Flyback Failure

Yes,you do need vert. sweep to see the keystone effect.You may
be able to hotwire the vert.sweep section to the low voltage power
supply to get at least some vert. height so you can see a raster
and get a better idea of what's going on.It sounds odd that there
would be a .25 uf cap between the b+ line and the damper cathode.
There is usually a few thousand volts of rf on the damper cathode.
Usually the boost cap is between the damper plate and a tap on the flyback.
It's basically stacked on top of the b+ and the damper tube charges it up.
I would definitely change those caps.If you could post a partial schematic
of the horiz. sweep section that would be helpful.This sounds like a
very old flyback setup that uses a real transformer instead of the
more modern autoformer type flyback.The damper tube may not
normally have that much rf on it at all.The boost voltage may not
even be that much higher than the b+ normally either.Also check
to see if you have a doorknob type capacitor under the 1B3 socket
or somewhere else hanging off the hv line.These caps are known to get leaky or short out.
Regards,
Swanson

[Don Lindsly]

What happens when you remove the damper tube with the TV on? Is there any high voltage or boost?

When you disconnect the yoke, does the boost go up, down or the same?

Is the flyback running hot near the core?

Don

[nasadowsk]

If you pull the damper, everything stops. All the HV for the horz output and Vert sections are drawn through the damper.

I might see if I can 'hotwire' the vert just to see if it even runs. With that going, I can at least check the yoke.

I've not tried pulling the yoke, that's my next trick.

The flyback doesn't seem to get warm at all.

I'll try to get my hands on a scanner this week or next or soon, and scan in the schematic. It's quite interesting - uses 2 horz outputs and a few other fun features...

Try to get some answers and clues tonight later...

Thanks!

[nasadowsk]

Ahhh

I 'hotwired' the vert section. It boots weakly, but I didn't see anything that approached a keystone in the raster - it looked about as square as I'd expect.

I decided once again to measure the 340 supply (the main B+ for the sweeps) and found it...at 270. Hey, being 70 volts down could be a problem

I pulled the audio output and gained 5 volts. Joy. Looks like I've got to replace all the 'lytics too. The paper guys are comming this weekend, I'll get them then turn my attention to the electros. I've got a few temp ones I can jumper for now.

The flyback's ice cold. I'm guessing at this point I've just the classic bad caps issues here. I'll revisit the HV and all later on - the 130V supply for the RF/IF/Vid sections is a totally independant supply - I can pull the 5U4 to shut the big HV stuff off, and just get those guys up and running since they're likely gonna need help too.

I'm guessing, since I don't need the sweep stuff going when I check the set's alignment, that I can just pull the 5U4 to disable it all. Should be quieter and safer anyway.

BTW, the alignment proceedure on this set's a dream, just plug in a VTVM at one point, and apply signal at a few frequencies and peak/null a few coils, in order. They don't even really cover sweep alignment, just say to check for a waveform and touch up. I like this - I'm, not a huge fan of sweep alignment, even though it looks cool, I find they generally don't cover the interactions of the coils well, the desired curves are always tiny and not drawn to scale, and you need a ton of equipment to do it, unless someone makes a decent all in one alignment generator that's flexible enough to do old sets like this one....

Anyway, it looks like I gotta go through nd replace a bunch of caps and find out why I'm not getting 340, first. I thought I was, but I guess I misread the meter when I checked it the other day...

Well, looks like there's a light at the end of the tunnel - and heck, at 8-9kv, the CRT's not too dim, so maybe it's really good for a change. It's a Raytheon branded tube - nyone know how well they fair? Too bad it's not Sylvania - the two sets I've had with those were beyond good....

[Don Lindsly]

If removing the damper shuts everything off and eliminates all voltage on the damper cathode, then there are no shorted caps from boost to B+. The boost is usually filtered back to B+ instead of ground. That is to use 600 volt caps instead of 1KV caps.

Have you bridged the power supply electrolytics? What are the horizontal output screen and grid drive voltages?

Don

[Chad Hauris]

Don't even try troubleshooting till you replace those caps, it's a waste of time! Replace all paper caps and electrolytics.

[nasadowsk]

I disconnected everything from the 340V supply and hooked an ammeter up at the plate of the 5U4. Turning it up on the variac, I noticed that the *unloaded* power supply was nevertheless drawing about 15 - 20 ma!

Well, that's a good reason why the HV never gets up there with the tv running.

But, here's a weird thing - after letting it sit for a few min...the current started dropping, slowly but steadilly. Is this the 'reforming' effect I keep hearing people talk about? After a while at 340V, the current dropped drastically - down to like 2 - 4 ma. I suspect the lytics are gonners anyway, but this was neat to see in action.

I swapped out a few more caps - the big motherload of 'em comes in tomorrow.

Sucks my current job doesn't do board level, I used to be able to get 40mfd 350 and 400 volt caps at my last one

Looks like the big fun is gonna be replacing the lytics plus the pasper in the sweep sections (a lot are out already, but a few big ones aren't yet).

At least I established that the set isn't totally gone, and that's all I wanted to get at this point. With such an offbeat set like this one, I didn't want to go capping it only to find a dead flyback or yoke, though I guess there are subs out there anyway...

The recieving circuits are on a totally sepperate supply, so I can attack those while I wait for new lytics to come in - that one comes right up into spec, though I didn't check the AC ripple on it.

It's interesting though - one supply for the RF/IF/Video circuits, and another for the sweep. Did anyone else do this back then? It seems like a better idea than lumping everything in one supply...

Sounds like you are on the right track.Those paper caps are
old,paper,and highly suspect.Changing those caps will most likely
solve the problem.The yoke and flyback seem ok,let's keep our
fingers crossed though.Make sure you change the screen grid
bypass caps on the horiz. output tubes during your recapping
session.And when you take the caps out you could test them
for leakage just to see how bad they really are.If you have a
high voltage dc power supply you can use that to check for leakage.
As for the electrolytics,do they feel warm to the touch with no
load on the power supply?Even though the current goes down to 4ma,
that is too high if it is cap leakage and that means time for new
electrolytics.May the force be with you on your recapping adventure.
Regards,
Swanson

[polaraman]

7"estatdef I think this is for you! It is a Rogers replacement for Zenith 17233.

polaraman

[nasadowsk]

Well, I grabbed my 'test' electroltyic from home and jumpered it in to replace what existing can lytics I could. I also swapped out a few more caps. Slowly but surely I'm getting them all replaced.

I'm now able to get a raster and it's not keystoned at all. HV is still a bit low and focus isn't good, but the set's slowly getting better. I can hear audio from the set at times and the HV is getting closer to the listed value.

Slowly but surely, it's getting better. I think I'm getting maybe 10kv now and 14kv or so seems to be what the set's gonna need. The focus is bad, I think this is the coil adjustement, but otherwise I've got a decently bright raster even though the HV's a bit low.

The set's got potential!

It's got 4 IF stages, and 2 audio IF stages (!). With barely any antenna, it gets audio pretty clearly. Still looking for video though

Should be a fun set once it's done - probbably more watchable than my RCA KCS110A chassis - which needs a new 21CEP4 tube in it