'79 Zenith 12" B&W (I let the smoke out)

[radiotvnut]

My flea market friend picked this up for me at a local thrift store. He knows I like these old sets and when he can get them cheap enough, he picks them up for me.

When I first tested it, I noticed that the CRT was very weak, the tuner was dirty, and the contrast knob was broken. So, I opened it up and slapped my B&K 470 CRT tester on the picture tube. Sure enough, it was very weak; but, responded fairly well to rejuvenation. I can't make it out very well; but, the EIA code on the CRT is either 377 or 577. I don't know what those codes are; but, I suspect the CRT was built by Clinton Displays. And, I'm sure this set was built in Taiwan.

Then, I connected the cable to the 75/300 ohm matching transformer. While I was ovserving the improved performance, I accidently moved the cable and the ground conductor, where it screws into the balum, touched the metal case of the tuner, which resulted in a loud BANG, some smoke, and a foul odor. So far, the only thing I've found wrong is that one of the RFI coils on the AC input is burnt to a crisp and measures open. I had to do other more pressing work; so, I didn't check any further. Hopefully, the AC input and power supply components will be the only thing damaged. If the whole set ends up being fried, I'll just have to scrap it.

Years ago, I've had a few of these solid state Zenith B&W's from the late '70's and they were good performers.

EDIT: It looks like the CRT was made by Chunghwa of Taiwan. I've seen that brand in many TV's, even later models.

[ChrisW6ATV]

I remember that BANG! sound well, when I first learned what a "hot chassis" was, on my 1979 Sony 19" color set. "Ground" is not ground!

In that set, I blew its fuse and one or more diodes in the power supply. After they were replaced, it worked fine until I sold it in 1982.

[radiotvnut]

I got it back on. To do so, I had to replace a shorted rectifier diode, a blown fuse, and the AC input RFI choke that was burnt to a crisp. Tomorrow, I'll feed a signal to it and I'll try not to let the cable short to the chassis.

There's even the usual Zenith warning printed on the back cover that was a carry-over from the tube era that states "The chassis of this receiver is directly connected to one side of the AC line".

And, yes, this set was made by Zenith of Taiwan.