More Motorola Horizontal blues :(

[nasadowsk]

Ok, I've got the HV up, the set works, there's sweep, BUT:

I've a nasty bar to the left of the drive line. It looks like a 2nd drive line, almost.

The flyback's a Thordarson Fly-40, the Yoke's a Merrit MDF-70.

Attached is the schematic. The set's currently in the factory-built configuration, but there were changes to it as found:

1) There was an additional 250 pf cap bridging the drive adjustment (green area)
2) The size control was disconnected (red area)
3) The .03 cap was to the 290V supply. Physically, installed across the terminals on the flyback.

#3 doesn't seem to affect anything, though having it out of the circuit maked things worse (lots of drive line-like bars)

I disconnected the size control, this fixed the bar issue, but blew the width up a LOT.

Adding back the 250pf cap brought the size down, got rid of the drive line, but cost brightness.

Now, the question is, do I leave it this way, or was this a 'quick fix' for something else, and if so, where do I look? The flyback's sheet says it's a replacement for _only_ this set's flyback, but the yoke isn't exact. I've put the right cap in the yoke, but not much change (unless the cap I robbed out of the old yoke was bad?).

I know most later sets didn't have width adjustments, but I'd like to have that work here if I could, and frankly, unless there's something I'm missing, here, I don't get why the factory setup shouldn't work..

Anyway, here's a link to the horizontal section - I chopped the schematic to get rid of (seemingly) unrelated stuff and make it fit in a window...

Oh yeah, the damper's been changed - no dice. The old output had a magnet tied to it - but this just doesn't look like snivets...

As an aside, I STILL can't get this thing to focus right, I'm not sure why, but I don't think that's related anyway - the HV's pretty much in spec, though it does drop at the high brightness setting...

http://farm4.static.flickr.com/3107/...c514e4eb_o.jpg

[Reece]

Worth trying the magnet on the output tube again and moving it around to see if you get rid of some of the problem.

Reece

[nasadowsk]

I thought that too, but it seems like a bad fix for something else.

I *did* measure the DC resistance of the width coil, it's about 1/2 of what it should be, at least according to the Sams. That doesn't make any sense, though. (a 1/2 short?)

On the flip side, the biggest effector of things is connecting/disconnecting the width coil. If I had an idea what the inductance should be, I'd get a few in the range and swap them in/out and see if that did anything. Maybe it *is* a bad coil?

[Old1625]

A pic of exactly what is happening on the screen would be helpful here...

Seems that the width coil needs to be more closely examined. Any number of shorted turns in that coil could create all kinds of interesting loading effects on the system, resulting in varied results.

I dare say that a comparison of the waveform that should be in that horizontal sweep circuit as compared to what you are currently getting there may prove interesting.

[nasadowsk]

I don't have a camera handy (I could try to, uh, borrow, my parent's ), but I can scope waveforms at any rationale point (i.e., not the horz output plate!). The drive looks pretty much correct, and is the right size.

I'm starting to really think long and hard about that width control. The resistance doesn't match the book value, and hooking/unhooking it is the big effect on the picture...

[premiumplus]

Are all your electrolytics up to par? I've seen 10uF caps do that to horizontal...

[nasadowsk]

Hmmm. I don't know. It's interesting, though - with the width control gone from the circuit, and a 250-pf cap in the drive, the picture's missing all vertical drive lines, etc. It's a slight bit off size.

The width control according to Sams is 50 ohms DC resistance. I'm getting in the 20's.

I wish I knew what inductance range it was, I'd get a few fixed inductors in the range and swap them in and out and see what happens. At one time, this set wasted a flyback and yoke - I'm starting to think the width control was a victim, too.

I don't know where I'd find another one, I guess it could be rewound, but I don't have the winding equipment to do it

The other outstanding issue is I can't get the set to focus right - the focus control either has little/no effect, or in other places just shifts the raster slightly. I can juggle the ion trap magnet around, and that affects focus, too.

Does anyone know how the magnet and all on a 19AP4 is supposed to be set up? I have just one magnet, but I know nothing about these weird bent gun type tubes...

[Don Lindsly]

The ion trap should line up with the magnet over the socket pins. If not, put the open end over the pins and fine adjust for max brightness. If the tube calls for a double magnet ion trap, it may not focus with a single. If it is a rebuilt CRT, it probably uses a single in any case.

You may never get the horizontal perfect with a Merit yoke. Motorolas of that vintage went through a lot of yokes and seem to need an original to work properly. Merit is always the last choice in generic replacement parts; absolutely the worst.

[nasadowsk]

Hmm, I still can't get it to focus right

Removing the yoke and focus coil, I found the ion trap had the following effects:

1) Rotating it moved the spot left and right.
2) Sliding it forward moved it up and down.

Not exactly, but on a slight angle. The spot was bounded by a circle - the cutoff happens when you go outside it.

Without the focus coil, it's a round spot, very large even when dim.

With the coil, it's not a spot but an ovalish line.

I can't tell if the focus coil isn't strong enough, or isn't far forward enough, or what. The focus control has minimal effect on the spot, though the coil's resistance checks out.

ugh

[nasadowsk]

Ah ha!

I pulled the focus coil wires off the set and grabbed my trusty Heathkit HV supply...

1) With the wires one way (red + blue -), the coil worked as advertised, and focused a nice bright raster. Well, almost bright enough - it doesn't bloom but there's scan lines at full brightness....

2) Reverse the wires, uh oh - no go.

This makes sense - it's a coil+magnet type focus. If it's 'bucking' the magnet, it's gonna need a lot more ommph to focus. The ommph I measured in the right direction was about 75-100v, into the coil's 1400 ohm resistance. The wrong way, it needs wll over 100v to get even close, and it works like crap anyway.

Checked the schematic. Whoops.

Hooked the wires up the right way - hey neat, you can actually watch this thing now!

With the focus coil's wires flipped and some minor adjusting, I had the best pictures I've had yet on this set. Not amazing, but respectable - almost watchable. There's some gremlins to chase down still, though:

1) Retrace lines - I get these no matter what. Looks like someone's not being a team player in the CRT area.

2) The flyback gets warm. Not hot, but warm.

3) I'm starting to really think that size coil's bad - it was disconnected when I got the set, which had it's OEM yoke (blown). Looked like it was that way a long time, too.

4) Sound has vert buzz. Minor touchup, I think.

5) Larry The Cable Guy isn't very funny at 1:30am.

Question - given that this is a 'bent gun' CRT, does the rotation of the tube vs the focus coil affect anything? I installed the CRT more or less random, but am wondering if turning it a bit would allow me to tighten up the focus, which is pretty good but not what I expected - I can't get a perfect dot, more like a tiny blob.

[Tony V]

To check that the crt is in the right position...looking at it from the rear, the anode button should be at the 3-o'clock position. You can try rotating it a little one way or another but dont think it will make alot of difference. I know some of the guys who have had focus problems in the past on sets with a focus coil usually were able to get a little more sharpness out of them by playing with the voltage going to coil. I assume the crt has good emission as its critical on these type sets because if its just marginal it wont haver razor sharp focus. I would also try to locate a proper size coil for this set also as all of it has a hand in proper HV and sharpness along with scan.
-Tony

[nasadowsk]

Originally Posted by Tony V

To check that the crt is in the right position...looking at it from the rear, the anode button should be at the 3-o'clock position. You can try rotating it a little one way or another but dont think it will make alot of difference. I know some of the guys who have had focus problems in the past on sets with a focus coil usually were able to get a little more sharpness out of them by playing with the voltage going to coil. I assume the crt has good emission as its critical on these type sets because if its just marginal it wont haver razor sharp focus. I would also try to locate a proper size coil for this set also as all of it has a hand in proper HV and sharpness along with scan.
-Tony

Ahh, it's a 19AP4 - metal tube. No CRT button

It's brand new, maybe 2 hours on it.

I'm gonna look at the focus divider, etc. It's not bad, it's just not what I expected, and frankly, it might be right anyway.

That width coil, that's the bigger issue. Heh. I'm not sure where I'd find one - it's Motorola part # 24K792722. No idea what inductance range, just DC resistance of 50 ohms. The coil winding is about 1 inch wide, 3 turns per layer, no idea how many layers. I guess it could be rewound, somehow...

[jeyurkon]

Originally Posted by nasadowsk

Ahh, it's a 19AP4 - metal tube. No CRT button

It's brand new, maybe 2 hours on it.

I'm gonna look at the focus divider, etc. It's not bad, it's just not what I expected, and frankly, it might be right anyway.

That width coil, that's the bigger issue. Heh. I'm not sure where I'd find one - it's Motorola part # 24K792722. No idea what inductance range, just DC resistance of 50 ohms. The coil winding is about 1 inch wide, 3 turns per layer, no idea how many layers. I guess it could be rewound, somehow...

I don't know if this would be of any help. I could check it with my LC101 impedance analyzer. It has a ringing check that makes a basic measurement of the Q of a coil. That would probably show if it has a short. If your DC resistance measurements and the Sams are correct, then that sounds like it might be the case.

If you want to mail it to me send me a PM and I'll give you my address.

John

[nasadowsk]

Lemme think about that. Right now, the TV's off the bench for a bench clean and to get the radio 1/2 of the set rolling.

At least knowing the coil's bad helps, then I can start hunting for a replacement or rewind this one or whatnot...

At some point, I wanna chase down a flyback for my Magnavox, too. That's a Stancor A-8117. or Chicago TFB-1. the HV winding's toast in mine, which blows cause the set works decently enough otherwise...

[nasadowsk]

Ok, I called Moyers, they've got a coil in stock, and yeah, their's was 50 ohms, which the cut sheet says it should be, too.

So, I've got a bad coil :/

I think that should get the last Horizontal gremlins out, and then things should be kickass with the sweep on this set...