through some vintage TV service manuals and they indicate the tripes could be caused by a defective damper, linearity control or yoke capacitor.

The yoke that came with this set was a replacement. It had 1,200 ohm damping resistors across the vertical windows and a 47pF cap across one of the horizontal windings.

However, this is what the schematic shows. Two 560 ohms resistors on the vertical windings. A 100K and a 2,700 in series with a 60pF on the horizontal.


So I rewired mine to match the schematic and swapped out the VOT. That just about got rid of the zebra stripes and keystoning. They are still faintly present, but not as bad as before.
I'll try tweaking the component values in the yoke a little.

[Penthode]

Hmmm. I find the problems discussed in this forum very interesting. I am suffering from a bad cold this weekend and the problems help keep my mind off my ailment. I trust you do not mind me discussing my thoughts and asking a couple more questions?

My synopsis: please jump in if you think this is not true. I suspect the resistors across the vertical coils, besides dampening the vertical retrace, would also dampen any ringing due to the horizontal retrace pulse ingress. The close proximity of the horizontal and vertical coils means that they will couple voltages. If the resistors across the vertical coils are too high, the horizontal retrace pulse could couple to the vertical coils, ring at a high frequency and the oscillating voltage couple back to the horizontal coils. This would then modulate the forward scan causing the ripples. This would imply that when adjusting the horizontal hold the ripples would remain stationary.

Putting the 560 ohm resistors in provided the necessary damping and should cure the ringing due to the above. And the keystoning would result from an imbalance on the yoke, so I suspect your rewiring and placing the matching resistors across half winding each solved that.

Could you confirm that when you adjust the horizontal hold, what happens to the ripple?

(Isn't the set's own CRT a terrific diagnosis tool?)

Terry

[jeyurkon]

That's what I had to do with my Sylvania replacement yoke, change the caps and resistors. The Merit catalog suggested making a box with a pot and cap to find the optimal values to substitute, but I found that the extra lead length made it useless.

John

[bandersen]

Terry, your theory makes sense to me. The ripples move in the same direction as the picture when I adjust the horizontal hold.

I can see why Merit made that suggestion. It sure is a pain swapping values with yoke mounted on the CRT neck.