Zenith 19EB12 B/W TV (Quadrapong)

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Hey all,

This may be semi-OT, but has anyone messed with the black and white TV sets used in early Atari cabs? More specifically, my Quadrapong has a Zenith 19EB12 that has issues with vertical hold, horizontal hold, and vertical linearity. The horizontal hold seems to settle down after the thing is on for a minute, so immediately I'm thinking bad caps, but there's only 1 electrolytic on this thing that's already been replaced. I've never worked on a monitor/TV of this vintage and I'm open to any suggestions, including possible replacement ideas. I would think I could find another TV with VHF and UHF inputs as a replacement. I did pick up a 13" B/W with those inputs at a thrift store, but I can't get any picture out of it that's even close. Any advice or input would be appreciated. Thanks!
 
The TV in the Quadrapong has been modified to accept composite video over the antenna inputs. An ordinary TV will not work.

Is this a solid state television, or is it a tube set?

Post some pictures of the chassis.

-Ian
 
The TV in the Quadrapong has been modified to accept composite video over the antenna inputs. An ordinary TV will not work.

Is this a solid state television, or is it a tube set?

Post some pictures of the chassis.

-Ian
Thanks very much for the reply. I was looking back at a webpage I found that has samples from a book called "Consumer Electronics For Engineers." They used the 19eb12 as an example as they break down how it works. Being for engineers, the math quickly went over my head. :eek: It does say in there that it's discrete logic based so I'm guessing would mean a tube set? Here's a quick pic of the tube/chassis. I plan to pull the thing tomorrow so I can get better pics, but maybe this helps somewhat.

DSCN0717.jpg
 
OK, that's a solid state set. No tubes, unless you see some hiding in there :D

Have you replaced the main filter electrolytic? That's the big metal can in the upper left. It's probably a multi-section electrolytic.

-Ian
 
OK, that's a solid state set. No tubes, unless you see some hiding in there :D

Have you replaced the main filter electrolytic? That's the big metal can in the upper left. It's probably a multi-section electrolytic.

-Ian
Duh I guess I wasn't thinking straight when I thought it might be tube based. No I haven't replaced that large filter cap yet. In fact I will admit I didn't even notice it until you mentioned it. :eek: I'l take a look at its value so I can replace it. I've never deal with a multi-selection cap. Are they possibly hard to find? BTW, just for the sake of documentation if anyone runs across problems with this same monitor, here's a link to a page that talks about it. The math the use to explain how things operate goes over my head, but there are some schematics.

http://books.google.com/books?id=_s...0CB4Q6AEwAg#v=onepage&q=zenith 19eb12&f=false
 
I'l take a look at its value so I can replace it. I've never deal with a multi-selection cap. Are they possibly hard to find?

Yes. You'll probably never find another one with the same values. But it doesn't matter - a multisection cap is simply multiple normal electolytics in one can, with all the negative terminals tied together. You can replace it with suitable individual electrolytics wired appropriately.

-Ian
 
Yes. You'll probably never find another one with the same values. But it doesn't matter - a multisection cap is simply multiple normal electolytics in one can, with all the negative terminals tied together. You can replace it with suitable individual electrolytics wired appropriately.

-Ian
Thanks again for the reply. Even if I found a replacement I would question if it was too old to be reliable. On another note, I found a website that will sell a copy of the manual for $22.
 
For television sets, I've found that the best reference you can get is the Sam's Photofacts. That's probably what you've found - especially since Sam's sells them for $22 each :D

That set is in folder 1385-3.

My local library actually has a subscription to Sam's, and has all the folders in their reference section. When I need a PhotoFact, I just look up the chassis number on the Sam's site, then go down to the library and look it up. Your mileage may vary as to wether your library has them or not.

-Ian
 
For television sets, I've found that the best reference you can get is the Sam's Photofacts. That's probably what you've found - especially since Sam's sells them for $22 each :D

That set is in folder 1385-3.

My local library actually has a subscription to Sam's, and has all the folders in their reference section. When I need a PhotoFact, I just look up the chassis number on the Sam's site, then go down to the library and look it up. Your mileage may vary as to wether your library has them or not.

-Ian
Thanks again for your reply. Haha yes it was Sam's Photofacts website. I'll have to look into my local libraries and see if any of them have a subscription. Thanks for that tip. :)
 
Tore into this tv/monitor a little bit tonight. It wasn't too hard to take apart other than having to unsolder one wire from a pot to allow the chassis to separate from the rest of the frame. I determined all the values on the multi-selection cap and noticed a number of axial lead caps on the bottom side. I figure I might as well replace those while I'm in there. One thing that seemed odd is how those caps are installed. The leads go up into those posts that you see on the top side of the chassis and usually another component lead or two are in there with them. I can only assume those posts are filled with solder and so i need to heat them up from that top side to pull them out from the bottom. Still hoping to find Sam's Photofacts available at a local library. That would really help in identifying any cap values I'll need. The flower pattern paper on the frame leaves little doubt this thing is from the 70's. :D
 
Those solder-filled posts are classic Zenith constuction - they stuck to using a hand wired chassis while a lot of other manufacturers went to all circuit board based construction. That's part of the reason why Zenith sets were so reliable. You can either heat up the post to pull out the component lead, or you can clip off the old component, crimp the leads of the new one onto the old one's legs and solder it together. You might have to do that in some places since you'll probably be replacing the old radial caps with modern axials, and won't have long enough legs on the new parts.

-Ian
 
Those solder-filled posts are classic Zenith constuction - they stuck to using a hand wired chassis while a lot of other manufacturers went to all circuit board based construction. That's part of the reason why Zenith sets were so reliable. You can either heat up the post to pull out the component lead, or you can clip off the old component, crimp the leads of the new one onto the old one's legs and solder it together. You might have to do that in some places since you'll probably be replacing the old radial caps with modern axials, and won't have long enough legs on the new parts.

-Ian
Yeah I had thought about just clipping the old caps and soldering to the legs. It might make it a lot easier in the long run, plus what you mentioned about axial legs not being long enough.
 
Didn't have any luck finding a local library that has access to the Sam's Database, but I did find a place online that sells original copies for 1/3 of what the Sam's website is asking. I suppose I could have just taken time to look at the cap values when I had the thing apart, but I'll admit I'm lazy. ;) It never hurts to have a copy of the service manual though.
 
Okay so my copy of the manual arrived today and I now have a list of caps I can track down. I started looking at the multi-can cap replacements and the first one is a 200uf 175 volt. Mouser has a 200uf 200v at 36 buck a pop. :( Before I get too far along in hunting down caps, is there any chance I could go at all higher in the microfarad rating? I know the general rule is you can go up in voltage, but never down and I've always thought the capacitance has to be exact. I have seen other mentions of people using different capacitance so is there a general rule for doing that? Thanks!
 
In general, you don't want to mess with the microfarad rating.......but, it can be fudged a little. In your case, I'd go with a more common size (like 220µf). Most can caps in monitors are used for filtering. Filtering caps have way more leadway when fudging with the value.

Edward
 
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