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 Post subject: HELP! TV Repair Noob :D
PostPosted: Oct Wed 25, 2017 2:40 pm 
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Howdy Guys,

Over the years, I've collected a bunch of TV sets that my Mom, Sister, and GF's have fried by not unplugging electronics when a thunderstorm is in the vicinity of their homes. Fortunately, they all seem to be showing the exact same problem, which is a bright horizontal bar at the center of their displays.

I'm guessing that their vertical amplifiers were taken out? That is, for some reason, the electrolytics and other components in that section could no longer survive the line surges that were being thrown their way over the years and finally gave up the ghost (shrug). Hey, I did try to warn them to unplug ALL electronics when a storm was around, but they never listened.

Anywho, what has me baffled is that 3 different sets from 3 different manufacturers are showing the exact same problem, which is no vertical deflection and a solid horizontal bar mid screen. Why all 3 sets would fail in the same way is beyond me, but I guess there is some reason this is happening that I'm not aware of, unfortunately. I'm going to throw one of them up on the bench, and I'm hoping you guys can give me a place to start checking voltages that might save me a bit of time. Since these are older CRT sets, I'm hoping that I might be able to find schematics online. I'm not really looking forward to spending $22.00 for a Sams on the things. I'd be willing to do so if I could fix all 3 sets and sell two of them, but we all know old CRT sets aren't going to sell, and even if they would sell, I'd never even come close to getting the money back that I invested in the things.

With all of that in mind, I'm not too sure how I should proceed. Should I fix them and put them in queue, lining them up for my Mom, just waiting for her to fry another one, or just say to hell with it, strip them all for parts, and just go out and purchase a 40" OLED for $250.00 and call it a day :D. Any help here would be appreciated!

73, Randy AB5NI

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Wed 25, 2017 4:36 pm 
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How about some more information, are these tube sets or solid state, how old are they? Solid state can be more prone to voltage surges. With more info and some pictures, someone here or on Video-Karma may be interested in taking them off your hands, what you might get for them is hard to say at this point. I would not recommend that you part these out. No two ways about it it would take money for you to fix them.

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Wed 25, 2017 5:28 pm 
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Location: New Hampshire
If they are solid state sets they should be easy & cheap to fix.
Best pick one out & post the make, model & chassis numbers. Also
a good chassis pix. Then we can help.

73 Zeno 8)
LFOD !


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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Wed 25, 2017 6:03 pm 
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Howdy Guys, and thanks for the replies :D.

Okay. Let me get all my ducks in a row. I'll write down all of the model numbers and take some pics. Then I'll let you guys tell me which one I should dive into and repair.
Be back in a bit...

73, Randy AB5NI

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Wed 25, 2017 6:27 pm 
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Hi Folks,

Okay. The first TV is a Sanyo, Model #: DS27590-03.

The Next TV is a JVC, Model #: AV-27715

There is another 19" or so TV, but I think I'd like to get one of these 27" going so my Mom can watch one instead of the 13" she can barely see :(. I was going to take some pics of the sets, but they are available via web search.

73, Randy AB5NI

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Wed 25, 2017 7:24 pm 
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ab5ni wrote:
no vertical deflection and a solid horizontal bar mid screen. Why all 3 sets would fail in the same way is beyond me
The bright horizontal bar is a very common failure mode with old TVs, often caused by normal age-related degradation of electrolytic or paper (or plastic-coated paper) caps in the vertical circuits. Whether the problem is caused by component aging or power surges, the fix is the same. Start with electrolytic & paper caps in that sweep section and go on from there.

Phil Nelson
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https://antiqueradio.org/index.html


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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Wed 25, 2017 7:53 pm 
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So these sets are not exactly vintage. I'm not so sure solid state sets are easier to fix. Later model sets grouped many functions into custom ICs that are hard to find replacements for sometimes.
The power supplies are based on switcher technology using the horizontal drive circuits.

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Wed 25, 2017 8:00 pm 
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If you just want to get your Mom a bigger set there are tons of 20-36 inch CRTs being dumped for free or for very little money.

Around here the Goodwill has good working sets for less than $20.


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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Wed 25, 2017 9:06 pm 
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Howdy Phil,

philsoldradios wrote:
ab5ni wrote:
no vertical deflection and a solid horizontal bar mid screen. Why all 3 sets would fail in the same way is beyond me
The bright horizontal bar is a very common failure mode with old TVs, often caused by normal age-related degradation of electrolytic or paper (or plastic-coated paper) caps in the vertical circuits. Whether the problem is caused by component aging or power surges, the fix is the same. Start with electrolytic & paper caps in that sweep section and go on from there.


Sounds like a winner, Phil. I think I'm going to fix the JVC. I've never worked on a piece of JVC gear before, and I'm really curious to see how they're built.

73, Randy AB5NI

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Wed 25, 2017 9:10 pm 
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Hey Tim,

Notimetolooz wrote:
So these sets are not exactly vintage. I'm not so sure solid state sets are easier to fix. Later model sets grouped many functions into custom ICs that are hard to find replacements for sometimes. The power supplies are based on switcher technology using the horizontal drive circuits.


I'd guess that they were made somewhere in the early 2000's or so? I'm hoping I don't run into any unobtanium. Should I run into some, I'll strip the thing for parts and call it a day.

73, Randy AB5NI

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Wed 25, 2017 9:14 pm 
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Howdy Eric,

Eric H wrote:
If you just want to get your Mom a bigger set there are tons of 20-36 inch CRTs being dumped for free or for very little money.
Around here the Goodwill has good working sets for less than $20.


You're right, Eric. I should make a stop by all the locations we have here in town, for sure. I still want to see if I can get one of these sets going as a backup for her, though.

73, Randy AB5NI

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Wed 25, 2017 11:44 pm 
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You might get lucky and there is only a fuse blown or something. I don't think you will be able to do much without a service manual. What's to prevent a new set from getting zapped?

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Thu 26, 2017 1:16 am 
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Hey Tim,

Notimetolooz wrote:
You might get lucky and there is only a fuse blown or something. I don't think you will be able to do much without a service manual.


Let's hope that I can find the service manual online for free and fix the thing. The instant I have to fork money over for a service manual is the same instant I strip the thing for parts. No use spending more money than the thing is worth to fix it.

Quote:
What's to prevent a new set from getting zapped?


Her living with me now, and I won't allow that stuff to happen :D.

73, Randy AB5NI

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Thu 26, 2017 2:05 am 
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Although it might seem the other way around, you are much more likely to find free info on the old stuff rather the new stuff. The copyrights expire after a while for one thing. Also since fewer people think of repairing the vintage stuff the info is in less demand, so lower priced many times.
I kind of doubt there is much that would be of any use to anyone, unless they were trying to fix a similar TV. In principle the CRTs might be in demand one day, but won't fit anything vintage. I have heard that if you want to save the CRT you should leave the yoke and such in place because they are kind of made for one another.

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Thu 26, 2017 2:06 am 
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With that JVC, bad solder joints on the Vertical Output IC (likely a TA8432K or similar chip)may be the only problem - we saw lots of them. Nice 24.50 labor-only repair back in the 2000s. If not, then just the IC. Some had a zener in the supply feeding the vertical that would short, killing the vertical supply. D422, IIRC - and troubleshooting is simple. Remove the zener, and deflection returns, well, that zener was bad. Just a hold-down function.

The Sanyo is probably a combination of a failed LA78_ _ IC, (likely a LA7838) and the pump up/boost cap in the vertical circuit. Easy peasy repair.

EDIT: Edit, and cheat-sheet: No need for a full set schematic - download the datasheet for the vertical chip - there is often a representative circuit that CLOSELY matches the circuit in the set - all the values of external components. Caveat on the LA7838 - the pump-up cap value on the datasheet is for a 14" display, and will likely be a larger value (220uf, IIRC) in that Sanyo.

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Thu 26, 2017 4:33 am 
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Thanks for all the great feedback, guys! I'm going to get a kid over here tomorrow to help me get the JVC up on my bench. I'll take the cover off, bleed the CRT anode a few times, and see if I can slide the thing out of the case without too much difficulty. I'll also clean the interior up and see if I can take a couple of pictures as well.

Thanks for that great info, Findm! I'm sure that will come in very handy. I'll make a few measurements and let you guys know what I find as well.

73, Randy AB5NI

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Thu 26, 2017 1:22 pm 
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Location: New Hampshire
I second Findm's opinion !

JVC was almost always always a cold joint under vert IC. Same with
Panasanic, Sony & Zenith. Its the first thing to check on ANY set with a vert IC.
In fact we always checked it even if something else was done.
Look for apx 1" long IC on a heat sink with about 7 pins. Dont confuse with
the audio out IC.
Dont worry about HV it will bleed off fast. Cant get you anyways unless you
stick your hand under the anode connector !

Good luck
Zeno 8)
LFOD !


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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Thu 26, 2017 2:48 pm 
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Hey Zeno,

zeno wrote:
I second Findm's opinion !
JVC was almost always always a cold joint under vert IC. Same with
Panasanic, Sony & Zenith. Its the first thing to check on ANY set with a vert IC.


Good to know. I'll give the chip a good look over with a magnifying glass, for sure.

Quote:
In fact we always checked it even if something else was done.
Look for apx 1" long IC on a heat sink with about 7 pins. Dont confuse with
the audio out IC.


I'll make sure that I look up all the chips and know what they do beforehand.

Quote:
Dont worry about HV it will bleed off fast. Cant get you anyways unless you
stick your hand under the anode connector !


True, but I've been "bitten" by the HV on a TV set before, and I have absolutely no inclination to revisit that situation again :D.

73, Randy AB5NI

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Fri 27, 2017 7:36 am 
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Hey Guys,

Well, the damn kid didn't show up until it was late in the day, so I just said to hell with it and setup to fix the Sanyo after I eat breakfast later on in the day. Can I use a small brush and vacuum out all the dust and stuff, and do I have to worry about jumpers being pulled off the PCB?

73, Randy AB5NI

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 Post subject: Re: HELP! TV Repair Noob :D
PostPosted: Oct Fri 27, 2017 10:49 am 
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Sure. Just be careful around the the neck of the CRT and the small circuit board with the CRT socket.

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