#16
|
|||
|
|||
...
Last edited by andy; 11-18-2021 at 04:57 PM. |
#17
|
||||
|
||||
Quote:
Hitachi, Panasonic using it. The Zenith CC2 & flat chassii had NO HVSD circuits. The dept of HEW approved both the S caps in parallel & the 4 lead caps for X-ray protection. Most mfg's both US & Jap in the mid 70's on their top of line sets copied the Zenith fero-resonance supply & cap arrangement some without HVSD. Looking back Zenith & Maggy regret not having HVSD 73 Zeno LFOD ! |
#18
|
||||
|
||||
Quote:
|
#19
|
|||
|
|||
Look for a bad 20-30 volt zener in the "x-ray protect" circut.
|
#20
|
||||
|
||||
Quote:
up its either too much HV or a fail in the HVSD. The ones I remember were the 19" delta tube sets. A shorted pass transistor was almost always the culprit. This chassis IIRC was only in 19" & didnt use SCR's. Twas my favorite 1970's RCA. BTW Maggy can be added to the list. IIRC it was the ones with the 703744-## PS boards. Didnt stop them from cutting the neck off CRT's. Since Zenith sold 20%-25% of sets then they took all the blame.Maggy had the horz shift & a 4 lead cap to prevent catastrophic failure. Didnt always work. 73 Zeno LFOD ! |
Audiokarma |
#21
|
||||
|
||||
Quote:
Quote:
Oh, and on the subject of snowy pictures: this set had that problem as well and the AGC control had little effect. Then I found the RF bias control on the AGC/sync board and adjusted that slightly; presto, no more snow. Get off my screen and onto the ground, thank you. Back to our regularly scheduled programming. Last edited by Jon A.; 05-21-2018 at 09:02 AM. |
#22
|
||||
|
||||
RF bias is RF AGC. Changes the voltage to the RF amp
at the base or gate if its a FET. Usually turn til the snow just goes away. Too much causes jitters. IF AGC controls are rare in SS sets. IIRC the first Zenith flat chassis ( C-line) had both. You can home brew a great DGS coil but I dont remember how many turns of wire so check the internet & old books. Just be SURE to use a spring loaded on/off switch. It will brew up if you forget to turn it off. 73 Zeno LFOD ! |
#23
|
||||
|
||||
It's an odd setup for sure, an RF bias control on the AGC/sync board and another control simply marked "AGC" on the preset tuning board.
I looked into the home brew coils but chances are the magnet wire would cost as much or more than a ready-made coil. I've already called one for my B-day in a few weeks so problem solved. |
Thread Tools | |
Display Modes | |
|
|