I have a 1974 Zenith Chromacolor II with Space Command remote that won't turn off unless it is unplugged. Even as soon as it is plugged in, it turns on. The vertical picture shows the wiring for the control panel. The blue wire all the way on the left connects to the power button (it is a push button on/off switch). I tested the switch, and found that it works. I disconnected the plug connected to the blue wire, and the set still wouldn't turn off. The power button on the remote only changes the channel. Any suggestions? I don't know where to start.

I bought the set with a broken step up transformer. I fixed the transformer and this is as far as I got. I don't think that the transformer has anything to do with the TV not turning off, but I could be wrong.

It's been a few years since I last worked on one of those, but IIRC you will find a shorted triac on a heat sink up on that tuner/remote assembly. Should have plastic covered blue, gray, or black wires going to it that are different from the cloth covered wires on most of the rest of that area. Those might be the ones I see running vertically near the bottom of the closeup photo of the tuner/remote section.

Most likely the set got hit by a power surge or there was a lightning strike in the area but not a direct hit. This wasn't a high failure part, but about the only thing other than a short in the wiring which would cause the set to stay on all the time.

Get a genuine Zenith part, aftermarket replacements do not hold up well. Might have to get a used one, but there was someone in Classifieds selling new Zenith modules the other day for $1 each. If you can find the little subassembly with the triac on it in his list, that part might be able to be removed and installed into your set. IIRC there are several different versions of that triac subassembly that were used over the years.

Or, you can just repair it the way a lot of antique radios are repaired: drill a hole in the side and install a toggle switch.

Dennis is right; I remember that problem from the "old days". As I recall, the replacement triac came with a MOV which was supposed to protect the new one from power surges.

The complete assembly might be available from one of us with old Zenith parts in stock; look for a part number starting in "A" or "S".

Mr. Detrola,

Thanks very much for posting. I am far from an expert when it comes to electronics. If I could find the part, there should be no problem installing it, but I am not sure which part you are talking about. It is very likely that a power surge damaged the part. I remember the first day I plugged it in, the transformer started smoking (now its replaced). Also, the space command remote doesn't work very good. I know these remotes never worked well from day one, but the power button makes the channel go down, and the channel down button doesn't work at all. Could the power problem and this problem be related?

You said there is a "shorted triac on a heat sink." Could you describe what this is, or describe what part I need. I would appreciate it.

I think I found the shorted triac, but someone correct me if I am wrong. It may be the small blue box with three terminals (see pictures). I used a VOM meter, and found that there is no resistance between the first and third terminals, but there is a little resistance in the second terminal. I don't know if that helps. There was an old repair job near the triac. Also, both of the blue wires that attach to the power button are grounded to the chassis. I don't think there is supposed to be continuity between these wires. Is there anyway that I can confirm that the triac is shorted? If so, does anyone have a replacement? The traic reads "185-9 GE 7334."

That sure looks like it! 185-9 crosses over to an ECG 5635, which is a 10 amp 400 volt triac. When you say "no resistance", are you reading a dead short or an open circuit?

As for the wiring, a schematic will be a big help at this point. Post the model number; one of us may have the original Zenith manual, or a Sams folder for your set.

Tim Tress,

Thank you for posting. Where did you get "ECG 5635" and "10 amp 400 volt" from? If I need a part, do I ask for a 10 amp 400 volt triac?

I am not sure of the difference between "short circuit" and "open circuit." I disconnected the assembly shown in the picture and tested it with an ohm meter with no external power going to it. Most of the time, the gauge went all the way to the right, indicating continuity. When I tested the continuity of the middle terminal, the needle almost made it to the top, but not quite. Everything described that I tested, I tested without any power going to it. Sorry if this was confusing. I am still in the process of learning about electronics.

I cannot read schematics too well. Not sure what good it would do. Would a schematic show what part I need? I was thinking of simply cutting off the old triac and replacing it. Would this solve the problem? If this unit needs more work than that, I was thinking of taking the assembly to a repairman, but I am not sure if he needs the whole TV to work on it.

Thanks for your time. Hoping to hear back from you.

Open circuit means that the ohmmeter would read very high resistance...there is little or no continuity between the connections. The meter would read the same as, or similar to, just leaving the test leads on the meter unconnected. Short circuit means that the ohmmeter would read very low resistance...close to what you would read on the meter if you just touched the test leads together. Based on some of your comments about your electrical experience, you're probably best off taking the set to a repair shop if there is one near you that works on older sets.

Think I found the part number. S-97335. There is another number below that says "3434031." Take a look at my radio classified posting. viewtopic.php?f=15&t=190118

Think I found the part number. S-97335. There is another number below that says "3434031." Take a look at my radio classified posting. viewtopic.php?f=15&t=190118

I doubt any repairman would want to get involved in that old set, particulary since it's been already "messed with" by a tinkerer.

I agree that you'd have a hard time finding a TV shop who would work on that set because most of them don't want to work on anything over a few years old. Maybe someone on here who is close to your location will step in and help you get it going.

The chassis used in this set is among the best that Zenith ever built. I have the regular knob tuned version of that chassis and it needs a tripler and some hack attempted repair work corrected. The cabinet is a little banged up; but, I can't bring myself to toss it. Those had great pictures when working right and they will outlast this current Chinese junk.

I am in the south chicagoland area. If anybody is closeby who would like to look at it, feel free to let me know. I can either bring the tuner over, or you can come by and look at my television.

I am still debating on whether I should try replacing the TRIAC myself. Will simply replacing the small part solve the initial problem, or is there more to it that I don't know about?

They have already outlasted many chinese FP sets several times over considering that a good FP set these days is one that survives it's warenty period!

Odds are that in adition to the bad triac the Sapce Command reciever probably needs to be retuned. Some of what you describe on the remotes functioning (dead keys, a key opperating the wrong function, etc) makes it sound like it needs to be retuned(or maybe you have the wrong hand-unit?).

Retuning is simple look at the schematic for the Space Command chassis and tune the last adjustable coil(or transformer) before each relay while continously pressing the button for the coresponding relay on the remote (you can connect a volt meter or a scope to the relay coil and adjust for maximum voltage if you really want it to work great) until the relay begins to respond to the remote. I'd start on the coil for the relay that is not responding to the remote frst as it will allow you to get the hang of it and not worry about messing up what is already working. You will need a plastic hex alignment tool (like used for the convergence coils) to adjust the coils. I had to do this to a 63' Zenith SC set once and sam's had the adjustments for the different relays (two in my set) mixed up on the chassis diagram so I'd double check the wiring of the chassis before doing any adjustments if I were you.
Mine had one non-responsive relay and one responsive relay, and because sam's had an error I detuned the good adjustment by mistake and had to redo both which was actually kinda fun once I got over being irked from sam's messing me up.

Hope this helps!

Tom C.

Oh, one thing to check on. The power button switch you actually press to turn the set on and off.

Try disconnecting the switch. As I recall, we often had to change the switches as they would start conducting tiny amounts of current between the contacts. Usually just enough to randomly turn the TV on or off.

It could be yours is gone bad and holding it on. A long shot for sure, but its not difficult to disconnect the leads and try it.

-Steve

The power button is working. I disconnected and tested it. As for the remote, I don't have schematics, but I will try to find the tuning coil.

If your set has more than one remote button function then there will be more that one tuning coil (usually one per button function).

Space command remote receivers are are usually on a separate chassis from the TV electronics.
If there are other issues with the power supply (like that triac) then retuning the remote reciever will not likely help with the power supply issues (though should remedy other remote function issues).

Tom C.

I tried replacing the TRIAC but it didn't work. I couldn't solder it directly to the board, but it is making connections to all three terminals. Any other suggestions?