Sony KV-1204A: Where to start?

[ESigma25]

I managed to liberate a Sony Trinitron KV-1204A (12 inch portable set from 1977) but it doesn't power on at all. Pull the power switch and get...silence.

I'm not familiar with these at all so I gotta wonder, where should I start? I would assume there's a fuse on the analog board that would be a good place to begin, but what else can I check?

[Popester]

Some of these early sets came with a circuit breaker. It’s all going to depend what kind of test equipment you have. Do you have a way to test the emission on the crt? If crt is weak trinitrons can’t really be rejuvenated. A DVM could test rectifier circuitry in the power supply. Sony’s are a unique animal so a manual is really the first thing you’ll need to start with. KV-1204 would be early ‘70’s product. Good luck.

[ESigma25]

Originally Posted by Popester

Some of these early sets came with a circuit breaker. It’s all going to depend what kind of test equipment you have. Do you have a way to test the emission on the crt? If crt is weak trinitrons can’t really be rejuvenated. A DVM could test rectifier circuitry in the power supply. Sony’s are a unique animal so a manual is really the first thing you’ll need to start with. KV-1204 would be early ‘70’s product. Good luck.

I don't have any CRT test equipment but I can't even think of testing the tube when the set doesn't respond at all to the power switch.

[Popester]

A DVM could tell you if the on/off switch has continuity or not. The earlier point I was trying to make is if the crt is really weak or dead as far as emission goes, than fixing it to get it to power back up might not be worth your time and effort. Is a KV-1204A really from ‘77? I thought it would be earlier like ‘72 or ‘74. Regardless a manual will be needed and maybe someone here on the forum would sell you one or you could buy a downloadable file copy.

[Popester]

A lot of Sony sets used a derived power source that came off the flyback transformer. So the horizontal circuitry had to be running so the flyback could supply the other power sources that ran other things in the circuitry. Be very careful with the anode connection in these as it is coaxial. As I stated earlier these were very unique in their design. Not like the typical American made sets of the same time. Very reliable products. CRT’s tended to have a shorter lifespan but that was probably due to a brighter picture/contrast compared to a shadow mask type of CRT.

[ESigma25]

Originally Posted by Popester

A DVM could tell you if the on/off switch has continuity or not. The earlier point I was trying to make is if the crt is really weak or dead as far as emission goes, than fixing it to get it to power back up might not be worth your time and effort. Is a KV-1204A really from ‘77? I thought it would be earlier like ‘72 or ‘74. Regardless a manual will be needed and maybe someone here on the forum would sell you one or you could buy a downloadable file copy.

All the websites I was looking at said 1977 but it's probably an earlier model than that.

[Popester]

After typing in a Google search it does look like this is from '77 or '78 model year. Not sure if this used the SG613 HOT switch but they would short and take out a bunch of components. Check the HOT for a direct short, the damper diode, for a short, look for an inline fuse with a hard blow failure. HOT is usually mounted on a big heat sink and the damper diode will be near by maybe even soldered to the back of the transistor. I was thinking this was a earlier model, but they're numbering scheme didn't always make sense to me. I don't know if this has the SG613 or not but they were in the '75 model KV-1920, and KV-1722 sets. Not sure about the smaller ones. If the jug is good, it would be worthfixing as they are excellent sets and were so reliable. These sets used a HV block that was similar to a Zenith tripler. The casing could crack and arc to ground. I fixed one arcing to ground with epoxy glue and it's still working. That was on a KV-5200. It's hard to beat a Sony but they can be a bear to fix. Good luck and update as you get things going again.

[zeno]

This is an SG613 set, actually SG264 that IIRC subs to an SG613.
If the SG is shorted I would STRONGLY suggest not trying to fix it.
The regulator transistor & fuse are blown with it along with a few resistors.
Trouble is something else caused it almost always. If you dont find the cause
it will blow again right away or sometimes run perfect a while then blow.
In the day almost no shop would fix one. The ones that did charged flat rate $120 - $140 about double the usual rate. That was real $$ back then, see the price of cars !

73 Zeno
LFOD !

[ESigma25]

Alright, if it is shorted I'll just hold onto it for parts or pass it on to one of you guys. The set is in really good shape aside from the whole not working thing and all the knobs seem to be intact, though one of the long narrow black knobs (the color fine tuning ones) doesn't seem to fit on right.

[Popester]

You never know until you check some things out. SG613 sets were hard to fix, but not impossible. I'd dig out a DVM or VTVM before you pass judgement and let it become a parts set. Certainly worth investigating into it. My recommendation would be to use all OEM parts for the damper diode, HOT SG613, and not use equivalent. Our shop tried using equilavent parts for the SG613 and damper diode and sure enough the issue would show up again,but OEM parts worked and lasted better. This design didn't last thankfully all that long and us technicians were very grateful for that. Zeno and I aren't trying to frighten you out of repairing the set, but want to educate you about issues you could run into. Check the easy stuff first. Is the power cord check good with continuity? The on/off switch could be open. Look for bad solder joints. Take the back off and just give a real close visual look for discolored resistors, cracked solder joints, blown fuse, electrolytic caps with bulged top or electrolyte leaking out the bottom of the cap, or stuff like that. Maybe you have something real easy to fix. Good luck and keep us posted. Can you at least post a couples pictures of it?

[freakaftr8]

True. Also my KV3000R was dead and had a shorted horizontal output transistor. Some cracked solder connectors. Replaced the HOT, repaired solder problems and pioped in a new fuse back in 2010. Still running strong. Dont be afraid to test things.

[ESigma25]

Originally Posted by Popester

Can you at least post a couples pictures of it?

Sure, here you go. It's a touch grimy but it's in really good shape which is why I'm attempting to resurrect it.

https://i.imgur.com/QewfEMk.jpg

https://i.imgur.com/3KMazQY.jpg

https://i.imgur.com/0Zvia8w.jpg

https://i.imgur.com/tmMwUe3.jpg

[Popester]

Grimy, where? That set looks pristine to me. I see your problem. It's got no power cord hence why it's dead lol😂. One very important thing to mention is that if you get down to troubleshooting with a scope or VTVM you want the power of the tv plugged into an isolation transformer. Not sure these are transformerless for the power. All servicing of modern tv's or old ones, radios tube or SS an isolation transformer is a must to protect you and the vital test equipment you might have against dangerous shock. Thanks for the photos please continue with the troubleshooting.

[ESigma25]

Originally Posted by Popester

Grimy, where? That set looks pristine to me. I see your problem. It's got no power cord hence why it's dead lol��. One very important thing to mention is that if you get down to troubleshooting with a scope or VTVM you want the power of the tv plugged into an isolation transformer. Not sure these are transformerless for the power. All servicing of modern tv's or old ones, radios tube or SS an isolation transformer is a must to protect you and the vital test equipment you might have against dangerous shock. Thanks for the photos please continue with the troubleshooting.

The back shell has some stuck-on dirt that I haven't gotten off yet.

As for the power cord, it's just kinda...flung to the side so that I'd be able to wipe down the back, you can sorta see it in the second photo. I keep it wrapped up on the back most of the time.

[Popester]

ESiigma25, you have any update yet from this set yet?