Recently Acquired 1969 Motorola Color Tube Tv

[Lain94]

I used Deoxit 100 to spray into the CRT socket and tube sockets...I think I screwed the tv up. I am now only getting a horizonal line that changes color but no vertical deflection. (Same symptoms as the Heathkit tv before it ultimately failed and now has no picture or signs of life) Does Deoxit 100 cause shorting?

I fear I may have ruined the heathkit tv and likely burned the yoke coil. I turned the motorola tv off. as soon as I saw the horizontal line. (It got to that point with normal audio when the variac was turned up to around 80ish volts or so) Normally the picture gradually expands out. Also of note is that I used 99% isopropyl rubbing alcohol to try and clean the grimy pincushion circuit board (The tv sat for several days so what little water was in the mixture likely dried off for sure), I wonder if it smeared grease around on the board and may have caused a short there. I am at a loss and pretty discouraged that the tv is now worse off than where it was before.

[Electronic M]

On tube TVs at least, you generally can't harm the yoke with loss of deflection. The CRT will typically be fine as long as you turn down the brightness, or catch it reasonably fast.
Vertical sweep failure will be cause by the vertical circuit, if you disturbed it look at what you disturbed, if you didn't then check voltages against schematic and report back with a comparison and we can help you interpret.

[zeno]

Check the service / normal switch first. It often gets bumped or dirty.
See how the CRT looks after set-up. If the blue looks bad you
can do a clean & balance to perk things up. I wouldnt go to
a full rejuve.

73 Zeno
LFOD !

[Lain94]

Ok, it looks like it was just a loose connection and I made sure all connections were secured this time. Vertical deflection is back. I tried my best to fine tune the rf signal i was getting from the digital to analog converter box. Also adjusted AGC, Contrast, brightness, horizontal sync, vertical sync ect. I also used my color king test pattern generator.

Based on the photos the convergence is way off and possibly color purity as well. But the most important issue to fix is the weird multiple images that seem to occur along the horizontal.

I am going to check the horizontal sweep frequency later with my oscilloscope and see that the horizontal sweep is at 15.75khz.

I suspect leaky caps in the horizontal circuit possibly. As for the lack of green color. This was later found to be a simple issue with the green video driver pot. on the drive board. It is just a bit finicky and I forgot to clean those. So green does work just did not realize the issue with that until photos were already taken.

https://imgur.com/a/ZcWcEWl

[Electronic M]

Pro tip for adjusting horizontal frequency with a scope: first scope composite video from a DVD player or other precise stable signal source, set the horizontal time axis of the scope for 2-3 horizontal sync pulses on screen (from this point on don't touch the time scale of the scope), count the divisions between leading edges of pulse tips, then hook the scope to the TV and adjust the TVs horizontal osc coil (hold pot centered if present) so the number of divisions between peaks is the same number counted with no signal applied to the TVs tuner...When you connect signal it should be locked without having to touch any controls after doing that.

[Lain94]

Also, should I be wary of whether or not the oscilloscope can handle the high voltages in the horizontal sweep circuit? This oscilloscope is one of those digital chinese ones you can get for around 100-150 bucks. I just did not want to fry the oscilloscope by feeding it voltages far higher than what it may be designed for. The model of this Oscilloscope is ADS1014D. The manual says it can handle up to 400V voltage continuous which is far lower then what voltages are likely to be encounterd in the horizontal circuit.

[old_tv_nut]

Originally Posted by Lain94

Also, should I be wary of whether or not the oscilloscope can handle the high voltages in the horizontal sweep circuit? ...

Definitely should be wary. Don't try to measure the horizontal output plate, the damper, HV rectifier, focus rectifier, or anything on the flyback transformer.

[old_tv_nut]

The exceptions that are OK to measure are lower voltage pulses like those for AGC or burst gate - but measure those in the circuits where they are used, not at the flyback itself, to prevent accidentally contacting a higher-voltage terminal.

[Lain94]

All diodes have now been tested in circuit using both my multimeter and my capacitor wizard (the manual claimed it could find shorted or leaky diodes in circuit).

All diodes seem to be ok, no shorts, none are open, and all are behaving as they should on the multimeter including the two that the sams photofact said to check if horizontal frequency is off. So that now leaves tube V8 as the last thing the photofact suggests checking. This is a horizontal oscillator tube the voltage levels going through this tube are far lower than from other tubes such as the horizontal output. Would it be safe to measure at one of the pin on this tube? Max voltage going through this tube per the schematic is about 275 volts, other pins on tube have lower voltages.

Should I suspect this tube as possibly being weak? Obviously heater is ok as this is a series string set and I doubt any shorts since that would cause other electrical issues and symptoms. The tube is 6GH8A. I do not have this tube but supposedly I may have some tubes that can substitute for it and have the same pinout and heater voltage and current such as 6EA8. Is it OK to substitute 6GH8A with a known good 6EA8 for this circuit and application to rule out a bad tube?

[Lain94]

Update:

Doh! I did not realize that the diodes X11 and X12 were germanium and not silicon ones. Most of the diodes in the tv are indeed silicon but these two are germanium. They are painted black on the glass which confused me. I pulled them both off the tv and noticed the voltage drop as being .50V to .60V for both of them during the multimeter diode function test which is way too high for germanium 1N34A diodes. Voltage drop should be about .3V

So I got two replacement germanium diodes which were the correct voltage drop and soldered them in place.

Also the 6GH8A tube has been tested by my recently acquired and working EICO 667 tube tester. The 6GH8A in this tv appears to be an original one. There is SOME leakage but not an unacceptable amount among the elements. The emissions are just barely in the red weak zone. I compared the emissions to a known good NOS RCA 6GH8A and sure enough the NOS tube had very good emissions and no short or leaks.

I replaced all three can caps as well at this point finally with quality nichicon ones, Hopefully this will all make a difference.

[Lain94]

Another Update: Well I think I made a mistake. Apparantly those diodes were in fact silicon ones. Apparantly a long long time ago a company made "Transitron" branded glass package silicon diodes....

The motorola tv has a total of three of these, two of which were x11 and x12...which I replaced with 1N34a diodes...

What is strange is the photofact part list says they are 1n34a which confuses me. Everything else on the part list matches up. The only things that did not were the lack of a remote control unit or FM/AM radio built in.

It is almost as if they later started putting in these silicon diodes instead of the germanium ones.

Any idea what this is all about?

They are glass painted black with a green arrow on one end and two yellow stripes on the other end.

I could find almost no information at all about these diodes on line and not a single image or photo of them aside from a very old black and white photo of one on a product catalog from the 1960s.

Here are some pictures of what one of them looks like.

https://imgur.com/a/20mRzIC

[ARC Tech-109]

I've seen those in the Japanese electronics from the same era, they're germaniums. Had a nearby lightning strike take out the chroma and phase detect diodes in my T940 Magnavox, got creative with some wafer sockets and 6AL5's to replace them.

[BeamT]

Can you identify the resistor that is burned in half just adjacent to the diode in your last picture? Looks like it might be a 33K (orange, orange, possibly a 3rd orange) You can see scorching in the area? Did I miss a reference to this in an earlier post?

Nice TV!

[Lain94]

Oh yeah that resistor was one of two that actually did get burnt and failed open. I had it replaced way back quite some time ago. I should clarify that these pictures are older ones I took of this tv the first time I actually looked at the chassis.

I think those two resistors either were already burnt or got that way back when I had that ceramic shelled wax paper safety cap fail way back. (This issue was fixed and was not too hard to fix once I realized what had happened)

[Alex KL-1]

Last year I acquired a delta gun TV, and at testing, I'm desperate due to lack of any image. And a faint image appeared with bias pots maxed out. I think the CRT was dead. But then I noted that the G2 bias caps are paper-in-oil, and I decided then to change it for polypropilene caps. Voilà! Image back, with great brightness, at middle of adjusment!
The bias normally have relatively high DC resistance, so bad caps can upset correct adjustment.
If you not checked yet, is good to check if cathode, G1 or G2 have messed DC voltages due to leaky caps or drifted resistors. Also serves for various other faults you have found or will encounter. Unfortunately, older sets are not so reliable like 80's+ sets...