1990 Zenith System 3 - Page 2 - Videokarma.org TV - Video

andy · #16 10-04-2007, 10:18 PM

Quote:

Originally Posted by karmaman

By scan lines, I mean that when I look close I can see the individual lines that make up the picture and I can follow them with my eyes as they go down.

Then that's a good sign. When the CRT get weak they often get so blurry that you can't see the scan lines any more.

karmaman · #17 10-04-2007, 10:38 PM

Hey guys, I've got the TV hooked up to cable now and everything is great, but... this TV overscans horrendously. Most logos for all the TV stations are partially cut off and the TV Guide is unreadable..... is there some adjustment I can make that will fix this?

MRX37 · #18 10-04-2007, 10:47 PM

Some TV's are just built that way. However, I'm certain there's something you can adjust or replace that will fix that.

Is the picture distorted? (Do people/things look taller then they should?)

radiotvnut · #19 10-04-2007, 11:02 PM

Try adjusting R2112, the vertical lin control. It's located on the far right hand side towards the front of the power supply board. There could also be some bad caps around this control.

bgadow · #20 10-05-2007, 11:37 AM

I seem to recall that Consumer Reports would complain about Zeniths overscanning too much. I have a 13" Zenith from the late 80s and it does quite a bit. If it's just vertical then the adjustment should handle it.

andy · #21 10-05-2007, 11:49 AM

I assume you meant to say to adjust the vertical size control, not vertical lin? Do those sets even have a vertical ine control? Assuming is vertical overscan and the linearity is good, that may be all that is needed. There should also be a width coil near the flyback that will take care of any horizontal overscanning. It will be the only large adjustable coil in the set.

I have seen some other bad caps in those sets that caused excessive overscanning with poor vertical linearity. It's been a long time, but I think they were at the edge of the board near the vertical IC.

radiotvnut · #22 10-06-2007, 12:27 AM

Quote:

Originally Posted by andy

I assume you meant to say to adjust the vertical size control, not vertical lin? Do those sets even have a vertical ine control? Assuming is vertical overscan and the linearity is good, that may be all that is needed. There should also be a width coil near the flyback that will take care of any horizontal overscanning. It will be the only large adjustable coil in the set.

I have seen some other bad caps in those sets that caused excessive overscanning with poor vertical linearity. It's been a long time, but I think they were at the edge of the board near the vertical IC.

My schematic indicates R2112 as a vertical linearity control. I can't find a vertical size or vertical height control anywhere. Here are some cap suspects if adjusting this control does not solve the problem:
C2108 - 4.7 uf
CX2109 - 1000 uf
CX2110 - 100 uf
C3248 - 3.3 uf
CX3208 - 4.7 uf (bi-polar cap)

The "X" in the location number indicates these caps to be critical values and should be replaced with a cap of the same capacitance value and at least the same working voltage. Those caps in the 2100 series stand out in my mind as being possible suspects. CX3208 is a big cap located at the front of the power supply board. All the rest are located around the vertical linearity control and the vertical output IC. This IC is a 13 pin device mounted on a heatsink.

R3249 is the Horizontal width adjustment in this set. Look towards the left hand side of the power supply board. You'll see a larger size electrolytic cap. Behind the cap is a small transformer. Behind that is a small electrolytic cap. Behind that cap is the horizontal width control. Behind the control is the vertical IC heatsink.

karmaman · #23 10-06-2007, 12:34 AM

Thanks for the suggestions! After watching TV on the Zenith for two nights, I've noticed the overscan problem is not so much Vertical as it is Horizontal. The Vertical seems to be OK, overscans just a tad bit but is still perfectly acceptable. Horizontal, on the other hand, seems to be causing the problem. I'm also getting some pincushion distortion on Horizontal. I'll try adjusting the control tomorrow, any suggestions on caps in the Horizontal section that might be bad?

karmaman · #24 10-06-2007, 03:58 PM

Here are some pics of the TV. I'll add some pics of the chassis when I open it up to make adjustments tomorrow.

karmaman · #25 10-07-2007, 11:52 AM

I'm almost certain there are some bad caps in the horizontal section, the picture has started shrinking horizontally for a split second and then going back to normal. I'll replace the three 2100-series caps in Vertical later today after I go to Fry's, plus any suspect caps in the horizontal section if you reply before I leave for Fry's.

MRX37 · #26 10-07-2007, 12:41 PM

Caps are cheap. I'd say replace as many as you believe are suspect.

Having a multimeter to test the caps would help narrow down which ones are really bad. Failing that, you can't go wrong with replacing suspect caps, unless you replace them with ones of the wrong value or too low a voltage rating. Your TV is pushing 20 years old. Likewise, the caps in it are pushing 20 years old.

andy · #27 10-07-2007, 12:48 PM

With any Zenith, check for bad soldering. I've never seen a Zenith circuit board that didn't have at least a few bad connections. Also, look for leaking caps. Zenith sets of that age had some with bad seals. Look for a brown substance on one of the wires under the caps. You might have to remove large caps to check them. The high temperature ones are particularly bad (brown, or dark blue cases).

This is where an ESR meter would be really handy.

RaymondLeggs · #28 10-07-2007, 03:58 PM

Quote:

Originally Posted by karmaman

By scan lines, I mean that when I look close I can see the individual lines that make up the picture and I can follow them with my eyes as they go down. Every single tube TV I've ever seen does this, I know it's normal but I don't know what it's called. Anyway, this will become my main set. I can finally replace the Orion 13" I've been using for so long! To think I was about to buy a trash Durabrand from Wal Mart.... I knew they were garbage, but thought it was my only option for getting a large TV for my room.

I have a symphonic flat tube TV that is now marketed under the durabrand name that has an exelent picture that eats LCD's for breakfast butthen again its bigger than "13".

karmaman · #29 10-07-2007, 09:59 PM

I changed CX2110, a 220uf cap behind the heatsink the 12-pin IC is mounted on, and a random 1000uf cap on the left module. No change at all, I'll replace the rest of the suspect caps you told me about as soon as I have money. One thing though, I'm buying the new caps from Radio Shack, they are Xicon caps (are they any good?) anyway, some of the replacements have the same uf rating and higher voltage ratings, but are physically smaller than the original caps..... is this normal or a cause for concern?

MRX37 · #30 10-07-2007, 10:47 PM

I think as long as the uf rating is equal to the old caps, and the voltage is equal or better, you should be fine. If the spacing of the leads is a different length then the old caps, you might not be able to get the cap flush with the board, but it should still work, as long as it's the same uf and equal or better voltage.

As to the quality of Radio Shack caps: I haven't heard any horror stories. My only gripe is their price and limited selection.

EDIT: If you could somehow get ahold of a multimeter, it would make finding the bad cap(s) a lot easier.