Predicta Holiday - First power up attempt

[Phil Nelson]

Originally Posted by madlabs

Once I get the vert. lin. straightened out

Have you ever looked at the centering widgets on the yoke? There's a diagram in Sams that points to them. On one of my Predictas, the centering was way off, making it harder to get correct linearity. The misadjustment might have been the result of a past repairman trying to compensate for an aging component. Can't hurt to check, anyhow.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[Electronic M]

I generally put up a crosshatch pattern and jump between the Height, lin and centering till I have a reasonably linear centered-ish picture. Compromise and incremental improvement can be the name of the game if it don't just fall into adjustment.

If the tube is good, generally resistors and caps are next, a check of the B+ and b+ Boost rail voltages feeding the circuit, and last the transformer and yoke.

For HV wire on normal sets I just find a big-screen 90's or newer CRT set at the curb, cut the donor set's HV lead at the fly, and unhook the cup from the CRT....That way I've got the lead and connector together.
Does your set have some kind of HV plug on the flyback end?...If so it could be difficult to properly change the HV lead without causing new problems.

[madlabs]

Been doing some playing and, of course, have more questions! First, foremost and very embarrassing but:

I think I may have thought of horizontal and vertical hold backwards my entire life. It would make sense with other learning disabilities I have. I have always thought that vertical hold when you adjust it the picture goes diagonally to left or right until you get the hold correct and then it is straight up and down and that horizontal hold is when the picture flips up or down. You know, the classic, common problem where the picture is part way down the screen and you see a bar at the top or bottom across the screen and when you get it adjusted right the bars disappear off screen. However looking at the way the controls on my set are wired and labeled, I must have that backwards. Straighten me out here! If that is the case, while I do have some height issues, vertical hold is my issue, not horizontal.

I swapped out yokes yesterday. One yoke is from my original set and the other from one of the parts set I picked up. The original gives a more egg shaped test pattern and is harder to lock in the vertical? hold. The other is damaged, has a crack in the housing and even a crack in the ferrite but gives a more oval test pattern and seems easier to lock in. It also affects a straight line across the screen, making it dip up a little on the right and down a little on the right, only near the edge of the screen. This effect is more pronounced at the top and bottom of the screen, meaning a straight line in the middle has very little of this effect but a line near the top or bottom does. There are a couple of HV ceramic caps on the yokes, might these be responsible for issues?

Thanks!

[Electronic M]

Vertical hold misadjusted results in horizontal black bar scrolling vertically. Horizontal hold misadjusted results in diagonal black bars.

The yoke and or the caps in it may be bad. No harm in swapping either.

[madlabs]

Well, as my Pappy always said, if brains were lard I couldn't grease too big a pan. I do actually have a little dyslexia/disgraphia so I'm not too surprised. And while it must be tough answering stupid questions like that imagine what it's like to be me.

So, pulled apart both of the yolks I have handy. Both measured about the same resistance on all the coils. Quite a bit of corrosion in both of them, it looks like the plastic disc that seperates the magnets from the housing is off gassing or something, both have yellow/white substance all over the place and a lot of corrosion on the metal disc. I noticed that the two yokes have different windings, one is larger than the other and may be a different guage. Just in case I replaced the resistors on the one I am using. There was a springy wire on the yoke that was on the CRT that I am using, the other had a wire to a paper that was under the CRT holder. So I made a reasonable facsimile and put that on. I also noticed that the horizontal linearity magnet was a little cocked and straightened that.

It's locking OK and is less egg shaped. What is the proper way to adjust the horiz. lin. magnet? In and out from the CRT but keep it even I assume?

Thanks!

[madlabs]

Ok, quick question: I replaced the HV lead to the CRT with a new piece of 20kV, 22AWG wire. I cleaned the contact on the CRT and hooked it all up. I have WORSE hissing than before and visible corona. I checked the HV output and it is 12.5kV or so. What gives? It's making me nervous and I can smell ozone.

[Phil Nelson]

Where is the corona, exactly?

Phil Nelson

[madlabs]

Up on the crt where the hv lead connects. It is primarily on the edge of the metal ring embedded in the tube. I did clean the area well, both for good electrical contact and then the entire area around the contact for soot and grime.

Thanks!

[madlabs]

Well, no good deed goes unpunished. I was putting the Predicta back together. It's been working pretty well, occasional vertical lock issue but only every once in a while. Just before stuffing it all back in the cabinet I checked it, working fine. Tucked it all in, put on the knobs, screwed it all down and wah wah wah....

Now I get a raster, sound but no pic. Tube troubleshooting guide says V4 and V14. Replaced V4, same issue. I bloody well better not be V14 (the CRT). I poked and prodded, unplugged and replugged, looked at tube sockets and I just can't see anything amiss or find anything loose. Gotta admit I was a little frustrated. Any suggestions?

[Electronic M]

Got scope? Look for a video waveform of appropriate amplitude at the CRT and work back to point of signal origin...It's probably something simple, easy and stupid.

[bandersen]

Make sure you plugged the CRT video wire back onto the right post.

Are you running it with the 21FAP4 ? Were you able to resolve the issues you were having with it ?

[madlabs]

I do have a scope, a Tek 465M but it has been acting up. I'll try putting it on there and see what I see. If I can get it done before I take off for my 48 hour shift I will.

I did check that the CRT video wire is connected to the right place and I do get a raster. This is with the 21FDP4 I got with a parts set that has been working pretty well. I have not yet resolved the issues with the FAP4, I had to clear off some bench space to work on a couple of things. Any ideas on that one Bob?

[bandersen]

You would get a raster even with the video wire disconnected. The signal on that wire modulates the brightness.

I'm wondering if socket was wired right for the 21FAP4. I see that you swapped pins 2 and 3 however.

The 21FDP4 has G1 on pin 3 and G2 on pin 6.

21FAP4 has G1 on pin 2 and G2 on pin 3

So you maybe needed to swap pins 3 and 6 rather than 2 and 3 ?

[madlabs]

Hmm. I get no raster with the video wire disconnected, just snow.

However, I have found the problem, it is with the video source. Fooling around with the DVD player got me a picture again. I think my BT modulator may be having issues, even with the video modulation cranked I don't get the over mod led lighting up. I'll have to dig into that. I did briefly hook my scope up to the video output and do get a somewhat similar to the Sam's waveform but it is jittering around too much to get a good look at. I may get bold and try to hook up my little digital scope when I get home from work Wednesday.

Thanks!

Bob, if I needed to swap pins 3&6 instead of 2&3 would I still get a correctly oriented picture? What I get looks right but is dim and weak with retrace lines.

[bandersen]

Raster means you have vertical and horizontal deflection. Nothing to do with snow or a blank screen. Glad you got it sorted out

Yes, you could very well get problems you describe if incorrect voltages were applied to G1 and G2 or if they were left floating.

G1 has the retrace blanking signal and G2 is the electrostatic focus voltage.