Hoffman TV - Improper Picture Height

There is a terminal lug strip labeled for testing voltages "A", "B", and "C". Are there any standard voltages these shouldbe or does it depend on the manufacturer?

Originally Posted by yagosaga

This is not really a good recommendation. It s better to check the circuits and to find the failure. So you have the opportunity to learn something.

I agree! I want to learn as much as I can about this. I feel I'm pretty good with radios. I remember buying a big lot of transistor radios on eBay. I fixed most of them from being dead and resold them. The electrolytic condensers all had to be replaced and many transistors did, also (generic replacements often work). But ah,. I'm getting off-topic.

I did make a list of all the condensers I need. I figure I'll buy 10 of each from Mouser so that way I'll have some extras. I only need 1-3 of each.

(MFD @ WVDC)
0.001 @ 400
0.0022 @ 400
0.0047 @ 200
0.01 @ 600, 1600
0.039 @ 400
0.047 @ 200, 600
0.068 @ 400
0.1 @ 200, 400, 600
0.22 @ 200
0.47 @ 200
4 @ 600 (four 1's in parallel)
10 @ 350
40 @ 350 (four 10's in parallel)
100 @ 350

I am thinking of getting axial aluminum electrolytic for the ones to replace the large filter condensers. Are there any recommendations for what to replace the smaller ones with? I was thinking of going with polyester film because they have high voltages for relativeloy low cost (under a dollar each from Cornell Dubilier).

None of the resistors look suspect. But I was thinking of replacing the small carbon comp ones anyway. What's anyones' takes on this idea?

[Adam]

What I usually do with the resistors, is not to replace them all, (while they do burn out from time to time, not nearly as much as the capacitors) but if you get the schematic it will tell you what the resistance from all the pins on the tubes should be usually to ground. While, this won't always allow you to check specific resistors, it will tell you if there might be a bad one in any particular area. I usually don't go pulling any resistors in any particular area unless this is off my more than 10% or so, and I am already sure it isn't off because of a shorted capacitor or something.

But then I don't always know what I'm doing, I'm not really a TV repair man, I just like to fix TVs in my spare time. I usually try to avoid giving technical advice unless I'm absolutely sure what I'm saying, but it has been really slow here this week and I want to write something just to give people something new to look at.

[yagosaga]

Originally Posted by wa2ise

I don't know about that. The paper may have acid in it, and may have reacted with the moisture to degrade the foil and the paper. MY father had mentioned this cooking method, but that was 35 years ago. Might have worked back then, but I wouldn't trust it today.

Several people here have tested this method with success. Even the cooking of bad flyback transformers (those with open coils) brings new live to them. A friend of mine has done this with a flyback for the RCA ctc5. If you try it, you should test the capacitors with a high voltage capacitor tester at 500 volts.

[bgadow]

I never bother with resistors unless there is a problem. The most suspect would be those with higher resistance ratings, especially stuff like 1 meg or more. Even if a resistor has drifted a little in value, it won't drift so far out like a capacitor would.

I still say condenser, because that's what it is. It condenses, it doesn't capacit. I also say cycles-per-second, not Hertz. But that's just me. (-:

Well I ordered the condensers from Mouser over teh weekend. Hopefully they'll be coming any day this week and I can start fixing the set! I ordered Cornell Dublier Polyester Film ones to replace the paper and plastic ones, and radial and axial electrolytics for the large filter condensers.

Received the condensers today! I will start replacing the old ones. SInce the chassis is for the most part solid, I won't worry about underside looks. For the paper condenser on the top-mounted lug strip, I will hollow out the old cardboard tube and install the modern one, and seal it with wax and hot glue. I'll post some pics when I do that. As for the large input condensers, I'll leave those mounted on the chassis but I will disconnect them and mount the modern ones underneath. I have read of cutting them open and potting new ones inside, but I don't want to ruin them. It'll be fine to hide modern ones underneath... there's enough room.

Here is some progress on the rework in the input section. Note that I don't have 40 uFd condensers, so I needed to make an array of four 10's... in two places.

This is becoming messier than it was to start with! Of course, replacing single paper condensers with ceramic ones reduces clutter dramatically. I find myself double-checking my double-checking to make sure I am using the right components.

It's just so hard to beleive that the new components of the same rating and value are about 1/20th of the size of the original. I can't help but worry if I am installing a wrong part! :-)

[bgadow]

I usually use a 47mfd to replace a 40, but what you are doing will work fine, too. I know that I have double checked myself sometimes when those new parts just looked too small! Especially with lower value paper caps. A .001 in paper isn't much smaller than a .01 but some of those new ones are tiny.

Looking forward to the finished product!

I cleaned the tubes... this 6DT5 (vert opt) looks burnt even after cleaning... I wonder if it could be the culprit after all? Not that replacing the condensers was a bad idea. I don't have a tube tester so I need someone's expert advice. Is it me, or does the tube on the left look like it's on its way out?

Ok I put the set back together with most of the condensers replaced (couldn't get some values but only about three).

I GOT FULL VERTICAL SIZE! WOOT!

But now there is another problem. Set is only snowy with a thin brighter line down the center, top to bottom. I'm thinking it could have something to do witht he yoke, which spins freely on the neck.

I also might not have reinserted the yoke plug right in the socket. I speculate this because although I am getting full vertical, perhaps it's not being directed where it should. Let's see what the Sylvania book says.

Even though this is a Hoffman TV, my Sylvania book, which I got for only $0.99 on eBay, is very useful in troubleshooting. "Servicing TV receivers" by Sylvania Electric Products Inc. First Edition 1950. It feaures test patterns and schematics of what to look for, and troubleshooting tips. I highly recommend a book like this.