Zenith TV Green (but not with envy!)

[dumpsterdiver]

I have a Zenith CRT Monitor/TV Model SLS2504EW, C-10 chassis. Awhile ago the screen went bright green with retrace lines. I replaced the green video output transistor with no change. Everything else works fine. My research says that one cause could be a shorted green gun in the CRT. Will a VOM show any shorts when I test the base pins or is it only at high voltages do the shorts happen ?

 

[KeepItSimpleStupid]

I replace a B/W (OK Green monochrome monitor) that had that same symptom. It was the CRT. Shorts were findable with an ohmmeter. I think it was a short to one of the control grids. It was too long ago. You should also be able to see a couple of voltages that are identical (the two pins that are shorted) and should not be.

So, first, I would measure the DC voltages on the picture tube neck.

 

[dumpsterdiver]

I used a meter on the pins of the CRT on resistance and not diode check and found no shorts. Only the heater shows continuity. As you suggested I measured voltages and no two were the same. Makes me think the problem is on the CRT neck board.

 

[KeepItSimpleStupid]

Sounds like a plan. Take a look at the datasheet for the picture tube, If you can post it, I might have some other ideas such as comparing the modulation signals.

 

[tvtech]

My biggest failing on Forums like this...I need to be physically working on it. Otherwise, my advise is useless...or at least it needs to be next to me. So I can physically see what is potting. Then I could maybe figure out stuff.

I can try now, but I would probably be wrong..and guessing.

People describe faults differently. Especially those that don't know what to look for. No offense to the OP.

Just the way I go about things.

Regards,
tvtech

 

[dumpsterdiver]

Looks like I "fixed" it. This set failed around 2006 or so when it blew the switching regulator. Replaced it and an electrolytic in the switching section and came back to life with the bright green screen at a time when I was barely employed and money tight. I did a schematic the hard way-from the board-because I couldn't afford a Sams or other docs. I found good docs later at the Central Library. It sat around serving as a side table for 2 or 3 years until the next time finances were better. That's when I replaced the green video output as I thought it was leaky. A few more years passed with an attempt or 2 to cure the green. Along comes life events and my apartments are closing so it's fix or dump time. My stupid mistake was not checking the focus and G2 earlier. I messed with the focus,G2 and screen controls while handling the board. Once I did a proper setup the green was gone and the picture returned to normal.

 

[killivolt]

Nice; I would on several occasions need to try and restore and clean up a shorted "Electron Gun"

Zenith Tubes were notorious for carbon build up. Sometimes it worked and only for awhile and then go out. Some taking the driver Transistor.

Been so long can't remember even how to do a fix on the old birds. CRT's are for the birds; I'm glad I can afford a flat screen.

Good job.

kv

 

[dr pepper]

You can get machines that attempt to repair crt gun shorts.

But you can do it a controversial way that back street repair shops used to do and use a 'bulb bopper', do a google for it.

I've seen a similar thing done with a power resistor instead of a bulb and it worked.