Avante On/Off issue
 

Here's an odd one and I'm not sure where to start.....

Months ago I turned off the SC (which I believe is short for Space Command) thinking it would turn off the heater in the CRT, but found out it didn't. I left it that way and was turning it off and on by pressing the small button under the door. With off, there was no on/off, volume or channel selection. This was fine for awhile, but I decided to turn it back on. Now the remote will change volume and channel, but not on/off the set. So I pushed the button on the panel and it didn't turn off the set. I switched the SC back off, but the button still won't turn the set off. I unplugged the set and upon plugging back in, the set is on. No matter what position the switch is in, I can't turn the set off.

Anyone familiar with this circuit? I'm sure there's nothing fancy about it and maybe the SC switch is going bad and not activating the power button on the front panel?

Anyway, I'm going to dig into the SM, but was hoping the brain power here could shorten my search.

Thanks!

Could it be this simple? I'm guessing not as nothing ever is, but you never know. According to the SM, it's a ceramic capacitor. I wish there were all the electronic places around now as they were when I was younger. I could be out and back with it in less than 30 minutes. Now I have to order and pay shipping. Need to keep a running list of components I want/need so when times like this come up, I have a full order to make it a bit less painful.

I keep a big box full of old PCB ewaste for this. Usually can just find something in there if it's just a onesie-twosie.

A .01uf ceramic will say 103 on it. Very, very common on lots of boards. Should be able to use a film or lytic there as long as it's 100V.

Depending on where it is in the circuit it could just be an optional snubber/spark suppression cap and you might be able to run with it disconnected. Some space command CCIIs have a solid state power switch that can short or open.

Chromacolor IIs almost always have instant on for the CRT and almost never allow you to switch it off. 2 solutions to that are unhook one of the instant on transformer wires, or unplug the set when not in use.

There is a post about the trac. I would look there
for starters. My serch dont work or I would look. Probably a yr or 2 back.
Zeno

Now I am upset I didn't keep more boards from scrapped equipment.

I am currently unplugging when not in use, but there are some other issues that seem to be part of the circuit. When I plug it in, the image is unstable, but tapping the power switch clears it up. Seems to also cause vertical hold issues until tapped. So it would seem I need to try replacing the capacitor in hopes it clears it up. If not, I need to find the entire circuit and find the fault.

What, exactly, should I be searching for?

Okay, I think I found the thread(s) you are referring to. The service manual didn't have the remote control board in it, but I found an addendum that does, so I found the board in a pic I took years ago and will have to remove the board and replace the capacitor noted in the troubleshooting PDF. If that doesn't work, can someone explain the triac and if that's something replaceable, or is it no longer available.

I pulled the 2 ceramic capacitors off the remote control board and tested them. Both are .01uf 100V. The markings on them are AVX .01 Z 100V. When tested, one is 7.8 and the other 8.1. The new capacitors read 10.1 and 10.2. Is it safe to assume the Z on the OEMs means they have a tolerance of +80 and -20%? If that's the case, the OEMs are about 20% out of spec, but does that mean replacement was/is necessary? Is there some other test I can do on them?

I know the best thing is just to change them, but I'm trying to add to my knowledge and make sure I understand and am doing things correctly. That and I want to make sure it's fixed before reinstalling.

No joy. I replaced capacitors as noted in the troubleshooting PDF and it didn't work. Set still needs to be unplugged. When in auto mode, I can change channels, sometimes volume and never power. In manual mode, when I plug it in, it is on, but the screen is wobbly until I tap the power button. It is then stable, but if I tap it again, it wobbles. So I think it is trying to remove power, but can't successfully and that's the wobble? I'm not sure what else to try. I want remote usage, so fixing would be nice.

On the bright side, the volume control is now clean and working as it should and so are all the other pots for color, tint, etc. Wasn't a complete waste of time.

If anyone has any suggestions on what to test on the remote board, please let me know.

I don't know how I missed this, but there is another "fix" in the troubleshooting PDF. It seems more likely as on/off is erratic as sometimes it turns on or off from the button and in auto, the volume doesn't change with the remote. I'm attaching the "fix" and the part of the schematic. They seem to be 22uf/10V. I have those as well as the two 10uf/16V. Since I'll be doing those, I'll need to get a 220uf/50V as well since I should replace all electrolytics.

So I have two more questions. The two 10uf capacitors I have are non-polarized. Going by the schematic (attached) it seems they go to ground. Can bipolar be used in this way?

Also, I just noticed from the pics I took of the tuner assembly where the remote control board is mounted, it seems the remote board has either been modified by the factory or afterwards. In the pic I see what appears to be an axial capacitor with yellow lead covers and something with 2 screws in it. Also, the paste from the triac is all over the place. I know I didn't do that while removing it as I would have noticed that stuff on my hands. Anyone ever see something like this? Can't be a bypass as it was working with the remote. There is an axial capacitor on the board just past the triac, but it is a 2uf/15V and the size of what's in the pic would have to be a much larger value going by its size.

Well while I didn't fix the remote control issue, I did manage to fix another issue that has bugged me for years. I no longer have jailbars! In the past I changed the diodes on the HOT and around the horizontal circuit as well as replacing the horizontal module. Nothing worked. So it is one of two things I did in this latest repair attempt. It is either the cleaning of all the control pots or rerouting the convergent board wires to more match what I saw in a pic from another set. Either way, they are gone!

But of course this can't be without another issue. Seems the the rerouting of the wires has thrown off convergence as it is has noticeably gotten worse on the right side and top as well as, to a lesser degree, around the entire image. I also am noticing color blotches around the bottom left corner and the right edges. Could this be a color purity issue or maybe it needs to be degaussed? If it needs degassing, how can I do that without a degasser?

I also think I need to readjust focus as the moire effect is more noticeable.

I'm attaching an image of the screen showing the lack of jailbars and you can kind of make out the color blotches.

Mine wouldn't turn on -- this is the thread about it: https://www.videokarma.org/showthread.php?t=276998

And here's some information I found about how this circuit works - from TAB books - Zenith Color TV Service Manual - volume 3.

I'm going to pull the tuner assembly again, but this time remove the remote control board so I can replace all electrolytics, test transistors and clean up the triac.

The pics you posted from those books seems to be a year or so newer as they talk about 4 volume positions over the old 3. Makes me wish I had that as 3 position volume always seems to leave it too low or too loud. It also noted something about staying in the powered down mode when plugged in. Mine is just the opposite. With the power issue, I cannot turn it on or off, but pulling the cord and plugging back in always has the set on. Other odd thing is once I plug it in and it's on, I do have to push the power switch as the screen is shimmying and the channel number is fluctuation in brightness a bit. Once I press the power switch, it stops and a second push brings it back, etc. So I'm hoping it's the caps on the remote board that are connected to the trigger circuits of volume and power.

When I get around to fixing the no-power issue on my 1980 remote CCII I may have to analyze that circuit and see if I can add a switch to make it default to on when line power is applied as it's plugged into a switched outlet that comes on when my basement signal rack gets power...The non-remote CCII it replaced was left switched on so if I saw it running I knew my signal rack was on (I could also choose what material was on screen by watching it).

When the power switch or remote power isn't working, it is always on when plugged in. I know when it is working again as when I plug it in, it is off and I need the remote to turn it on. Of course after this, the remote no longer turns it off and in manual the power switch doesn't turn it off, so I unplug it. Since it is intermittent, I'm hoping it's failed capacitors. My guess is the triac will either work, or it won't. Not sure about the optocoupler. I figure that since it's from the early 70s, it's not an LED inside.

I've finished recapping the remote control board. The smaller trigger caps had high ESR and were around 25% above value. One was 75% below (2.2uf read .52). I also decided to recap the audio board since I had everything to do it.

I cleaned up the triac and found they they used 2 mica insulators (mistake at factory?) and a ton of thermal paste. Guess they didn't believe in using it sparingly. The way the stuff hardened, and the amount, I'm sure it was acting as more of an insulator than a transfer. I don't have any of the white thermal grease, but I do have a tube of CPU thermal paste. I'm sure it will be better than the stuff from 50 years ago. Also going to use a ceramic insulator instead or mica.

Well it's done and reassembled. It turns on and off as it should. Also, recapping the audio board helped with a background static you could hear when volume was low.

I'm attaching a few pics of the cleaned up and reattached triac (I cleaned off that little blob on the side), the two capacitors causing all the trouble in the trigger circuit, the capacitor that was 75% of it's value that seems to be a decoupler in the volume circuit of the remote board and in the same pic you can see the optocoupler.

As a side benefit, now when I use the volume control on the remote it changes level with no crackle/static type noise like before. It's quiet and smooth in level change.

So far I'm quite happy with fixing these issues. This along with the jailbars being gone, it only leaves me with one last issue. I need to figure out how to get the setup function fixed so I can properly set the G2s. Otherwise I'll just keep it as set by a B&W image and always wonder if it's set optimum.

Thanks for all help and advice. Without everyone here, this might not have gone as well as it did.