Recently Acquired 1969 Motorola Color Tube Tv

[Electronic M]

Originally Posted by n8nagel

Interesting. My only experience with "really" old stuff is two receivers from the early 60s, which mostly used the axial "ceracaps" not the disc types like you're thinking of and a few electrolytics. I have been told by different people that the ceracaps are usually good and also that they're garbage, answer depends on who you talk to LOL. All I actually know is on my H.H. Scott receiver one of the ceracaps just got replaced because that and a couple weak tubes were what was keeping the MPX from working correctly. Most PIOs in audio land are actually for speaker crossovers and there they tend to have indefinite life. I don't think I've seen many films in tube gear, only more modern solid state stuff and again in speaker crossovers, so they don't get exposed to really high temps unless they're in a power amp and even then they're usually away from the output transistors.

PIO caps in tube gear are usually Japanese made and usually found in Japanese made TVs (Motorola used some Japanese made parts as it was trying to get friendly with Matsushita), and they tend to be bad (electrically leaky).

The tubular ceramics were made by a variety of companies across 3 decades. I've seen some sets where they were fine and I've seen some sets where they were open or shorted. In GE Portacolors they tend to explode and spray bits of conductive foil all over the circuit board. In the newest application I'm familiar with Zenith 22-5001 safety caps used in CCII TVs of the 70s they're used in the flyback circuit and when they open they cause the HV to skyrocket, and if they short they trip the breaker on the TV...

[Lain94]

Originally Posted by ARC Tech-109

The mod was easy enough, just a couple of those wafer sockets and some thin wire. Follow the basic diode cathode & anode connections and find 6.3v to run the heaters. The thing about the 6AL5 is there is no junction "breakdown" voltage, they will forward conduct at once there is heat on the cathode with only a few pf of capacitance. The only downside if you will is the heater to cathode capacitance and the need to decouple the heater itself beyond a few MHz.

The real b**ch of the lightning strike is it was roughly a mile down the road but it followed the telephone trunk and found its ground at my QTH killing several pieces with the EMP as the Magnavox was not even connected to anything at the time, it took out all of the germaniums for the chroma, phase det and the diodes in the AM/FM stereo tuner (combo set)

There were a number of variations of those japanese germanium diodes, some had a low forward while others were twice as high being they were stacked internally. A silicon diode has a forward bias of 0.72v while germanium is 0.3v at its knee point, I don't recall the number for those glass diodes you have but they were like lice in the early 70's stuff from the likes of Panasonic... they were everywhere.

"Pure germanium is known to spontaneously extrude very long screw dislocations, referred to as germanium whiskers. The growth of these whiskers is one of the primary reasons for the failure of older diodes and transistors made from germanium, as, depending on what they eventually touch, they may lead to an electrical short." (Givargizov, E. I. (1972). "Morphology of Germanium Whiskers". Kristall und Technik. 7 (1–3): 37–41.)

Germanium whiskers? Never heard of them, I learned something new today! I have heard of tin whiskers though and how they are a problem in particular with many old pots in electronics and can cause at best an annoying intermittent popping sound from shorts, or at worst cause a chain reaction of issues. I always knew germanium transistors were more prone to fail than the newer silicon ones. I also knew germanium transistors would blow up but I did not realize that germanium could grow whiskers!

I will look over the old tvs I am working on to see just how many germanium are in these tvs and test them all.

[Lain94]

Originally Posted by Electronic M

PIO caps in tube gear are usually Japanese made and usually found in Japanese made TVs (Motorola used some Japanese made parts as it was trying to get friendly with Matsushita), and they tend to be bad (electrically leaky).

The tubular ceramics were made by a variety of companies across 3 decades. I've seen some sets where they were fine and I've seen some sets where they were open or shorted. In GE Portacolors they tend to explode and spray bits of conductive foil all over the circuit board. In the newest application I'm familiar with Zenith 22-5001 safety caps used in CCII TVs of the 70s they're used in the flyback circuit and when they open they cause the HV to skyrocket, and if they short they trip the breaker on the TV...

Yeah sometimes they do actually work and are ok, it is kind of a gamble. I don't believe that wax paper ceramic caps can be reformed at all like electrolytics can they? Regardless after seeing what happened to one in my motorola, and how it just suddenly blew up and flung ceramic shrapnel out the tv....yeah I will never trust those caps ever again. Ceramic safety cap fool me once, shame on you old wax paper safety cap. Fool me twice? Not gonna be a second time for that lol.

[Electronic M]

Originally Posted by Lain94

Yeah sometimes they do actually work and are ok, it is kind of a gamble. I don't believe that wax paper ceramic caps can be reformed at all like electrolytics can they? Regardless after seeing what happened to one in my motorola, and how it just suddenly blew up and flung ceramic shrapnel out the tv....yeah I will never trust those caps ever again. Ceramic safety cap fool me once, shame on you old wax paper safety cap. Fool me twice? Not gonna be a second time for that lol.

Paper dielectric caps typically don't reform, and even if they do is it really worth the risk?

[Alex KL-1]

Originally Posted by Lain94

Germanium whiskers? Never heard of them, I learned something new today! I have heard of tin whiskers though and how they are a problem in particular with many old pots in electronics and can cause at best an annoying intermittent popping sound from shorts, or at worst cause a chain reaction of issues. I always knew germanium transistors were more prone to fail than the newer silicon ones. I also knew germanium transistors would blow up but I did not realize that germanium could grow whiskers!

I will look over the old tvs I am working on to see just how many germanium are in these tvs and test them all.

I've heard about this: https://nepp.nasa.gov/whisker/anecdo...tor/index.html about these transistors. According with this investigation, the can is responsible for wiskers in classic old transistors, but I don't know if germanium is also responsible in some form/model also.

[ARC Tech-109]

Tin whiskers were job security for the GE MASTR guys as they would grow in the front end castings and short out the helicals causing the receiver to go deaf. They also used germaniums in the EP38A10 regulator section and they would often go on strike without warning taking the +10v supply down.

[kvflyer]

Originally Posted by Electronic M

Paper dielectric caps typically don't reform, and even if they do is it really worth the risk?

What he said... ^^

[Lain94]

Update as of last night: Primary issue of the "triple image" still not gone but performance of the TV is notably improved in other areas. Also decided to leave the NOS RCA 6GH8A tube in and just hold onto the old weak motorola one for now. Used deoxit on ALL the vacuum tube sockets and any other connectors or pots I could reach.

Then tested all the tubes. Confirmed that the only weak tube was the old 6GH8A all other tubes emissions are good and compared with known good NOS tubes. Cleaned the tv a bit more just for fun and my own satisfaction.

After completely recapping and replaced all of the three can caps with new capacitors and replacing the two diodes with 2 NOS germanium 1N34As:

1. It started right up just fine with no signs of trouble after replacing the stuff mentioned.

2. Horizontal triple image issue still is there but not any worse off than before.

3. The CRT picture tube can get way brighter now! Like WAY brighter in response to the brightness control on the front! WOW

4. Colors appear more vivid and pop out so to speak which was unexpected.

5. Fine tuning neon lamp indicator suddenly came back to life and now is always lit red the whole time. Should go out when fine tuning is correct. I know how to adjust the responsiveness of it and will do so later.

6. CRT makes a more satisfying sound when turned off suggesting a more thorough discharge when being turned off.

Conclusion: I am going to finish replacing remaining old electrolytic and any other remaining paper oil caps as well in the tuning and convergence circuits and any where else. I am also going to investigate the degaussing circuit further as it is obvious to me that it is not working. Appears to be controlled by some sort of relay.

Degaussing loop itself i measuring at 8ohms. Resoldered the antenna leads going to back of tv for a more solid connection.
Next will check diodes more closely once more, as well as focusing on old carbon comp resistors i the horizontal oscillator and AGC circuits for any that might be out of value range tolerance wise.

Beginning to suspect an issue with resistors or perhaps even a coil somewhere.

[Lain94]

Wow! Ok Apparently It must have been a leaky capacitor. I replaced the capacitor on the CRT driver board and the small electrolytic capacitor on the pincushion circuit control board. I also used deoxit and cleaned the two pots on the pincushion board for the vertical and horizontal. I believe one of the pots even had some tin whiskers which I wiped off and blew out the others with some compressed air.

I tried to rotate the pots a bit to get them loosened and cleaned and tried to put them back where they were. They likely still have drifted a bit for sure and will need more adjustments later.

Put the old 6GH8A tube in as well before turning on just out of curiosity. Finally also replaced one of the carbon comp resistors in the horiz. osc. circuit and while it measured out of circuit as 6% off value when it should have been 5%, it is possible that value went up even more at operating temp.

Still amazing at how well the convergence is despite it not having been adjusted since 1980.

Now to fix the degausser and get it working again, then onto recapping remaining electrolytics and any other problem caps. Primarily the one in the FT1 circuit, an electrolytic on the conv. board. some caps in the tuning circuit ect. Cleaning tuner and pots of front controls as well.

Some photos showing the progression of the picture as the tv warmed up and from me adjusting controls.

https://imgur.com/a/wzbJ6sp

[Lain94]

New Update:

Finally figured out how to get the tuner out and freed. Instructions were there the whole time on a rather dirty sticker on the back of the HV cage. Felt a bit silly after unscrewing every single screw but oh well.

I realized there were still some remaining paper oil capacitors in this tv, 2 were Jenson branded, one being 1uf 600V and the other being .47uf 600V. I am betting these are leaky and bad. I will replace those with mylar ones.

I also removed and recapped a small electrolytic that went from one of the lower control pot posts to ground. Used deoxit on remaining controls and pots and inspected everything. All bulbs look good but thought of replacing them anyways with 6.3v LED ones. Would it be ok to do so since the voltage is the same? or would the lower current draw somehow cause an issue? I would rather replace them with LED ones now to avoid having to open anything up later.

Then I recapped a cardboard shell electrolytic capacitor 100V 80uf with a 100V 100uf one. From what I understand it is ok to go same or higher with voltage. This particular one was in front of the horizontal centering taps in front of the HV cage. I figure it will be ok for a slightly higher capacitance.

Also realized one of the electrolytic capacitors in this tv is actually non polar. The non polar electrolytic cap is on the convergence circuit board. I am unsure what to do. I have a polarized electrolytic of the same value ready to go but even if it is ok to put in I will need to make sure it is going in the right way. Any ideas of what to do about this?

https://imgur.com/a/72zuFuE

[Yamamaya42]

A non polarized electrolytic capacitor is used when the circuit is primarily AC, biased with little or no DC voltage, so using a polarized one would be quite detrimental.

[Alex KL-1]

From some old makers datasheet, for "normal" electros I see that is possible to use with <10% rated voltage in reverse; ie. a 63V cap will survive to a "-6.3V" according with this. And this applies to a superimposed AC also.
If AC+DC is less than this rule of thumb, I think that is possible to use. Or at least for testing.
In fact, I accidentally prove it sometimes
Note: the maximum AC current is also to be in account, but is unlikely to be too high on a normal TV subcircuits.

[Alex KL-1]

Originally Posted by Alex KL-1

From some old makers datasheet, for "normal" electros I see that is possible to use with <10% rated voltage in reverse; ie. a 63V cap will survive to a "-6.3V" according with this. And this applies to a superimposed AC also.
If AC+DC is less than this rule of thumb, I think that is possible to use. Or at least for testing.
In fact, I accidentally prove it sometimes
Note: the maximum AC current is also to be in account, but is unlikely to be too high on a normal TV subcircuits.

Of course, will be a waste of big size capacitor, but at least, guaranteed for testing.

[old_tv_nut]

Another thing to try for replacing a non-polar electrolytic cap is to get two polar caps, then wire them in series with opposite polarity. However, this may be a problem in high-current applications like the convergence circuit. Better to be safe and get an actual non-polar replacement.

What value and rating is this cap?

[Lain94]

Originally Posted by old_tv_nut

Another thing to try for replacing a non-polar electrolytic cap is to get two polar caps, then wire them in series with opposite polarity. However, this may be a problem in high-current applications like the convergence circuit. Better to be safe and get an actual non-polar replacement.

What value and rating is this cap?

The capacitor has a rating of 30uf and 25VNP with a tolerance of 20%.

Removed it already to test, and while the ESR was ok, I then used a simple capacitance meter that runs on a 9V battery. It measured the capacitance as being WAY out of spec like a bit over 300uf! Yikes!

Definitely bad.