Zenith CC2 avanti horz chassis - Videokarma.org TV - Video

DaveWM · #1 03-31-2014, 03:14 PM

Noticed lately that my avanti picture is not as sharp as I think it should be. The CRT test strong picture peak is working, the focus pot has to be turned fully one way and never really goes into focus and out again. I do not recall if its fully CW or CCW. the plan is to pull the back and get my simpson 260 on the focus pin (it goes up to 5kv if that is not high enough I can use my HV prob) and 1st see if its on the low or high side of the pot. From there will have to see what next. I did buy a new focus voltage divider just in case it is the problem.

the pot works as far as turning changes focus just seems to run out of range.

I wonder if the CRT socket/pin could be an issue? I have seen corrosion on those before (at least on some color crt's).

DaveWM · #2 03-31-2014, 03:19 PM

I can see a 4.7 meg resistor 2 watt resistor to ground, if that has opened up some I imagine the focus voltage could be too high, hope that is the case, will know for sure when I see which side of the pot the wiper is turned to.

andy · #3 03-31-2014, 04:08 PM

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Electronic M · #4 03-31-2014, 04:32 PM

Quote:

Originally Posted by DaveWM

I can see a 4.7 meg resistor 2 watt resistor to ground, if that has opened up some I imagine the focus voltage could be too high, hope that is the case, will know for sure when I see which side of the pot the wiper is turned to.

If the BIG HV divider has drifted high you can compensate for it by adding series resistance to 4.7M 2W. I did that on a CCI hybrid I own, and after it drifted a couple of more times in the following year(which caused me to bump up the added series resistance), it found a stable good point that it has sat on for the last three years.

DaveWM · #5 03-31-2014, 05:14 PM

well its too high, the focus pot is max CCW min voltage on the pin. So I will start with the 4.7 meg to ground, if that is not it I have a new divider to try.

Not really looking forward to getting to it since the service saver is pretty well blocked off by the fiberglass pedastal.

dieseljeep · #6 03-31-2014, 06:57 PM

Quote:

Originally Posted by DaveWM

well its too high, the focus pot is max CCW min voltage on the pin. So I will start with the 4.7 meg to ground, if that is not it I have a new divider to try.

Not really looking forward to getting to it since the service saver is pretty well blocked off by the fiberglass pedastal.

Does that set have the 800-860 focus divider. IIRC, the kit always included a 4.7 meg resistor, in case, the focus wouldn't adjust properly.

DaveWM · #7 03-31-2014, 07:37 PM

600M with tap at 70M I have 63-9895, no resistor in package. I can't imagine how far off the 4.7 meg to ground would have to be to have an effect on the control. Pot is a 15 meg. as mentioned I could prob put a 100meg resistor across the 70 meg IF it has gone high.

radiotvnut · #8 03-31-2014, 11:12 PM

Some versions of that chassis used an NTE526 tripler that contains the focus divider inside the tripler. On sets that have the seperate tripler and focus divider, it is possible to replace the original tripler and focus divider with the newer NTE526 tripler.

dieseljeep · #9 04-01-2014, 09:10 AM

Quote:

Originally Posted by DaveWM

600M with tap at 70M I have 63-9895, no resistor in package. I can't imagine how far off the 4.7 meg to ground would have to be to have an effect on the control. Pot is a 15 meg. as mentioned I could prob put a 100meg resistor across the 70 meg IF it has gone high.

When I was buying Zenith parts, the 63-9895 focus divider was always sold as a kit, known as a 800-860, that included a 4.7 meg resistor, the divider and an insulator sheet. I seldom used the 4.7 meg resistor.

DaveWM · #10 04-01-2014, 10:41 AM

oops just double checked the bag, its a 63-9896 not 9895, maybe the only diff is the resistor?

dieseljeep · #11 04-01-2014, 11:00 AM

Quote:

Originally Posted by DaveWM

oops just double checked the bag, its a 63-9896 not 9895, maybe the only diff is the resistor?

I'm trying to go by memory.
It's well over twenty years ago, since I bought and replaced one.
I know that some of the other make sets, where I found bad multi-megohm focus pots. I quit repairing sets sometime in the early 80's.
Now, I just collect and repair my own sets.

DaveWM · #12 04-01-2014, 11:06 AM

yep I hope its not the 15 meg pot. The pot adjust thru the entire range, which I hope means its ok.

If its the divider I will need to figure out how to connect it to the CRT anode, I am assuming there is a part that pushes out of the rubber cap that I can then solder the new wire to (it has two leads one to the tripler one to the divider)

dieseljeep · #13 04-01-2014, 12:05 PM

Quote:

Originally Posted by DaveWM

yep I hope its not the 15 meg pot. The pot adjust thru the entire range, which I hope means its ok.

If its the divider I will need to figure out how to connect it to the CRT anode, I am assuming there is a part that pushes out of the rubber cap that I can then solder the new wire to (it has two leads one to the tripler one to the divider)

If it's one of those clear vinyl jobs, remove it from the CRT and you'll see a set screw at the terminal. Just loosen the screw and pull the lead out.

DaveWM · #14 04-01-2014, 12:17 PM

roger that, thanks for the tip.

zeno · #15 04-01-2014, 03:30 PM

There were a bunch of different part ##'s for the dividers.
IIRC none of the ones in the solid states crossed to the 800-860.
The 800-860 was used in hybrids. The only difference was
the HV was 30 KV on the SS sets & 25 KV on hybrids, again IIRC !
Someone must have an old Zenith parts book to look it up.

Also be sure ALL the 22-5001 caps are orange. They eat up the dividers
first then the CRT socket. Each one that opens gives you +2 KV
of HV, there are 5 of them IIRC.

Sorry for the IIRC's but its been YEARS & I was on the bench so
didnt have the pleasure of doing may flat chassii !

73 Zeno