Hi
Any new TV experts out there? I am currently working on a 4 year old Toshiba 27A32 TV set. It has reduced vertical deflection and a strange wiggley fold-over condition. I replaced the vert. out IC chip (LA78041) and all associated caps, and get no change. I am using Sam's photofact # 4671 but the set they show is quite different, but close enough and I also discovered some errors in their schematic. Can anyone make a suggestion on what else could cause this symptom? I attached a photo.
Thanks
Danny in Cleveland

shorted yolk perhaps? The wavyness might suggest that.

that's a scary lookin image. I've never come across a vertical problem that left the raster that distorted.

This looks more like a power supply problem rather than a purely vertical problem...is the sams similar enough that you can see what the voltages should be?

I vote for checking the power supply to see if correct voltages are there and are flat DC.

Hi and thanks for the replies...Yes the power supply voltages to the vertical circuit are on the dot according to Sam's. I flexed the board and wiggled the yoke leads and no change. This symptom used to occure after 5 minutes, now after the new parts were installled it comes on that way. The customer said taht it sometimes would shut-down. Yes, I thought of the yoke being bad also, how can one confirm this?
Interesting problem eah?
Danny in Cleveland

I been caught by a Toshiba set with a vertical fault before. I thought I'd replaced all the relevent caps. I had missed one that was nowhere near the vertical IC, but connected to it's input. That said I'm working without schematics more often than not and I doubt something as simple as a failed cap could cause such severe distortion.

Could the fact the fault became permanent after you installed new parts suggest a temperature sesitive component somewhere was disturbed in the process?

Have you checked the yoke with a shorted turns tester?

That IS bizarre. You say it's moving or wiggling? I would have agreed with the other guys who point a finger at the power supply. 99% not the yoke if it's moving. I would scope the B+ to see if there's noise or something making the B+ other than a clean DC. I had a Mitsubishi with a similar symptom, and it was a LEAKY B+ diode at the bridge! Very strange.

But if the main B+ and also the supply line to the Vertical IC looks clean, then I would start suspecting the yoke.

Charles

Great replies guys! I have a Heathkit flyback/yoke ringer I built about 175 & 1/2 years ago which should be able to test that newer yoke. I also think the real problem is in the power supply, which I will investagate further. A bad yoke would probably kill the set...how would I get a replacement if i needed one?
Danny in Cleveland

I did a DC resistance measurement of the vert yoke windings. I get 14.5 ohms, Sam's say it should be 8 ohms...but you never know with Sam's accuracy. If it has shorted windings woulden't the resistance be lower not higher?
While I'm doing TVs has any one heard of Randix TVs (has Goldstar CRT). I just found one in my neighbor's garbage a model CM 1330...not in Sam's. It got rained on so when it drys out I'll bring it up on my variac and see what's what.
Danny in Cleveland

It has to be a power supply, or horizontal deflection problem. Look at how the width is changing and the raster doesn't even fill the width of the screen in places. The vertical is probably powered from the flyback, so anything wrong with the horizontal deflection can also effect the vertical. I think the vertical problem is just a symptom of a different problem. Does the width problem move slowly up the picture, or is it random? If the distortion is slowly moving, I would suspect that 60Hz is getting into the power supply somewhere (bad filter caps, bad AC rectifier diode,...).

The only possible yoke problem I could see causing that would be a short between the horizontal and vertical windings.

I did a DC resistance measurement of the vert yoke windings. I get 14.5 ohms, Sam's say it should be 8 ohms...but you never know with Sam's accuracy. If it has shorted windings woulden't the resistance be lower not higher?
While I'm doing TVs has any one heard of Randix TVs (has Goldstar CRT). I just found one in my neighbor's garbage a model CM 1330...not in Sam's. It got rained on so when it drys out I'll bring it up on my variac and see what's what.
Danny in Cleveland

Maybe not shorted but 1 open. A lot of modern tvs put the top and bottom vertical windings in parallel. I had a Magnavox that had a weird distorted vertical problem and one winding was open. Can't remember if it look exactly like yours but it's worth a check. It was 10 years ago on my father's tv. The width may be affected by lack of a proper signal to the pincushion circuitry. You can unsolder the windings at one terminal and check each separately.Then you know whether the yoke is good or bad and whether the Sams is right or wrong.

Blah, this TV is made by Orion, so I'm not surprised to see this kind of problem.

I remember in the early '90's working on a Sears-Toshiba built set, and having a very similar problem as this set. Replaced all the caps, and the IC, and it still looked the same. Turned out, that there was a single odd-wad cap waay over by the tuner module (remember those?) that had really drifted, but looked OK, as the plastic had not shrunk, etc. Oh how I hated those Toshibas until I saw all of the strange layouts enough to be aware of them...

Thanks Guys
All indications are that the yoke is bad. All signals and B+ are fine. I think there is no hope due to the fact the yoke is part of the CRT and the whole CRT with yoke would need to be replaced. It's only 4 years old what a piece of crap. Not a very servicable set, now doomed to a land fill.
Danny in Cleveland

being a 27 inch set does it have a pincushion circuit. there could be your problem. there is nothing wrong with a orion tv. toshiba would not use them if they were bad. all i have worked on were great performers. steve

Unfortunately I think he's got a bad yoke. I hadn't seen a bad vertical section of the yoke for 10 years but I got one in today.Mine was a Magnavox 27" chassis 27F800. Looked identical to the one in the picture that was posted. I took loose one of the vertical windings at the yoke terminal.One section was completely open. The good section measures 14 ohms therefore it would measure 7 ohms if the yoke was good. Luckily it's a removeable yoke. I have a similar yoke from a 27" Magnavox with different terminals. I'm gonna try to save the set with that yoke.

If you can find another yoke, you could try to replace it. The hard part will be finding a compatible yoke to replace it with. The yoke has to match both the electronics and the CRT.

I have removed bonded yokes before so I could reuse the CRT in a different set. It's not that hard to do if you're careful. You have to disassemble the yoke from around the CRT neck one layer at a time.