Please Help ID Space Command Parts.. - Videokarma.org TV - Video

Tubejunke · #1 10-04-2009, 12:26 AM

The pictures below are taken from a 1958 Zenith Space Command with a chassis marked 18C24Q. The parts I am trying to ID are contained in the coil can designated T4 in a schematic I have of similar models. The first picture shows the part that I found to be open. According to my reading of the schematic it is indeed a coil. It is marked either L5 or L6 on the schematic. I am fairly certain it is L5 which is shown running into a diode symbol. L5 has no value but L6 shows 1 ohm.

Long story short I am trying to identify the components in both pictures. The supposed coil in the first shot looks like it is made of, or encased in some kind of black gelatin and bears a green dot which I guess signifies its value.

The second picture is viewed from the top of the chassis with the can removed from T4. At 11 o-clock I see what looks like a short, light colored resistor with three color bands, and over to the right is a very small component that is a little smaller than a 1/4 watt resistor and looks as if it is clear, with color bands. Is this a diode? In the schematic there is a diode symbol designated as X1. Is the tan thing a capacitor? The schematic shows two capacitors (C17 and C18). There is a disc capacitor at 7 o-clock. I do know that at least.

I have been harping about this set for a few years here, all the way from trying to get it to work after being stumped following a recap, to trying to give the damn thing away. I can't believe the absolutely nobody wanted this clean, early remote set, with a strong 24" crt. The set is so nice I don't have the heart to do anything but give the repair another chance as the set would be a great daily user if I could ever figure it out.

For the record it has/had the same symptoms with both the old and new caps and some new resistors. Little or no vertical sweep, volume adjustable hum, and no reception. It kills me to have a real nice set with what is supposed to be one of the best performing chassis ever made and I have no luck after a recap. Anyone would at least expect SOME kind of improvement I think. Any help here will be great if there are any Zenith fans in this crowd.

Thanks!!

leadlike · #2 10-04-2009, 05:52 AM

The clear item is indeed a diode-the point contact germanium types I use in crystal radios typically look like this.

The tan item is a choke. You can find a color code chart on this page:

http://www.electronics-tutorials.com/basics/chokes.htm

This could be L5 or L6 that you are seeing on the schematic, hopefully this will clarify which one is which.

Findm-Keepm · #3 10-04-2009, 08:06 PM

Quote:

Originally Posted by Tubejunke

The second picture is viewed from the top of the chassis with the can removed from T4. At 11 o-clock I see what looks like a short, light colored resistor with three color bands, and over to the right is a very small component that is a little smaller than a 1/4 watt resistor and looks as if it is clear, with color bands. Is this a diode? In the schematic there is a diode symbol designated as X1. Is the tan thing a capacitor?

I

Yes, and Yes. The clear glass component with bands is a diode - Zenith part number will start with a "103-"

The tan component is a tubular ceramic capacitor, most likely a zero drift/temp compensated type. These rarely fail.

The coil/cap/diode combination is usually in the video detector - probably not a starting point for the symptoms you describe. I'll pull the Sams tomorrow afternoon (EDT) and see if I have anything to add.

Cheers,

Findm-Keepm · #4 10-04-2009, 08:12 PM

Have you checked the B+ circuits in the set? An open input filter capacitor would yield low B+ and the symptoms (Low/No Vert sweep, 120Hz hum in audio) you describe would be the result. The input filter cap is going to be a two or more section can capacitor, usually rated at more than 350V.

I'd start by measuring the B+ feed to the vertical circuit, and trace it back to the power supply if it is low.

Cheers,

Tubejunke · #5 10-04-2009, 08:51 PM

Quote:

Originally Posted by Findm-Keepm

Have you checked the B+ circuits in the set? An open input filter capacitor would yield low B+ and the symptoms (Low/No Vert sweep, 120Hz hum in audio) you describe would be the result. The input filter cap is going to be a two or more section can capacitor, usually rated at more than 350V.

I'd start by measuring the B+ feed to the vertical circuit, and trace it back to the power supply if it is low.

Cheers,

No, I have not checked the B+. With the set recapped and strong sound (hum) and high voltage, I (stupidly perhaps) took for granted that all of that was OK. Again, the set performs exactly the way it did coming through the door, with all new caps. I do understand that new parts are no guarantee that everything will perform as expected. Whatever the problem is, it existed when purchased, and continues to exist, regardless of new caps and several new resistors.

The reason I ended up in the video section is that I was combing all of the circuitry looking for misconnections, solder splash, checking resistors again, the whole routine. That is when I found that the black item in the first picture bearing a green dot was open. Still nobody has said what it is. I feel like it is the L5 or L6 coil. No matter what it is I know that it should have some measurable resistance (not open). This will probably be more of an issue once I get the big issues tackled.

This may sound stupid, but they say that there is no such thing as a stupid question. What is a good method of checking voltages on a chassis that has been disconnected from the tuner, speakers, and CRT. First, I fear that something could be damaged operating a chassis like this. It could be dangerous to ME if I don't disable the HV, or at least more dangerous. This all leads to my second fear that any measurements taken might be off with so many things disconnected. I already know that they made a universal test CRT that can still be found. Right now, I don't have this, as I'm sure many of us don't, but we still must check voltages. I know I could remove that large CRT and rig up a bench mount of some sort, including the tuner and speakers. That sounds pretty far fetched to perform a fairly simple procedure. Any ideas or advice would be great.

I love the sets from the 50s that the chassis is removed complete, with the CRT.