Another question about Zenith Disc caps.

[Eric H]

This is in a Zenith Flashmatic, chassis 20X20Q, it works pretty well but the vert linearity isn't quite right, the height and lin controls are all the way at the end of their range and while it's watchable it's not quite right (heads are squished)

I suspect items M8 and M9 (vertical integrator per Sams) might be the problem, these are 3 legged disc capacitor looking things.
Sams shows them as a resistor across the outer legs and a cap? to ground?
but no values are given.

They both appear to have 87. written on them, one has a green dot the other has a yellow dot.

Can I build them out of individual parts and if so what values should they be?

[Steve K]

Eric:

The 87 is Zenith's designation for an integrator. Is there a 4 or 5 printed on the other side? The Zenith manuals do not give values either. I had a bunch of these at one time but I can't find them here so I suspect that they are still in my supply in Wisconsin.

Steve

[Eric H]

Hi Steve, they have the same 87. on both sides.

According to Sams the resistor part is across legs 1 & 3 but is the center leg a capacitor? and if so does it go from leg 2 to legs 1 & 3?

[wa2ise]

Originally Posted by Eric H

Hi Steve, they have the same 87. on both sides.

According to Sams the resistor part is across legs 1 & 3 but is the center leg a capacitor? and if so does it go from leg 2 to legs 1 & 3?

What they probably did was make one plate of the cap the resistor element, and the other side of the cap was the plate to center leg. Thus creating an infinite resistor-capacitor filter circuit. Using 2 or 3 resistors in series, and 3 or 4 caps to recreate it should work, if you know what the values are supposed to be...

[Findm-Keepm]

Originally Posted by Steve K

Eric:

The 87 is Zenith's designation for an integrator.
Steve

Yes, the 87 is the prefix for an integrator. Zenith lists 8 integrators in my 1974 parts listing/price list. 87-1, 87-4, 87-5, 87-7, 87-8, 87-9 (replaced by an 87-8), 87-10, and 87-11. Sorry no values listed. I'll see what I have in my used bins - hopefully something in there. Are there any numbers on the reverse of the discs?

Cheers,

[Eric H]

Originally Posted by Findm-Keepm

Yes, the 87 is the prefix for an integrator. Zenith lists 8 integrators in my 1974 parts listing/price list. 87-1, 87-4, 87-5, 87-7, 87-8, 87-9 (replaced by an 87-8), 87-10, and 87-11. Sorry no values listed. I'll see what I have in my used bins - hopefully something in there. Are there any numbers on the reverse of the discs?

Cheers,

Hi Brian, the numbers are the same on both sides but I wonder if the dots of paint mean anything?

One is green one is yellow, possibly a 4 and a 5 using the standard color code?

[Eric H]

I sent of a request to Moyers for the Discs, meanwhile I did some experimenting.

I clipped in some test leads across the resistor section of the integrators, I ran the leads to the top of the chassis so I could try various values and see what happened.

Since I measured around 80-100 ohms across the circuit to start with i installed a couple 220 ohm resistors across the discs, not a dramatic difference but it did change the picture some.

To make this short(er) I got down to 33 ohms across the discs and the picture has good linearity, the controls are still near the end of their range but the picture is very watchable.

The first picture is the set with the extra resistors installed, nearly perfect picture, the horizontal linearity is very slightly off but not bad.
(the "letterbox" effect is caused by the test pattern disc and not because the picture is too short)

The second pic is the set without any resistors installed, not bad but the picture is adjusted too tall to compensate for the bad linearity, if I adjusted it to the right height the top would be squashed.
I also noticed the Vertical lock seems much more solid with the resistors in place.

If worse comes to worse I guess I can add some resistors to the circuit and let it go at that.

[Eric H]

Got the linearity problem pretty much licked though it meant replacing an .033cap with an .047 to get the height control back to center instead of at one end.

The integrators were not bad, I replaced them with individual parts but it made no difference at all.

I don't know why I had to change the cap value to get it to work right, everything seems to check out OK but it just wouldn't work like I wanted it to.

Made a quick video of it running.
The background noise is a TV in another room.

http://www.vintagetvsets.com/videos/zflash.wmv

This is using the like new CRT I was given, it doesn't use an Ion trap and was much easier to set up!

[Tube TV]

Great to see it working , I will look through my canadian info and see it there is any values listed in there .

If there is I will post them here .

[Boobtubeman]

On an unrelated topic Where would one get one of those test pattern CDs?
Someone have a DVD recorder and could burn me one? All my stations out here run bar patterns or run all night with infomercials. Not like the good ole days when i would get up at 5am and await the station sign ons to adjust my tvs to. Need to do some touch-up on the Packard Bell i restored..

Steve

[Sparky]

I have changed many having been a Zenith shop, and they did go bad. I still have a few NOS ones buried somewhere. Taken from another forum, I cannot take credit, here are the values:

87-4 R= 33K C= 680pf

87-5 R= 47K C= 680pf

87-7 R= 68K C= 680pf

87-8 R= 82K C= 680pf