Motorola 19K1 restoration

[bandersen]

I've finally got some signs of life out of this beast. I had hooked up one end of this coupling capacitor wrong. That was preventing the final video amp stage, sync circuits and audio amp from getting a signal.


Here's the output from the 6AS5 cathode follower final video amp stage.


Output from 6V6 audio amp.


The horizontal drive signal at the 6CD6G HOT looks OK. Still no picture though and the HV is a bit low. I'm going to check the damper tube, flyback and doorknob capacitor.


The vertical oscilliator is running at 84 Hz and the amplitude is half of what it should be. I need to so some more checking there too.

[Eric H]

Since your HV is low you might try it with a 10 or 12" tube and see what happens.

Is that voltage taken without the CRT installed or with? Perhaps the metal cone is leaking to ground somewhere.

[bandersen]

I'm getting about 9KV with the little 5AXP4. I figure I should be getting some sort of image. I'll check the voltages on the CRT cathode and grids.

[Eric H]

Doh! I thought you were using the 19" tube for some reason.

I have another dumb suggestion, is the heater lit on the test tube?

I've chased my tail a few times looking for something else only to find i had a dirty CRT socket.

[leadlike]

Could the doorknob cap be leaking HV, shunting it to ground? I once had a tv with low HV, it turns out the chassis was leaking HV to a metal rail that was part of the table it was sitting on! I measured about 9kv on the lead, and the table rail read about 1 kv.

Another possibility to explore-is that the proper flyback in the set? With all the hacked repairs someone was doing on the hv section, they may have been trying to put in a different flyback (hence the single doorknob cap-like they were trying to emulate the circuit the replacement fly came from?)

[bandersen]

Originally Posted by Eric H

Doh! I thought you were using the 19" tube for some reason.

I have another dumb suggestion, is the heater lit on the test tube?

I've chased my tail a few times looking for something else only to find i had a dirty CRT socket.

Yeah, it is - I wish it was that simple

Originally Posted by leadlike

Could the doorknob cap be leaking HV, shunting it to ground? I once had a tv with low HV, it turns out the chassis was leaking HV to a metal rail that was part of the table it was sitting on! I measured about 9kv on the lead, and the table rail read about 1 kv.

Another possibility to explore-is that the proper flyback in the set? With all the hacked repairs someone was doing on the hv section, they may have been trying to put in a different flyback (hence the single doorknob cap-like they were trying to emulate the circuit the replacement fly came from?)

Good call. I hadn't checked that before. It's a Thordarson FLY-40 which is actually the correct replacement for the original Motorola #24C792691.

I'll fire up my EICO 944 flyback & yoke tester and check it out. Might as well check the yoke too while I'm at it.


Here's another look at the darkened area Eric noticed earlier. It looks like there may have been some arcing in the past.


I think I can pull some doorknob caps out of my Admiral 19A15S. Someone replaced the old 6KV paper caps with several of them I've been meaning to replace them with some nice ASC plastic HV caps. Might as well do it now.

[bandersen]

Well, I tested the flyback, yoke plus all the coils and transformers. They all check out OK, except for one tap on the flyback. It should be about 0.8 ohms and I'm getting around 12 which seems odd. I'd expect a bad winding to be either open or have a lower reading if there are any shorts. The EICO indicates that the fly is good though. Maybe the FLY-40 is a little different than the original Motorola ?

I also swapped out the doorknob cap. I fired the set back up and still only had 9 kv. I gave the horizontal lock a few clockwise turns and was able to get it up to 12 kv, but horrible high pitched squeals were coming from the flyback so I backed off. Still no image at all. I checked the voltages at the CRT pins - they're fine.

Before I called it a night I swapped out the 5AXP4 for an 8XP4 just for the heck of it. At last, a faint glimmer of life


I had to crank the focus control all the way which got me thinking maybe the focus coil could be having a bigger effect than I expected. These little test CRTs are auto-focus so don't need one anyway. I physically moved the focus coil around and got a much brighter trace!


Just to make sure the 5AXP4 is OK, I put it back in. I never figured a focus coil position could have that much of an effect! (Yeah, I know that's not the safest HV anode lead )


Which leaves me with a nice bright trace with no horizontal at all. The width control barely has any effect.
So how is it possible for the flyback to put out HV when there's no horizontal deflection There is a mica cap inside on the horizontal winding inside the yoke. I'll check that tomorrow.

[bandersen]

I finally found the problem - a bad horizontal yoke connection. The HV is up to about 14 kv now.

Here are the first images I got using the rectangular 8XP4. First, using a B&K 1077B which is in need of an overhaul. Next, a low power analog broadcast picked up with rabbit ears.


I'm getting some weird clipping so I switched back to the round 5AXP4 and did some tweaking.


Almost every control is crammed into one corner. It's convenient, but a little tough when you have big hands.


Next, I fired up a Leader test pattern generator. The RF output on it is too weak to produce a decent picture so I fed it into a BT modulator. It's not just his set - the Leader RF is just too weak for any set I've tried it on.

Here are the alignment, convergence and multi-burst patterns. I'll hold off on making an more adjustments until the 19AP4 has been installed.


Finally, I hooked up a DTV convertor box. No sound, but I was expecting that. I have a couple of these Access HD DTA1010 boxes and get very weak or no sound on most of my vintage sets. One solution I've used is to feed the composite output from the converter into a BT modulator.


I'm going to clean up some temporary repairs and clear off the workbench before remounting that 19AP4.

[Boobtubeman]

Its alive..... ITS ALLIIIIIIIIiiiive!!!

[Eric H]

Holy short circuit Batman, it's working!!!

[zenithfan1]

Great job Bob! This one looked like a real challenge that turned out to be totally worth the effort I can't wait to see it back in the cabinet and done!

[bandersen]

Originally Posted by Boobtubeman

Its alive..... ITS ALLIIIIIIIIiiiive!!!

Muwahahahaha....

Originally Posted by Eric H

Holy short circuit Batman, it's working!!!

Short circuit indeed between the horizontal winding and focus coil.

Originally Posted by zenithfan1

Great job Bob! This one looked like a real challenge that turned out to be totally worth the effort I can't wait to see it back in the cabinet and done!

Thansk! Me too. I'm still not sure how that's going to happen though. I think the cabinet is still somewhere in Illinois. I just have the chassis and picture tube. Somehow they need to be brought together and reassembled at the sets owner's (Nixer) place in Tennessee

[Eric H]

As I recall the cabinet was pretty beat up, is it being repaired too?

[bandersen]

Originally Posted by Eric H

As I recall the cabinet was pretty beat up, is it being repaired too?

Yes, last I heard.

"I’ve actually talked to Sandy about Jim Obermeyer before and I’ll definitely be taking the cabinet there."

I'm really curious to see what a pro can do with it. I'm guessing the top needs to be re-veneered ? Just about everything in that darn antique shop it came from had some cabinet damage.

[jeyurkon]

That was pretty fast detective work!

I have an Access also and it produces weak sound and awful picture via RF even on modern sets. Works great with a BT though.

That horizontal something coil looks like a real pain to adjust.

I'm anxiously awaiting to hear how the professional refinishing goes.

John