'74 Zenith 25EC58 from SC is alive!

[radiotvnut]

I dug into the '74 25EC58 solid state horizontal chassis Zenith that I brought back from SC. The "no video" problem was caused by a blown CRT filament fuse. It now works; but, still has some issues that I need to correct. First, the picture is too bright and a little washed out. At present, I have the contrast control turned all the way up and the brightness control turned only approx. 1/4 of the way up. Second, the picture is jittery, espicially for the first minute or two. After it warms up, it looks better; but, any writing on the screen still has some jitters. And, it will need the usual control cleaning and touch ups. It still has those white safety caps in the HOT circuit; so, those will be replaced with orange drops before I'm done.

The cabinet is plastic and particleboard; but, the chassis is very well built. If I had a choice, I'd rather see a well built chassis inside of a cheap cabinet instead of a top quality cabinet that housed a junk chassis.

[ctc17]

COOL! I dont think mine has that oil filled ac cap. Ill have to look. What is that used for in this set? They use those with motors for power factor correction. Is it to help with power transformer power factor correction?

[radiotvnut]

I believe that's what it's used for. These sets, along with many others of the era, used a ferroresonant power transformer in combination with this oil filed cap as a means to regulate the B+ voltage.

[Eric H]

Originally Posted by radiotvnut

These sets, along with many others of the era, used a ferroresonant power transformer.

Is that the same thing as a SOLA transformer?
I know Dumont used those and that one looks similar with a tall profile.

[sampson159]

very simply-the best there was,the best there is and the best there ever will be!

[freakaftr8]

Kinda sounds like an AGC issue to me. Was Zenith still using the "buzz" pot on that chassis?

[radiotvnut]

I don't think there's a buzz control on this set. Tomorrow, I plan to start checking caps.

[radiotvnut]

I checked this TV some more and I think the problem may be in the brightness limiter circuit. I noticed that someone has already replaced the 220 ohm resistor that connects to the center terminal of the brightness limiter control. When turning the control, there is almost no change in the brightness until it's turned all the way down and there's not much more change, even at that. I'm going to check the resistors and a 7.5 volt zener diode that's in this circuit. When I measure voltage across the 7.5 volt zener diode, I get a reading of zero.

Once I get this problem solved, I'll work on the jittery picture.

[holmesuser01]

Didnt the buzz control go away when Zenith went to solid state? I'm having old-man brain farts today.

Great score in SC!!