Zenith System 3 CRT help - Videokarma.org TV - Video

rtsherrod81 · #1 01-31-2021, 10:57 PM

Hello All,

I recently acquired a Zenith System 3 console TV manufactured December 1980 (1 month older than me). Paid $75 for it as the cabinet is in good shape and still had the ultrasonic Space Command remote. It had a bright raster when I "auditioned" it so I paid the guy and took it home.

When I first tried it out with a VCR connected, I got a bright image, but with poor contrast. Tonight I connected my new (to me) CR70 tester to the factory installed Zenith 25VFCP22 and put it to the test. It passed H-K and G1 shorts tests with good to excellent emissions on all three guns with great color tracking. This issue at hand is poor cutoff. The red gun is just off the low side of the cutoff box, while the blue and green are pegged at bad with the bias at -52V and the cutoff set fully clockwise. In the extended cutoff test with the bias set to -36V, the meter reads in the upper half to one-third of the meter.

Is there any chance of improving the cutoff using some method to restore this CRT? Should I try the Auto Restore function?

I'm open to trying anything no matter the end result as this will not be a daily driver, only used occasionally for retro gaming or watching old movies. If the CRT gives up the ghost, I will just part it out selling what I can and scrapping the rest.

Any advice will be greatly appreciated.

Regards,

Bobby

jbattles · #2 01-31-2021, 11:19 PM

connect a vcr and let it play 24 hours and see if the picture is better.

zeno · #3 02-01-2021, 03:47 PM

I will assume it uses a 9-160 HV module. Its the big one at the bottom with the
HV transformer.
Looking in the back on the right rear under the focus control there is a cap, 10mfd 315 V IIRC. Change it. Will cause your problem & others.
If you have to remove the board its easy when you learn the secret.
Let us know

Dont rejuve for now. Thats last resort & using clean & balance is better
& less risk.

73 Zeno

LFOD !

rtsherrod81 · #4 02-01-2021, 05:52 PM

Hello Zeno,

Yes, this does have the 9-160 HV module. I will look at replacing that cap. I need to see if I have any. If not, I will order as I have to place an order for another project.

Please advise on how to remove the board. I believe I read somewhere that there is a red retainer to remove.

Will the capacitor be enough? The at the bias setting listed in the set-up guide, -52V, I could not get cutoff. But with the bias at -36, no issue. Based on what I've read, given the good emissions, this is due to wear of the center of the cathode material and/or ion poisoning.

Also, I would not use the Rejuvenate function as that is very aggressive according to the manual. My thought was to use the Auto Restore which appears to much gentler by comparison.

Regards,

Bobby

John Adams · #5 02-01-2021, 06:21 PM

There are a number of NOS Zenith modules on EBay .

zeno · #6 02-02-2021, 03:51 PM

Hopefully..... Its a common fix on ALL brands from the late 70's on.
Causes any, some or all:
Pix to bright
streaking
Normal pix on left to bad at right
Jail bars
Retrace lines
Looks like bad CRT often.
and probably more if I thought a bit.

Removal depends on if its been done before. Stuff dont get put back !
Pull & throw away little black things at edge connectors.
Metal or plastic bracket from flyback to frame.
Red holder at rear under board.
Red key apx center of board. Twist 90 degs & pull out.
Push down little claws on each side of board on the frame. Slide back & out.

Quote:

Originally Posted by rtsherrod81

Hello Zeno,

Yes, this does yes the 9-160 HV module. I will look at replacing that cap. I need to see if I have any. If not, I will order as I have to place an order for another project.

Please advise on how to remove the board. I believe I read somewhere that there is a red retainer to remove.

Will the capacitor be enough? The at the bias setting listed in the set-up guide, -52V, I could not get cutoff. But with the bias at -36, no issue. Based on what I've read, given the good emissions, this is due to wear of the center of the cathode material and/or ion poisoning.

Also, I would not use the Rejuvenate function as that is very aggressive according to the manual. My thought was to use the Auto Restore which appears to much gentler by comparison.

Regards,

Bobby

rtsherrod81 · #7 02-02-2021, 10:46 PM

Hello Zeno,

Thanks again for the information. I have pulled the HV board and found the cap you were referring to. It is a 4.7uF 315V and it has been replaced at least once before as can be seen from below. Someone got a little overzealous with the soldering iron and lifted the trace.

I noticed a label on the board that states "RE MFG IN MEX BY ZENITH" which could explain the repair. Therefore this is not the original HV board.

I need to place an order for another project and I will include this cap. Are there any others I should get as a just in case? Is the installed cap the correct value?

Regards,

Bobby

zeno · #8 02-03-2021, 03:45 PM

The big black main filter cap is common. Yo get a little width problem at first.
Other than that cold joints are common especially the transformer.

73 Zeno

LFOD !

rtsherrod81 · #9 02-05-2021, 04:47 PM

Hello Zeno,

Do you know which Zenith service manual would apply to this set? Would it be CM-130?

I'm thinking about getting my hands on one for reference.

Regards,

Bobby

zeno · #10 02-06-2021, 10:01 AM

CM130 sounds close. Look for the one with K models. May also
refer to the XXX chassis or system 3. If there were supliments
you probably not get them, its the nature of the beast. Sams
also covers the set.

73 Zeno

dieseljeep · #11 02-06-2021, 08:06 PM

[QUOTE=rtsherrod81;3231220]Hello Zeno,

Thanks again for the information. I have pulled the HV board and found the cap you were referring to. It is a 4.7uF 315V and it has been replaced at least once before as can be seen from below. Someone got a little overzealous with the soldering iron and lifted the trace.

I noticed a label on the board that states "RE MFG IN MEX BY ZENITH" which could explain the repair. Therefore this is not the original HV board.

I need to place an order for another project and I will include this cap. Are there any others I should get as a just in case? Is the installed cap the correct value?

Regards,
Some of the soldering looks a little suspect!
BTW, I read a notice that came with a Zenith rebuilt 9-160 module that they wouldn't accept a module that had a trace blown off due to a lightning strike, as an exchange. It wouldn't meet standards as a U/L approved replacement part.
They never looked at them if they were packed in the box the replacement came in.
I never had one that was damaged that way!

zeno · #12 02-07-2021, 10:01 AM

I never saw the lightning warning & I have opened hundreds of them
over the yrs. Never had a dud inspected either.
Zeniths almost never got lightning damage. They use a VERY effective spark gap
between the the cold ground & both sides of the AC line. I have seen many that were burnt but no damage to the set. The points are very close & I would bet it
will ark over at a few hundred volts. Anyhows its on the 9-160 & the black wire
goes to it.

73 Zeno

rtsherrod81 · #13 02-14-2021, 07:27 PM

Hello Zeno,

I replaced the 4.7uF 315V cap next to the flyback/HV transformer as well as a 1000uF 80V cap that I think is for the degauss circuit since I had one. There was also a 4.7uF 315V cap on the neck board that I replaced for good measure. I'm planning on taking an accounting of the other electrolytic on the board to replace as well.

The picture seems to have improved. It is still a little soft and there is a little color bleed and streaking at times. The picture control (brightness?) is in the upper third of its rotation (CW) to get a good picture. The black level (contrast?) is at its midpoint. "Color Sentry" is off as I think the picture looks worse with it on.

When I turn the picture control beyond the point I have it set to almost max if not max, the picture obviously gets brighter but it blooms. This blooming is also noticeable with the controls set as previously mentioned when bright white text or scene elements are on screen.

I adjusted the focus to get the smallest "dots" on the screen with no signal. The focus control is in the upper quarter of its rotation (CW). I also checked the CRT anode voltage and it is at the 30 kilovolts specified.

Any other steps I can take to try to improve this? What is the "clean & balance you mentioned previously?

There is a Chromacolor II console for $60 about 1.5 hours away that is tempting, but I won't make a move unless this proves to not be worth continuing. Space is limited.

Regards,

Bobby

rtsherrod81 · #14 02-24-2021, 10:11 PM

Hello Zeno,

I now have a service manual for Zenith Triple Plus Chassis System 3 TVs. This is the CM-130 I mentioned before and is for L-Line. My TV appears to be a M-Line as the model (Service?) number begins with SM and not SL as listed in this manual. The manual does cover the boards that are found in this TV and I will read and study it thoroughly.

If you have a moment, please advise on the clean and balance you mentioned previously. Your help is greatly appreciated.

Regards,

Bobby

zeno · #15 02-25-2021, 05:00 PM

Double check the value of that cap, I could swear it was a 10mfd.
The screen shots look pretty good to me.
The color level is a bit high IMHO.
Try this. Run it for a week or two. See if it looks better at higher
brightness & picture levels. Leave the auto color off so you can adjust.
CRT's that havnt been used often get weak & need a wake up period.
Some start unwatchable but will come back nicely.
As far as clean & balance AKA auto restore dont do it unless you
try the above first.

The CC2 set is the easiest set to fix & learn on. Simple design, serviceable,
& truck loads of parts still out there. Wont give you the super brite &
highly detailed pix as a S-3 but in its time the best 25" sets.

73 Zeno

LFOD !