1965 Zenith Chassis 25MC36Z
 

I bought a 1965 Zenith color TV console yesterday, model 8642-6 and chassis 25MC36Z. I really haven't looked over the tubes closely, but the more immediate problem is that the filaments in the neck of the CRT aren't lighting up. The audio works fine, and when I attached a Sencore CR161 to the CRT the emissions show weak for the red gun, but strong for the green and blue. The filaments light up when the tester is attached. I plan to try to get a hold of the schematic for the set, but was wondering whether anyone might have some idea what would cause the problem. Would a bad tube impede power to the CRT? I did reach back and touched something I shouldn't have and got quite a jolt, so I think the high voltage is working okay.

Follow the brown filament wires back to the chassis. You might have a poor solder connection. It’s also not out of the realm of possibility that the crt cabling connector could be bad. Zenith also used a rectangular fuse called a bell fuse. But I can’t remember if one was used for the filament voltage line or not.

I believe Zenith used fusible links (thin magnet wire) for heater lines as did everyone else.

I dont have the manual BUT this is how its probably wired.
The twisted pair of brown wires to the CRT are the filament.
They probably go to a separate winding of the power transformer.
There will be a fusible link in series. I have never seen one go except
when they are the line fuse. The filament is above ground & usually
"rides" on abt 150VDC to keep it near the cathode voltage.

1) carefully remove the socket. On old sets with bakelite on the CRT end
hold that & rock it off. If stuck slowly pry with a little screw driver.
2) measure the 2 filament pins for 6.3 VAC. If the 6.3 VAC is there its the
CRT socket or CRT. If not there its down on the chassis.
3) common problem is the CRT gets gets cold joints where the CRT wires
come into the pins. Resolder them but only the filament ones for now.
They go intermintant & cause the pix to fade in & out.

Last thing is the weak red. Rejuve is a last ditch cure. Get it running
right first. Testers are not perfect. I have seen nearly dead guns look
good & strong ones bad.

73 Zeno:smoke:
LFOD !

Thanks, Popester and Zeno. It did turn out to be a loose connection in one of the brown wires. I just pushed it in a little further and the picture came on. The color and sharpness of the picture looks great, at least by old TV standards. There doesn't seem to be a problem with a lack of red. It's got a 25BAP22 CRT which might be a replacement. I've seen ads for them from the early to mid-1970's.

Yeah, it happens, the insides of TVs are guarded by some really strange creatures that don't take very kindly to hand intrusions .... :D

Just doing a little troubleshooting.