Recently Acquired 1969 Motorola Color Tube Tv

[Lain94]

Last winter I acquired a 1969 Motorola Color Vacuum tube tv. HT-617CW is the service model number. D20TS-921-D02 is the chassis model number. It appears to be a VERY high hour set from what I know about it. The color driver pots are turned ALL the way up. The tv has changed hands many times in its life. Was once used in a barber shop for awhile until 1990 when it needed repair work done on it. The person I got it from fixed it back in 1990 and ended up keeping it after customer would not pay up for repairs. It was in use throughout the 90s through the early 2000s then sat in a basement in humid Massachusetts until Late 2021 when I was given the tv by the now very busy and retired repairman.

The tv did work when I tried powering it up with a variac. No issues at first but when I turned the tv off I heard a loud "pop" sound and upon examining the inside of the tv their were two burnt carbon comp resistors with char rings around them, along with a ceramic cap that was burnt up (locating right at where the mains voltage comes into the tv) It looks like a filter cap may have bit the dust and open shorted. The #2 wire fuse on the top of the chassis is also burnt out and gone, no trace of it left. The circuit breaker fuse also tripped. I already replaced the two burnt resistors but obviously that is not all that will be needed to repair this thing. It looks like it was NEVER recapped at all in its life as far as I can tell.

I have been on a waitlist since January 2022 to get this thing fixed at a repair shop an hour away in Mass. I have virtually zero experience working on vacuum tube electronics of any kind. I am more used to working on vintage computers which is my main specialty. I am really eager to get this thing fixed but am puzzled as to why it worked fine when it was turned on with the variac gradually but it shorted somehow when it was turned off after a few seconds.

Any information at all about this tv or what may have happened is appreciated.

[Airedale]

It's a handsome set, I hope you can get it repaired.

[AlanInSitges]

That ceramic across the line looks fine. It should be replaced regardless.

Most likely what happened was one of those filters was leaky and overheated while it was powered on. It was coincidental that it finally vented right when you turned it off. You really need to replace the electrolytics in the power supply, the fuses, and that across the line cap, then power up again slowly. I'd probably check the diodes in the power supply first too. None of that is particularly difficult to do, so you might want to try that yourself and see how far it gets you.

[DavGoodlin]

That is a great set but very dirty too. Make sure all those tubes are tested, then you can tighten up the socket pins.

Clean all pots with DeOxit and rotate 25 times each. The lousy parts are few but generally, some of the electrolytics may be all you need.

Otherwise the 1967-68 Motorola sets are about as rugged as a Zenith.

[zenith2134]

Very very nice find. I would love to find one like that...way overbuilt in a good way.
Should be fun to work on.

[Electronic M]

I've got a virtually identical set. Mine came out of the basement of a reapir shop in Indiana and needed rust treatment and a cataract removal (mine was MUCH worse than yours). It needed a few caps (I think several of the lytics we're bad) some adjustments and a focus divider arcing fix.
These use the SODPIL single tube color demodulator so it's almost as simple as a monochrome set.

[Lain94]

Thanks to everyone for your comments and advice. I have to admit, when I first opened this tv up I was super intimidated by how complex it was and the rat's nest of wires and components under the chassis.

I am 27 years old so I never really grew up with vacuum tube tv sets, just the solid state CRT ones which look way less complex. It is mind boggling how much tvs have changed both in size and design over the last 50+ years.

The main reason why I had been hesitating to work more on this set was a combination of my lack of experience with anything vacuum tube related and just the fear of accidently messing something up or making the situation worse with the tv.

I get the feeling that these color table top tube tvs are hard to find, as I tried and tried to look for other similar sets and they seem to be nearly extinct. So I want to make sure that the repairs are done properly.

I have every intention and desire of getting this set fully restored to it's peak functionality. eg. getting rid of it's minor but annoying cataract, rejuvinating the high hour crt if possible or finding a replacement, cleaning the rust and dust off, recapping, ect. Basically give this thing the full TLC.

[Notimetolooz]

I wonder if you remember how you turned off the power.
Did you turn it off with the TV switch or did you turn it off with a switch at the variac?
The variac is a large coil, turning the power off to it can cause an inductive kick-back and produce a voltage spike. The voltage spike could cause something on the TV power input to short.

Trying to rejuvenate a color CRT is very iffy, there is a good possibility that it could make the CRT worse.

Color set can get out of adjustment and require a pattern generator to correct the convergence, etc.

When this set was produced a color TV was the most complicated electronic device in a home by a wide margin.

[Electronic M]

SS sets 1980 and newer are typically several times more complex than anything from the tube era....The difference is SS sets hide their complexity in integrated circuit chips and by encapsulating much of the wiring in the PCB. Tube sets every component is serviceable.

If your set is like mine it's a 25XP22 CRT (I forget if mine is a AP, GP or XP, but they're all interchangable) which is a major blessing. The 23" and larger console CRTs are MUCH easier to find than the 22" and under table model /mini-console CRTs. Basically all console sized delta-gun CRTs (and a good portion of table model CRTs) the same envelope size are compatible. They made delta gun rectangular CRTs from 1965-around 1980 when inline gun tubes replaced them in new TVs. There is one thing to be aware of in 1968 the US government passed a law changing CRT size measurement from the industry standard of glass bulb diagonal to being the diagonal measure of phosphor screen viewable area. So the same tube made in 1967 as a 25XP22 would be labeled as a 23VXP22 if made in 1969.

There's tons of worthless SS 70s consoles in ugly Mediterranean cabinets with compatible CRTs out there like Zenith CCIIs and RCA XL-100s (granted the XL-100 name lasted far past the end of the delta gun era). Zenith came out with black matrix CRT technology (calling it Chromacolor) in the 1970 model year and RCA and others soon licensed it, and it is a MASSIVE improvement in picture quality. The Zenith Chromacolor CRTs tend to be VERY long lived. I've upgraded some of my 60s sets to 70s Zenith black matrix tubes and it always makes a nice improvement in picture.

[Lain94]

Originally Posted by Electronic M

SS sets 1980 and newer are typically several times more complex than anything from the tube era....The difference is SS sets hide their complexity in integrated circuit chips and by encapsulating much of the wiring in the PCB. Tube sets every component is serviceable.

If your set is like mine it's a 25XP22 CRT (I forget if mine is a AP, GP or XP, but they're all interchangable) which is a major blessing. The 23" and larger console CRTs are MUCH easier to find than the 22" and under table model /mini-console CRTs. Basically all console sized delta-gun CRTs (and a good portion of table model CRTs) the same envelope size are compatible. They made delta gun rectangular CRTs from 1965-around 1980 when inline gun tubes replaced them in new TVs. There is one thing to be aware of in 1968 the US government passed a law changing CRT size measurement from the industry standard of glass bulb diagonal to being the diagonal measure of phosphor screen viewable area. So the same tube made in 1967 as a 25XP22 would be labeled as a 23VXP22 if made in 1969.

There's tons of worthless SS 70s consoles in ugly Mediterranean cabinets with compatible CRTs out there like Zenith CCIIs and RCA XL-100s (granted the XL-100 name lasted far past the end of the delta gun era). Zenith came out with black matrix CRT technology (calling it Chromacolor) in the 1970 model year and RCA and others soon licensed it, and it is a MASSIVE improvement in picture quality. The Zenith Chromacolor CRTs tend to be VERY long lived. I've upgraded some of my 60s sets to 70s Zenith black matrix tubes and it always makes a nice improvement in picture.

I checked the tv and the picture tube has a label on it that says "21GWP22" I am unsure though if this is the original picture tube that came with the set when it was new though.

[Lain94]

Originally Posted by Notimetolooz

I wonder if you remember how you turned off the power.
Did you turn it off with the TV switch or did you turn it off with a switch at the variac?
The variac is a large coil, turning the power off to it can cause an inductive kick-back and produce a voltage spike. The voltage spike could cause something on the TV power input to short.

Trying to rejuvenate a color CRT is very iffy, there is a good possibility that it could make the CRT worse.

Color set can get out of adjustment and require a pattern generator to correct the convergence, etc.

When this set was produced a color TV was the most complicated electronic device in a home by a wide margin.

I do remember turning the tv off directly on its own power/volume knob, the variac remained on and at the same voltage when the popping noise occurred in the seconds after tv was shut off.

[Lain94]

Originally Posted by AlanInSitges

That ceramic across the line looks fine. It should be replaced regardless.

Most likely what happened was one of those filters was leaky and overheated while it was powered on. It was coincidental that it finally vented right when you turned it off. You really need to replace the electrolytics in the power supply, the fuses, and that across the line cap, then power up again slowly. I'd probably check the diodes in the power supply first too. None of that is particularly difficult to do, so you might want to try that yourself and see how far it gets you.

Yeah that makes sense to me I figured it was a capacitor issue. I traced down the likely origin of the problem as being somewhere in the power supply circuit.

Diodes going bad? I did not ever think to suspect diodes could fail, were early diodes more prone to failure back then?

Also what are your thoughts on there being performance issues caused by all those old carbon comp. resistors? I know they are notorious for drifting upwards in value as they age. They are also noisy usually. The issue though is that carbon film resistors will introduced inductance into the circuit which I heard apparently may cause issues in a vacuum tube circuit. Is it worth messing with replacing all the carbon comps and if so what should I replace them with?

[dieseljeep]

Originally Posted by Lain94

I checked the tv and the picture tube has a label on it that says "21GWP22" I am unsure though if this is the original picture tube that came with the set when it was new though.

According to the pictures furnished, it looks like the original CRT. It's made by Motorola if the label shows an EIA number 185. That CRT wasn't that great!

[old_tv_nut]

Originally Posted by Lain94

Yeah that makes sense to me I figured it was a capacitor issue. I traced down the likely origin of the problem as being somewhere in the power supply circuit.

Diodes going bad? I did not ever think to suspect diodes could fail, were early diodes more prone to failure back then?

Also what are your thoughts on there being performance issues caused by all those old carbon comp. resistors? I know they are notorious for drifting upwards in value as they age. They are also noisy usually. The issue though is that carbon film resistors will introduced inductance into the circuit which I heard apparently may cause issues in a vacuum tube circuit. Is it worth messing with replacing all the carbon comps and if so what should I replace them with?

Shorting of electrolytics in the power supply could kill the diodes.

My approach to resistors would be to first see what circuits have problems and then test the resistors, rather than a blanket replacement. The small inductance of a spiral resistor is not likely to cause trouble unless it is actually carrying high frequency signals (IF or RF). In the typical case, resistors in these circuits are bypassed by small capacitors anyway. In tube circuits, stray capacitance can be an issue, so component placement and lead length can have an effect, again, mostly in the IF and tuner. So, I wouldn't worry about the resistor type in video and sweep circuits, but have a bit of caution when working in the IF and especially the tuner.

[Notimetolooz]

The most likely parts in electronics of that era is the electrolytic capacitors.
That is why the best thing to do is assume they are bad before applying power.
Semiconductors are easily damaged by excessive current or voltage. A tube can withstand an overload for a few seconds but semiconductors will die in an instant, often without making a sound or without any smoke.
Of course any part can go bad. Many times TVs or radios are retired because something went bad and the owner doesn't want to bother getting it fixed.

Yes, stay away from the IF and Tuner since you don't have the test equipment for readjusting them. An exception might be carefully cleaning the contacts in the tuner.