Sony KV-1710 horizontal osc

[andy]

I just picked up one of these early 70's sony color TVs for $0.49 at goodwill. I normally wouldn't bother with something like this, but it was cheap, in excellent condition and I had one as a kid that I bought from a yard sale and tried to fix(Had a bad CRT, storng green, red and blue totally dead). The CRTs in these old sonys always seemed to lose the red and blue way before the green for some reason.

I do have the service manaul, but I'm still having trouble figuring out the horizontal osc circut on this set. It seems to be a very unique design. Basically, the set is dead, no HV. B+ is getting to the HOTs (2 in parallel), but there is no drive. The osc circuit doesn't seem to be getting power (the +12v to the osc is measuring around 2v). Sounds easy, but the +12v supply comes from the flyback. I don't see any startup circuit, or circuit to provide temporary power to the osc. Before I spend any more time on a set that almost certainly has a bad CRT, does anyone have any experience with this vintage of Sony TV?

[kc8adu]

i believe that one divides off main b+ to leak a startup voltage.
just enough to make it run somewhat till +12 comes up from the fly.
maybe the osc ic or whatever is loading it down?
been a while since i worked on one of those.
at least you dont have the sg-613 eater model.
sonys of that era had resistors that would have the coating crumbling off. some were fine and some would be way off.

[andy]

Thanks for the tip. That makes sense because the 2v I'm measuring has to be coming from somewhere. I'm thinking either a leaky transistor, or increased value resistor. It uses no ICs in the horizontal osc circuit.

[jwr1057a]

I'm new to this site, you're my 1st reply!
If you still need repair help on that old Sony, I know what it is.
The "start-up" circuit on that chassis is complicated; 1 'lytic capacitor!
Your testing the old memory and it ain't what it use to be!
Here goes; the capacitor is a 10uF @ 160V or 250V on the PC Board directly under the CRT. Look at the schematic, it connects from raw B+ thru a resistor to the "+" side of the cap, the "--" side connects to the horiz osc B+ line. I think that was 12 or 18V. Totally simple, only 2 parts! Other makes used over a dozen parts to do the same thing!
It operates like this; when the set is 1st turned on, the raw B+ (150V I think) ramps up and the cap charges thru the resistor to the horiz osc B+ line. Since the cap is like a short circuit when not charged, that raw B+ is dumped thru the current limit resistor to bring up the horiz osc B+ close to normal. The horiz output circuit drives the HOT and the scan derived 18V supply takes over. The start-up cap charges and no current flows from it and the resistor anymore. Walla! Simple and effective!
I bought a KV-1710 from a Sony Dealer I worked at in 1974. We sold and serviced also. That's where I "fell-in-love" with Sony. My little Sister still uses that set in her Daughters' room to play games, etc. The set still looks brand new after 33 yrs. Instant on kept the CRT alive all these years!
Remember, 2 yrs later in '76, no more instant on! That TV won Sony an Emmy, the 1st time a TV got one! That was the most popular set of all times! It was on many commercials, TV episodes, talk shows. etc. That set was the 1st TV to make water look like water!
Anyway I'm rambling! Have fun and Happy Holidays... John

[andy]

Wow, that was a few years ago. I didn't even remember the set until I re-read my original post, but I think it did end up being a bad cap.