drh4683
08-28-2006, 08:38 PM
This is the one that was on ebay in MI a couple weeks ago. I picked it up last friday. The TV turned out to be near mint with very few hours. The guy I bought it from bought his grandparents home with all the furnishings. This was a wealthy family and his grandfather co-owned a machining outfit. They had a large ranch home built in 1956 (which you can tell by the photos of the background, its still 1950's inside). The TV as well as everything else in the house was extremely well cared for. As for the TV, He said that his grandmother stopped watching it years ago for some reason and kept it unplugged since around 1977 or so.
That made me wonder why it was unplugged? As I plugged the set in, I noticed a terrible blue convergence problem on the left side along with a light green tinted left side of the raster. Didnt get to concerned over that.
I made it back fine as well as the TV. Dwight helped me load it up as I stopped by his place that day to give him a few sets.
I started working on the set saterday morning. I noticed that the left side blue horizontal lines convergence pot was toast. You could feel the windings come apart as I turned it. That meant pulling the convergence board out. I ended up having to take a known good control out of another set as I didnt have any good ones in my parts boards. Put it back together and still nothing, control had almost no effect. Pulled the board again and suspected a faulty convergence rectfier. Sure enough, one of the four sections had a dead short, for the left side blue convergence. I have a few NOS replacements so I popped in a new 212-72 and that did the trick. Converged perfect. The focus aligned razor sharp too. This explains why the set got unplugged. That shorted rectifier burned that convergence pot to a crisp. there were black flashing marks all around the control and on panel in the vicinity of the pot. So it must have smoked or made some kind of noise and freaked the lady out.
As for the rest of the set, the HV was too high, near 30KV. On this chassis, zenith soldered a blank off cover over the HV control so nobody would adjust it. No reason for this other than X-radiation laws etc. I turned it down to 25KV no problem with plenty of range on the control yet. Checked the HOT current and was running about 203-205 mA. Couldnt get it any lower than that. Besides, turning the efficiancy coil had a minimal effect on meter deflection durring the adjustment. Seems like alot of zeniths just dont respond to the efficiancy coil adjustments like they do in the RCA's. Also replaced a few tubes. The 6HA5 rf amp was almost dead. That brought the picture back strong. Remote control works fine with no repairs.
This set also came with the original paper work which I was not aware of. Since it has the ultramatic UHF tuner, it also came with the sheets for the channel number inserts for the UHF stations. So I was able to "chicagoize" the TV with chicagoland UHF channel numbers.
Turned out to be a very nice set. I dont have any 1970's space command consoles. Ive always liked the 12A12C52 chassis just by studying them in the schematics. Never had one untill now. FYI, the chassis itself is only 12 tubes with a handfull of transistors and one plug in dura-module. Anyone else worked on the 12A12C52? Seems like the biggest (lengthwise) chassis zenith ever put in a set next to the 25MC33. I also think 1970 is the first year zenith went to the rounded tube cap on the back cover.
As for the clean insides, thats all original! Only thing I did was dust off the tops of the tubes durring testing. Otherwise, I didnt touch a thing inside as far "de-dusting" goes. One of the cleanest no dust sets ive had.
That made me wonder why it was unplugged? As I plugged the set in, I noticed a terrible blue convergence problem on the left side along with a light green tinted left side of the raster. Didnt get to concerned over that.
I made it back fine as well as the TV. Dwight helped me load it up as I stopped by his place that day to give him a few sets.
I started working on the set saterday morning. I noticed that the left side blue horizontal lines convergence pot was toast. You could feel the windings come apart as I turned it. That meant pulling the convergence board out. I ended up having to take a known good control out of another set as I didnt have any good ones in my parts boards. Put it back together and still nothing, control had almost no effect. Pulled the board again and suspected a faulty convergence rectfier. Sure enough, one of the four sections had a dead short, for the left side blue convergence. I have a few NOS replacements so I popped in a new 212-72 and that did the trick. Converged perfect. The focus aligned razor sharp too. This explains why the set got unplugged. That shorted rectifier burned that convergence pot to a crisp. there were black flashing marks all around the control and on panel in the vicinity of the pot. So it must have smoked or made some kind of noise and freaked the lady out.
As for the rest of the set, the HV was too high, near 30KV. On this chassis, zenith soldered a blank off cover over the HV control so nobody would adjust it. No reason for this other than X-radiation laws etc. I turned it down to 25KV no problem with plenty of range on the control yet. Checked the HOT current and was running about 203-205 mA. Couldnt get it any lower than that. Besides, turning the efficiancy coil had a minimal effect on meter deflection durring the adjustment. Seems like alot of zeniths just dont respond to the efficiancy coil adjustments like they do in the RCA's. Also replaced a few tubes. The 6HA5 rf amp was almost dead. That brought the picture back strong. Remote control works fine with no repairs.
This set also came with the original paper work which I was not aware of. Since it has the ultramatic UHF tuner, it also came with the sheets for the channel number inserts for the UHF stations. So I was able to "chicagoize" the TV with chicagoland UHF channel numbers.
Turned out to be a very nice set. I dont have any 1970's space command consoles. Ive always liked the 12A12C52 chassis just by studying them in the schematics. Never had one untill now. FYI, the chassis itself is only 12 tubes with a handfull of transistors and one plug in dura-module. Anyone else worked on the 12A12C52? Seems like the biggest (lengthwise) chassis zenith ever put in a set next to the 25MC33. I also think 1970 is the first year zenith went to the rounded tube cap on the back cover.
As for the clean insides, thats all original! Only thing I did was dust off the tops of the tubes durring testing. Otherwise, I didnt touch a thing inside as far "de-dusting" goes. One of the cleanest no dust sets ive had.