More Zenith portable questions

[jmetal88]

I noticed a cheaper device being sold as a 'Digital Video Stabilizer'. Do you think that would work in this kind of situation?

[jmetal88]

Well, after watching it some more, the picture isn't as stable as I first suspected. It still slowly warps around, with spots getting larger or smaller, and is especially noticeable when a static image is displayed on the screen. I'm hoping when I finally decide to buy that new flyback that that will fix the issue. I assume it's the arcing I hear that's causing this phenomenon by causing the high voltage output to vary, but if there's something else that could be doing it, I'd appreciate any suggestions.

[DavGoodlin]

Dont overlook your HV cup that the 1K3? sits in. I have had those with pinholes blasted through. Open HV cage or just remove it, Lift the cup off the chassis.
Hold off on the fly though, it probably will not fix the flag waving on VHS. try the AFC diodes though.

[jmetal88]

Originally Posted by DavGoodlin

Dont overlook your HV cup that the 1K3? sits in. I have had those with pinholes blasted through. Open HV cage or just remove it, Lift the cup off the chassis.
Hold off on the fly though, it probably will not fix the flag waving on VHS. try the AFC diodes though.

Well, I did already try hot gluing the bottom of the socket where everything connects. That got rid of all the arcing I could see (although the filament winding was trying to arc through its insulation, too -- I took care of that with electrical tape).

As for the AFC diodes, I already replaced the selenium pack with two standard silicon rectifier diodes. Are those unsuitable for this purpose? Should I have gone with Schottky diodes like I've seen people recommend?

EDIT: I'm sorry, you were referencing the VHS problem. I kind of moved on to a different problem when I was talking about the picture locally shrinking or getting larger. It kind of looks like the shrinking and blooming due to brightness problem that all CRT TVs have, but it's doing it even when a static image is on the screen.

[jmetal88]

By the way, for the Schottky diodes, what reverse voltage and forward current would you recommend? 40V/1A seems most reasonably priced, but I don't want to put them in if that's not a high enough rating.

[DavGoodlin]

As for the Flag waving on VHS, VKer Cbenham has a cure: http://videokarma.org/showthread.php?t=257988&page=6
Some of my sets could benefit here.

[jmetal88]

Oh, that's interesting. I wonder which point I would solder that to on my set? I don't see anything in the schematic that's clearly labeled a 'filter', so I don't know what I would be soldering across.

I can upload an SVG trace I made of my schematic, if it helps.

EDIT: The grid of the 6EA8 tube labeled "Horiz. AFC" has a 1000pF capacitor to ground. Do you think replacing that with one of a larger value would have a similar effect to what cbenham is describing?

[Electronic M]

You've done two things that seem like EXTREMELY bad ideas to me.
First you tweaked the alignment without a TV alignment generator. It is nearly impossible to get TV RF and IF alignment right by eye alone, and nobody should EVER mess with it unless they have a good TV alignment generator, and oscilloscope, the factory or Sam's alignment instructions for the set to be aligned, and plastic alignment screw and hex drivers(if you use metal ones once you dial in an adjustment, the moment you remove the tool from the slug it will loose the adjustment you made, plus metal ones tend to crack apart and destroy adjustable cores).

Second it sounds like instead of cleaning the HV you just applied hot glue. This is bad on two fronts. Arcing can often be caused by dust and dirt building up and becoming a conductive coating...If that has happened(and you can't usually tell from looking) the glue likely won't do a damn thing to remove the conductive path formed by the dirt causing arcing. Lastly hot glue in the HV cup or almost anywhere on a chassis is a bad idea. The set will eventually get hot enough to melt the glue(especially that close to a tube), and you will have a big mess to deal with when it melts...Also you will have to deal with the the glue if you ever need to change the resistor in that socket or the HV/filament wireing going to it.

On most sets with a plastic HV cup there are two screws that hold the cup to the chassis, and two more that hold the socket to the cup. Remove them all, remove the cup, clean the everliving daylights out of the cup, clean and dust the socket and the cup mounting area, and reinstall the cup. This will solve most arcing issues commonly associated with an HV cup.

You said you wanted to change the HV rect filament wire and HV line to the CRT but could not find a suitable replacement. The cheapest and easiest replacement you can get is to find a 20" screen or larger 1980's-2000's CRT set at the curb or buy one for a couple of bucks at a thrift store/resale shop and steal the HV lead to the CRT from one of those newer sets(I do it and it works great). You may have to strip two sets to have enough to replace both the filament lead and the CRT HV lead. You can use the HV connector already on the lead from the newer set. Patching HV/HV rect filament lead with electrical tape is like putting a bandaid on a gun shot wound....It might help, but it won't stop the bleeding.

I don't mean to sound harsh, but it makes me sad to see you harming a set you seem to really want to have working properly through bad seemingly uninformed decisions.

[old_coot88]

Originally Posted by Electronic M

...I don't mean to sound harsh, but it makes me sad to see you harming a set you seem to really want to have working properly through bad seemingly uninformed decisions.

Ditto to your entire post. Sad. Wish he had some in-person mentoring for help with it.

[jmetal88]

I'm sorry man, but I'm doing the best I can with the knowledge and equipment I have. I got the set for free, and I hate to spend a lot on equipment to get it working. You're right that I don't have a lot of experience with high voltage equipment. I have it just *almost* perfectly working, and there are just a few small problems I still have to work out, so I kind of just started trying things.

As for the alignment, I just kind of figured I'd try to do it by eye, and if that didn't work (which it didn't, as I shattered one of the cores when I tried to turn it), I'd pipe in composite video. That's what I'm doing now, and it's working great. The point where I tied the video in is at the grid of the video output tube, which is supposed to be a 1V Peak-to-Peak signal, and is DC biased at -0.5V, so the composite video signal is close enough to work, there. I have the audio going straight into the volume control, which DC biased at 0V, but I think it's expecting a higher signal amplitude, as the output is kind of quiet.

I can pick off the hot glue (I've done it on a lot of things before) and clean the HV cup, as you suggested, and see how that works. I do appreciate the advice, even if you have to give it harshly.

[Electronic M]

I can understand where you are at. My first couple of restorations nearly drove me nuts before TV restoration clicked(and I had spent years working on tube radios prior to that) and my projects finally started to come out right.
A couple of additional tips ANY sharp or pointy edges on the solder contacts or leads going to the HV socket will cause arcing or corona discharge so if you change the HV rect wireing clip excess lead lengths and make sure to solder in big smooth blobs covering wire and component lead stubs completely as well as any sharp points.

As for the weak audio...You can use a cap .1uF or thereabouts should work to couple the line audio from your signal source to a point before the volume control and after the FM detector. If you connect the cap to the output of the audio FM detector that should give you the most volume.

[DavGoodlin]

Originally Posted by jmetal88

Okay, I took care of all the arcing I can see, but after the set has been left on for a while, I can hear a steady 'crackle' of arcing that I can't see anywhere, so the flyback may still be a problem. Also, I think I might need a new 'suction cup' lead, as I did actually see one arc shoot straight through the insulation on that thing, which is kind of worrying. Any suggestions on where I could find one of those?

That HV cup should be washed like a plastic dish, then do as I say below.
I did this to the flyback on my 1963 RCA Color roundie back in 1979, and when I fired it up about 20 years ago the HV came up without arcing.(it needs other work including a picture tube) Funny thing, 34 years ago, I assumed I would NEVER find a flyback for this set, so I stripped the arcing-tracked cover off the fly and brushed on about 6 coats of this stuff. I highly recommend it.

When in doubt, get the dope out and start brushing;..http://www.alliedelec.com/images/pro...S/70159781.pdf

Electronic M is right on..
Regarding unqualified alignments, I diddled my share of slugs to compensate for tuner, IF and video problems. I recommend getting a fact'ry schematic, scope, marker and sweep gen (Sencore speed-aligner) do it right. It always improves things. I will not tweak anything other than sound, burst or horizontal efficiency coils without the above equipment.

[jmetal88]

Alright, I cleaned up the HV cup, and I also did my best to smooth out the soldering on the socket (it wasn't pointy, but it did have a couple of lumps). I still hear an occasional arc, but it doesn't seem to be nearly as bad as it did before I put the hot glue on, even now that I've removed all the hot glue.

I'm still getting 'waviness' on static images. Is that just normal, or is there something I can do to get rid of that? It's hardly noticeable while watching an actual TV program, but if, for example, I bring up the menu on my VCR, I can see the text swell and shrink regularly, and it almost looks like there's banding of increased and decreased intensity that 'crawls' up the screen.

[Electronic M]

Could be bad lytics in the power supply.

Could also be bad fluctuations in your wall current. I have that problem, and it drives me nuts. My sets(when I run two or more at once) will rapidly and randomly bloom at the same time (lights also flicker in step to it)...A friend of mine experiences the same thing and thinks it is because of smelting operations running on the same power grid in the area.

[jmetal88]

Originally Posted by Electronic M

Could be bad lytics in the power supply.

Could also be bad fluctuations in your wall current. I have that problem, and it drives me nuts. My sets(when I run two or more at once) will rapidly and randomly bloom at the same time (lights also flicker in step to it)...A friend of mine experiences the same thing and thinks it is because of smelting operations running on the same power grid in the area.

Well, I replaced all the electrolytics with brand new parts I ordered from Digikey when I first started working on the set a couple of years ago, so I guess I'd suspect the wall current. Maybe I could replace the capacitors on either side of the main power choke with larger values and see if that works. 40uF and 80uF seem pretty small, to me, but those were the original values.