Zenith TV vertical deflection problem

My girlfriend has a Zenith B27A11Z TV, made in 2000, that has a vertical deflection problem. It started as the vertical deflection going out from time to time, and if she tapped on the TV it would come back. So I said OK, it's probably just a bad solder joint, maybe I can look at it sometime. But I never got around to looking at it. Now she says that tapping it doesn't fix it anymore. Sometimes turning it on and off does, but sometimes that doesn't work either and if she turns it on and off too many times it stops working altogether until she unplugs it. Now I'm wondering whether it's really a bad joint. Of course, she still wants me to look at it. So, are there any particular points or components that are known to go out on this model, so that I can hopefully get this thing over with as soon as possible?

Reply to
Jim Shaffer
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Probably still solder connections - both at the vertical output IC and at the deflection yoke plug. Should have been tended to sooner - the bad solder connections can kill the IC, but it sounds as if the connections just got worse since there is still full defection sometimes at turn-on.

Mark Z.

Reply to
Mark D. Zacharias

der

I remember that there was a series of Zeniths a few years back in which a diode in the vertical circuit would become flaky. It would check good with an ohm meter as I recall but would fail intermittently. I think it was a black high speed switching diode like an NTE 506 about a 1 watt size near the vertical IC. Lenny. .

Reply to
captainvideo462002

this is an exact scenario which demonstrates the idea you should NEVER nurse along an intermittent fault, the reason being that as time goes on what starts as a simple cheap fix ends up in a complicated mess. Chances are, other components and even the power supply have been stressed through repeated powering up and down. tell her to get it checked right away!

-B

Reply to
b

I finally got time to work on the TV this weekend. Prodding the plug and the vertical output chip didn't produce the symptoms. Prodding the HOT did, but only after the set had been running for about an hour. So I re-heated the connections, and it ran for about 3 hours with no problems (although I didn't prod it.) Then it started acting up again, same problem as before. (It doesn't completely lose vertical deflection, I misunderstood what she told me; it shrinks to about half size and jumps.) Putting pressure on the HOT's heat sink so as to push it towards the outside of the board makes it work properly, but only so long as pressure is maintained.

So, what do I try next? Should I have completely removed and re-soldered the HOT? Or do I have a bad HOT since it only acts up when it's been running for a time?

Reply to
Jim Shaffer

a blanket resolder of the line and frame stages is called for. That heatsink is flexing the pcb so it could be any one of dozens of joints in that area. check also the connections to the scan coils (yoke) As you suspected, it's best to remove old solder from the HOT and replace, though i doubt this is your problem. you can make a desolder braid effectively with some old 75 ohm coax cable dipped in solder flux.

work with a good lamp and check the PCB print for any cracks.

-B

Reply to
b

a blanket resolder of the line and frame stages is called for. That heatsink is flexing the pcb so it could be any one of dozens of joints in that area. check also the connections to the scan coils (yoke) As you suspected, it's best to remove old solder from the HOT and replace, though i doubt this is your problem. you can make a desolder braid effectively with some old 75 ohm coax cable dipped in solder flux.

work with a good lamp and check the PCB print for any cracks.

-B

Reply to
b

The HOT is the Horizontal Output Transistor. It drives the horixontal yoke and flyback. If you are having vertical issues... then the HOT is not the area that you should look at.

If the hot is bad.... then it would be excessively hot or blown.. If it was blown, your set wouldn't even power up... If it was excessively hot, then it would blow before 3hrs was up.... or even sooner. If the HOT was the problem then you'd have artifacts in the other systems of your set, like noise in the speakers... unable to lock onto channel... CPU malfunctions from the noise on the data lines... perhaps causing the channels to change by themselves or spewing jibberish onto the OSD or even killing the settings RAM chip.

Check the resistors in the vertical circuit. If they are damaged, the that could cause the issue... especially after heating up.. and especially for those little chip resistors on the underside of the board. Get the data sheet for the Video Jungle chip and find the Vertical Output pin. Replace capacitors in that circuit between the VJ and Vertical Output. If the vertical circuit has a trimmer pot, clean it, notice it's position and turn it left, right then back to it's original position... Replace the capacitors in the Vertical Output section. Wiggling the HOT headsink and creating the issue doesn't indicate that you vertical issue is in the horizontal circuit. The stress you put on one edge of the board will cause flexing on other parts other than the HOT.

BTW: The collector of the HOT is usually the mounting hole for the transistor to the heat sink.. And depending on the transistor used and the quality of the mica insulator that might be behind transistor... that heat sink could be holding 165+ volts or more just waiting for you to make that one mistake of touching two places at once.

My advice is to forget the HOT if your TV is powering up and running for 3hrs. The problem is not in the horizontal circuit. Reflowing that circuit does nothing but waste solder and iron tip time.

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Reply to
Anonymous

I once fixed a Magnetbox with intermittent vertical tearing, turned out to be a loose crimp on a tiny pot. Sometimes components fracture or stretch with age, not just solder joints.

Reply to
George Jetson

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did you look for the diode? Lenny

Reply to
captainvideo462002

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