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#1
09-22-2006, 07:24 PM
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Late model Toshiba 27A32 vertical problem
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 
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#2
09-22-2006, 08:19 PM
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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.
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Jordan
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#3
09-22-2006, 08:41 PM
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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?
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#5
09-22-2006, 11:25 PM
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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
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#6
09-23-2006, 01:00 AM
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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?
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#7
09-23-2006, 02:11 AM
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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
__________________
Collecting & restoring TVs in Los Angeles since age 10
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#8
09-23-2006, 11:07 AM
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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
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#9
09-23-2006, 01:54 PM
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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
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#10
09-23-2006, 02:34 PM
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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.
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#11
09-23-2006, 08:36 PM
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Quote:
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#13
09-24-2006, 10:26 AM
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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...
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#14
09-25-2006, 11:57 AM
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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
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#15
09-25-2006, 03:23 PM
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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
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