Motorola Color Television
 

I recently got this Round Tube Motorola Color Set in Iowa. It is a model 21CT220AW. I was curious if anyone had a similar model. Also I have a similar model that also uses the SAMS Folder 739-3.

Ross

I don't own this particular set but I think have seen the photofacts. If it is like the one I am thinking of it has a "hot" chassis and series filaments which is unusual for a console set. It also has dual horizontal output tubes and combines the 3.58 oscillator and chroma demods in one tube.

Clean looking set! That's the first 60s roundie Motorola I've seen. Before, only saw the pictures of the roundies from the 50s.

Have you been able to fire it up yet? How does it play?

Great looking set! I haven't EVER seen a Motorola roundie. They were so quick to have a square tube that there can't have been very many sold. Does yours work?

didnt they design the 23egp22?

sharp looking set. I too have not seen an motorola round set from this era. Im sure captianmoody really likes that set, he is into motorola as much as I am zenith.

Nice set! Almost impossible to find around here though. My electronics teacher had the exact one, His was a '64 model.
He wouldn't part with it as it was his parents first color tv.
Of course that was in 1980, Maybe I should look him up and see if he still has it....

I recognize that control set-up from an Art Margolis TV repair book. Never could figure out what kind of set it came from.

Thanks for solving a mystery that has haunted me since I was 13. (Perhaps that was a bit over-dramatic? ):D

Does Motorola use PC boards or wiring like a Zenith? Just wondering 'cause that's my favorite Zenith feature.

That set uses a metal chassis with point to point wiring like a Zenith.

Picture of the back of the set
 

Guys,

Thanks for the replies. Here is a picture of the back of the set.

Ross

Yes, it looks very Zenith-ish. Even has the service-saver test points on top of the chassis. But a series/hot chassis? Thats a bit of a letdown. :(

It is parallel wired.


Ross

Ross, I must have been mistaken in thinking your set is a series filament set, but there is a very similar model that is a hot chassis color set w/round tube, which was probably made as a cheaper alternative.

I have tried it out.
 

I tried the TV using a variac and had it on 60 volts for over an hour. I had to turn off the variac at 105 volts because I still had no picture or sound and one of the Horizontal Output Tubes was glowing cherry red. The first thing I guess that needs to be done is to replace all of the electrolytics? Then retry plugging in the TV with the variac?

Ross

Hi Ross,

Sounds like your Horiz Oscillator isn't working.
Check to see if the tube is lit, try wiggling it a little, could just be a bad connection.

If none of that works you could try replacing the paper caps in the Horiz Oscillator circuit first and see if that gets it going.

Eric

Correct me if I am wrong, but aren't you suppose to remove the horizontal tubes before bringing it up slow???

Thanks
 

Eric,

You were right about the horizontal oscillator not working. I replaced the horizontal output tube that was not glowing cherry red with a new tube and now I got a picture as shown but it disappears slowly and it sounds like there is a high voltage hiss in the high voltage cage where the 3AT2, 1V2 and 6BK4 are located.

Ross

I personally don't use the variac trick---have not personally noticed an improvement on electrolytics using it. If you use it you should remove the horiz. output tube as there is not enough drive signal from the oscillator at the reduced voltage, therefore not enough bias voltage is developed in the HO tube and it overheats.

The hiss is probably from insulation breakdown, one likely culprit is the HV rectifier filament leads.

I've only been using a variac for a short while to bring a chassis up slow. So far, I haven't noticed any improvements on lytics, but, it has helped me locate a few that were evidently shorted. I would get the juice up to about 40 or 50 volts, and usually find at least one lytic to be pretty hot. I would then change the hot one before taking it any further. Probably saved me from having a nasty surprise. Before having a variac, I was usually always leery of plugging in a set for the first time.

HV Hiss
 

Ross,

In addition to Chad's suggestion, you might also try examining your flyback very closely. I have a flyback in a set right now that has a hissing HV leak at the flyback. There is only a tiny little pin hole in the insulation that has a slight burn mark. Wasn't very noticeable at first glance, but when I got up close, I found it. I was going to put some silicon caulk on it, but every time I go to WalMart, I forget to pick some up.

Charlie, it looks like you are right about a hole in the flyback. I have a small cut in the flyback. However now I got a new problem from wanting to make sure the picture tube socket pins were free from corrosion. One pin broke off the socket and if you insert it in the hole it will make contact per my VTVM. How can I repair the problem? I have pics that show the damage.

Thanks,

Ross

Ross,

The photo you are showing looks as if the the WIRE came out of the socket (if i am looking at that correctly)... you had mentioned the PIN breaking off.

If the wire came out, here's an idea. Take a fine hacksaw blade and try cutting the tip off the rivet from the backside of the socket. If the saw blade is to thick to work under the rivet head, you could try using a pocket knife to bend the head up just a bit so you can work the saw blade on it. Another choice might be using some small wire cutters to get up under there and snip it off (although you may end up ruining the cutters after that). Once you get those heads cut off, then you can take the two socket pieces apart to resolder the wire back in.

Once you've made that repair, you'd probably have to go to the hardware store and get some really small screws with nuts to put it back together.

If that isn't going to work, ya could obtain another socket with the wires intact and cut that old one off and splice the replacement on. If you don't have another one, I'm sure that i have one around here I could send ya.

Anyone else here have a suggestion? I would think this has happened to at least a few of us in the past.

If possible, Drill out the rivets and replace with like. On the flyback, Make sure any carbon is removed from the damaged area before using silicone.

I might need a new socket. The wire broke off the connector that is in the socket and makes a connection with the pin on the CRT base. Likley I will need to get a new connector even if I could easily open the socket I made a crude drawing of the conector. The red line indicates where the connector broke. Thanks for all your help.

Ross

To save some time and effort, strip back some insulation on the broken wire and solder it next to the connector. If you are careful, try to cut back on that pink fiberglass disk behind the socket with a cutting tip of a dremel tool to get at the terminal. Changing the entire socket for 1 wire shouldnt be nessisary.

Update
 

I used silicone caulking on the flyback and I had problems with 4 wires on the socket. A friend and I used wire spades and a pop ricket gun to fix the socket. The focus 9 pin was very badly corroded in the socket. Now I have sound plus a raster but no video.

Ross

High voltage problem
 

Looks like I was wrong about not getting video. I attached my Sencore Dot Bar/Color Bar generator to the TV and got this picture. It is a bit out of focus and after a few minutes the left side of the picture shrinks a bit. Where might I need to check in the high voltage section of the tv? Thanks.

Ross

Sixties Motorola Color
 

Motorola introduced the 908-Y chassis in the fall of 1963. This chassis was an excellent performer, and used the rectangular 23EGP22 CRT, which was developed jointly by Motorola and National Video Corp (both in Chicago). This CRT was the world's first mass-produced rectangular color tube. The sets were deluxe models with Drexel cabinets, and were priced accordingly. About 100,000 of these sets were manufactured.

During this time Motorola also marketed a budget line of color sets using round CRTs & series-filament hot chassis in cheap cabinets. These were priced at about half the price of the rectangular models, and did not sell well. I was not aware that Motorola had produced a round tube model with a transformer-powered chassis in the sixties - must be quite rare.

Today it is rare to find ANY Motorola color set, including the Quasar! In the sixties, they were common. :confused:

Tube Layout
 

Here is the tube layout for you guys there are curious about my set.

Ross

picture looks a bit washed out. Did you try adjusting your AGC control? If you did and it didnt help darken up the picture, test your IF tubes and that 6HS8 AGC/clipper. Should that not be the case, then check your video amplifier tubes. you should have probably 25KV on the the anode if HV is properly set. To check the HV, turn the brightness and contrast all the way down, then try to stick the HV probe between the anode cap and the CRT well and adjust your HV for about 25 KV. Your focus voltage should read at 5KV. Poor/ corroded connection to the pin of the crt can cause the focus to go off. But if you want, touch your HV probe on the focus lead (probably black) and see if youve got 5KV, if so its a connection problem most likely.


Just as a safe rule I follow, when I get a TV for the first time that I work on, I test every tube in the set, even though the set might appear to work ok. Sometimes the set is working good but the grid leakage is poor, or a life test on a tube fails indicating trouble is on the way. Its just a good habit to get into I think, it also makes you feel good as you now know ALL the tubes are good, and you feel more confident in relying on the TV to work good.

keep us posted.

Update 1/26/04
 

I have had to replace R145 a 100K resistor that was split into two that went to the focus control. I used my high voltage probe and only got 4KV off the focus rectifer. Also I had to replace C2 a 2Mf 350 Volt Electrolytic that is in the vertical section. Now I am only getting the picture showed my prior posts briefly because the picture fades to nothing after it is on a few minutes. The only voltage reading that I did take in the high voltage section that seems to be very low is on Pin 5 of the 6BK4. It should read 360 Volts and I am only getting 230 Volts. Anyone have any ideas where I should try and why I am losing high voltage? Thanks for any help.

Ross

There is usually a 1000 ohm resistor in the cathode of the 6BK4, measure the voltage drop across the resistor. Voltage drop should be around .8-.9 volts corresponding to a current of 800-900 microamperes. If there is much more than this the 6BK4 is probably drawing too much current.

Too much 6BK4 current will drag the HV down. Have you traced the voltages back through the 6BK4 grid/cathode circuit to a place where they are normal? I have seen several cases where resistors changed value in this circuit and caused problems.

It sounds like a thermal problem since the HV goes down as it warms up...try spraying freeze spray on the resistors in the 6Bk4 circuit.

Also just to rule out tubes have you tried a new 6BK4 and HV rectifier?

And, keep in mind that problems in the horizontal output tube/damper circuit can cause low HV as well. Measure the screen and grid (not plate) voltages on the HO tube too.

Update 1/29/04
 

Tonight I measured the voltage on the 6BL8 Horizontal Oscillator/Horizontal AFC. Pin 1 should read .5V and it reads 2.5V and pin 9 should be -15V but I get -27.5V. The rest of the voltages appeared to be fine. Also I noticed that the 6GK6 audio output was not even light. After I resoldering some connections thinking it was a cold solder joint problem on audio output tube I plugged in the TV. I got a rush of static in the sound and then the TV started smoking and I had to unsolder a shield by the 6BL8 Sound Detector/Limiter to look for the part that caused the smoke. Visually so far I do not see what was smoking. Thanks for any help.

Ross

Ross, it sounds like there may not be enough drive signal from the horizontal oscillator...check the negative grid voltage on the horizontal OUTPUT tube grids...if it is low, then there isn't enough drive.

Also could you identify the tube elements such as grid, cathode, etc. that you test rather than just the pin numbers...it makes it easier to give suggestions because it is hard to remember what pin goes to what element.

When you got smoke it was probably a resistor that burned...maybe a shorted capacitor in the circuit that connects to the resistor.

Part of schematic
 

Here is a partial schematic of the TV. Specially the high voltage section of the TV. I found the resister that burnt and replaced it. Thanks for any help.

Ross

High Voltage problem
 

I checked the high voltage tonight. After the voltage fluctuates between 2000-5000 volts a few times, it settles at 5000 volts. I am referring to the CRT voltage which should be be about 23,000 per the SAMs schematic. What might be causing such a voltage drop? I have subsituted all the tubes in the high voltage section. The picture I posted in earlier postings will only show for about 30 seconds. Thanks for any help.

Ross

Hello St. Louisian,
One thing you could try to eliminate the shunt regulator stage as a problem is lifting the cap off the top of the 6BK4. You will have to keep the plate cap away from anything as it will have HV on it. You could also connect your HV probe to the 6BK4 plate cap to lessen the possibility of arcing. If that doesn't make any difference try scoping the control grids of the HO tubes to make sure the sawtooth peak to peak voltage is what it should be. Let us know what happens.

Jeff (PUNK ROCK DUDE)

...

Update 3/29/04
 

How do I measured the P-P Pulse Voltage? Is this something I can measure with a VOM? The 660 Volt and 790 Volt Boost Voltage is low when I tested it. Thanks for help.

Ross

Could C522 or C523 be shorted or leaking to cause the voltage to be low on pin 5 of the 6BK4?

Thanks,

Ross