25 inch zenith picture problems

 

New member
Username: Rpsly

Lafayette, LA USA

Post Number: 1
Registered: Nov-05
I have a zenith that I bought in mid 90's and recently the picture is a thin line across the screen. Usually after about 10-15 minutes the picture fixes itself. and some times the picture stays a thin line across the entire screen. Can anyone help? thanks,
 

Silver Member
Username: Reinhart

Post Number: 122
Registered: Nov-05
"I have a zenith that I bought in mid 90's and recently the picture is a thin line across the screen. Usually after about 10-15 minutes the picture fixes itself. and some times the picture stays a thin line across the entire screen. Can anyone help? thanks,"

Your television likely has cold solder joints and possibly some bad electrolytic capacitors in the vertical scan driver circuit, usually in the vicinity of the vertical amplifier IC.

Service will entail circuit level work.

Discontinue use and shop around for repair services, if you choose to have your set repaired.

If you choose to replace it, consider donating the old set to a repair shop as opposed to simply throwing it away. In addition, buy your next set from a reputable Japanese brand. I personally would recommend Sony. - Reinhart
 

New member
Username: Rpsly

Lafayette, LA USA

Post Number: 2
Registered: Nov-05
how much trouble would this be for a beginner to fix. I know how to solder but I doubt that I could read a complex schematic.
 

Silver Member
Username: Reinhart

Post Number: 177
Registered: Nov-05
You don't need a schematic to deal with cold solder joints. You just need a good idea as to where to look for the ones that are causing you trouble and, maybe, fix a few that are starting to go but haven't yet.

Basically, visually trace the wires that connect the deflection yoke (something that looks like a funnel with finely wound wires wrapped aronud that's located behind the picture tube on its neck) to the mainboard and check within the vicinity of the yoke connection on the television mainboard. In the vicinity should be heatsinks connected to ICs. One of these ICs is likely to be the vertical driver amp; tracing any of the circuit traces from the yoke connection to any of the ICs close by will narrow it down.

Also, look around for labeling that may identify which part of the board has the aforementioned circuit, like "VERT AMP," "VERT IC," or the like. Also, it may not hurt to resolder any other joints around any other hot spots on the mainboard. Hot spots are characterized by a brownish-to-dark brownish discoloration. Look at the solder joints and reflow any that appear suspicious (dried-looking joints, cracking, etc.).

It's best to remove the old solder with a soldering vaccum or desoldering braid and then reflow the joint with fresh rosin core electronics solder of good quality. (I use RadioShack silver bearing solder) You can just simply reflow the joint without removing the old solder, though.

Of course, double-check your soldering to be sure you didn't cross-circuit anything. You don't want to power up a set that has a solder short and cause more damage, of course.

And, be weary of the anode cap. This is the cap that's on the top-back of the picture tube and is connected to the flyback transformer. This provides the B+ to the picture tube, which is about or over 25,000 volts typically for your size picture tube. The tube, especially if the set was used recently, will have a parasitic capacitance due to the fact that the tube deals with that much voltage.

You shouldn't have a problem with this since you don't need to deal with this for this particular repair, but if you remove the anode cap without first arcing the anode lead in the cap to the DAG ground (the bare wire stranding that's wrapped around the picture tube), you may set yourself up for a really big, nasty, and PAINFUL zap (it won't kill you as the amps aren't that high and it isn't like a mains capacitor on a microwave oven, but it will certainly get your attention).

Hope this helps. - Reinhart
 

RaviKGedela
Unregistered guest
Hi Richard,

Did you get to fix your TV?

I've some problems on my 25" Zenith TV (model number Z25X22). The picture is cut off on the top, bottom and sides. While watching football I cannnot see the scores on the top and while watching news channels the news bar on the bottom is stripped. What might be the problem? It was a cheap TV but hate to throw it away. Any way I can fix myself?

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