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  #1  
Old 09-23-2012, 09:01 PM
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New Project - 1980 Zenith Corner TV (with Shorted HOT)

Model #SL2541X. I've had this TV for about 6 years now. I'm only now tearing into it. It was DOA when I rescued it. Putting a new fuse in it just to test blows the B+ fuse. This is a System 3 TV. And I did just buy the Sams for it.

So last night I finally started going through it. I removed the HV/power module with the HOT on it. Turns out that may be the culprit as I have a short in both directions between Base and Collector on it.

I'm going to be ordering the new HOT for it, but my question is are there any other known issues with this particular module to cause HOTs to blow? Physical inspection everything looks fine. I haven't done any further testing. The flyback does have 2 stickers that say Re-Built on it. I am hoping I don't have a shorted flyback.


Everything else looks good in it.
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  #2  
Old 09-23-2012, 09:29 PM
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Ah, the good old 9-160 board. Wish I had a buck for every one of those I worked on back in the day. You might be able to find an entire replacement module on eBay if you look.

The HOT will occasionally fail all by itself, but check for bad soldering on flyback pins and all the rest of the parts in the horizontal sweep circuitry. I seem to remember a diode and cap near the HOT that often went south, as well.
Check the 4-legged safety cap, too.
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Old 09-23-2012, 10:10 PM
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they were good money makers. i would try to find a nos module if it were mine.
steve
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  #4  
Old 09-23-2012, 10:11 PM
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I agree about the bad solder connections.

I had one of these with a shorted HOT, a shorted diode, and some other parts that I don't recall at the moment. After I replaced those parts, the flyback arced violently. I killed the power before the arcing flyback took out the other parts, found a flyback from a junk board, installed it; and, the TV worked fine.

I seem to remember a small electrolytic cap in the HOT emitter circuit that would fail, just like in the older CCII sets.
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Old 09-24-2012, 09:13 PM
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I remember replacing the transistor and 2-3 capacitors as standard practice on these sets.
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  #6  
Old 09-24-2012, 09:19 PM
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A shorted horiz out transistor could take out the flyback, making it bad enought to blow up a replacement transistor. Not sure how you test a flyback...
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Old 09-24-2012, 09:57 PM
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Thanks for all the replies so far

For starters, right off Ebay someone was selling 3 NOS HOTs for this TV with free shipping which I snagged this afternoon.

I'll start testing all the caps and nearby components when I get a chance. Just to be sure I will also resolder all connections on the flyback as well.

N2IXK - the board in mine is a 9-160-04. Nothing on Ebay right now, but what other boards, if any, will sub in there? I keep seeing 9-160-06 stuff from other places or old auctions.
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Old 09-25-2012, 11:07 PM
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I am almost positive that you can go with the higher suffix, just don't go lower. They were usually backwards-compatible.
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  #9  
Old 10-06-2012, 03:23 AM
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Well here is my status update on this set:

New HOT installed. Resoldered all flyback connections just to be safe. All other components check out on that board.

New 4A line fuse installed. Put the TV back together. Pressed power, and nothing.

Turns out the B+ fuse on the board (turns out I actually have a 9-160-06 board), the 125mA fuse, is not completely blown, but it reads a consistent 28 ohms of resistance. So I shall be ordering a new fuse for that before I can continue testing.
(btw, I messed up in my earlier post, it was the 4A line fuse that was blown when I got the TV, not the 125mA B+ fuse)

Now last time I tried this set about 4 years ago (because I didn't know what was wrong), I installed a new 4A fuse, and it powered on for a fraction of a second: Degauss coil and channel number lit before it blew again.


And my final question for the night: This is due to my failure to have taken pictures or notes on this while taking apart, but on the 9-159-01 Zoom module, does the yoke connect directly to 9C? I ask because the connector coming from the yoke says 3D, but 3D is actually connected from the 9-160 board to 9B on the Zoom module.
I just want to make sure I plugged it back into the appropriate slot (the way the wires are routed, dressed, and length, there is no other slot it could plug into. All other slots are filled.)



And side note, I did test the CRT with a Sencore CR7000: It has very good emissions on all 3 guns, but I cannot get the blue to even go into cutoff (doesn't even move), and red just barely makes it. Green is fine. So we'll see how well greyscale tracking is once I get this set operational.
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Old 10-06-2012, 10:34 PM
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And side note, I did test the CRT with a Sencore CR7000: It has very good emissions on all 3 guns, but I cannot get the blue to even go into cutoff (doesn't even move), and red just barely makes it. Green is fine. So we'll see how well greyscale tracking is once I get this set operational.

your tube is weak seen many of them i mean lots ans lots of them sorry. steve
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Old 10-06-2012, 10:51 PM
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Those early 23V/25V inline tri-focus CRT's didn't hold up nearly as well as the older delta gun CRT's. I agree that your tube is weak; but, you should be able to get a somewhat acceptable picture on it. Of course, it will only get worse over time. I've seen these that were so weak that no gun would reach cutoff and they'd all 3 read in the very low end of the "BAD" scale. As you can imagine, the picture wasn't too good on those really weak ones.

And, I think the reading on that B+ fuse is normal. I think those are of the slo-blo type and they will show some resistance.
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  #12  
Old 10-07-2012, 01:52 AM
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Quote:
Originally Posted by radiotvnut View Post
Those early 23V/25V inline tri-focus CRT's didn't hold up nearly as well as the older delta gun CRT's. I agree that your tube is weak; but, you should be able to get a somewhat acceptable picture on it. Of course, it will only get worse over time. I've seen these that were so weak that no gun would reach cutoff and they'd all 3 read in the very low end of the "BAD" scale. As you can imagine, the picture wasn't too good on those really weak ones.

And, I think the reading on that B+ fuse is normal. I think those are of the slo-blo type and they will show some resistance.
And worst case, I'll try the restore functions on my tester if it gets bad. I don't even know how well this set will perform now.

Completely slipped my mind about that being a slo-blo fuse. I guess I just didn't think it would have been that much resistance. Well, looks like I may have another problem then. I'll look at it more tomorrow. Good news is it didn't blow my 4A line fuse.
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  #13  
Old 10-07-2012, 02:45 AM
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Ok, put that slo-blo fuse back in (that was just a brain-fart there, ignore my statements about it, I was tired that night heh), and tried it again.

That Space Command switch must be dirty or something, because I know I put it in the Manual mode to, what I assume, allow the local keypad to work. Last night it did not do anything.

Anyhow, it turned it on, and it is not blowing a fuse anymore. In fact, HV is coming on, and deflection is happening (although the set was not on long enough to warm up.)

It is squealing quite loudly. I tried to leave it on and my cats went running from the squealing. It started changing pitch after about 5 seconds and I hurried up and shut it back off again. Normal static discharge when shut off.

I went to check something, and tried it again, powered on, but now it squealing even louder.

It is not blowing any fuses now. It is staying on, and I heard audio. I never had the set on long enough to see if it produced any picture yet.

So is there anything I need to be concerned with here? I resoldered all the flyback connections. All the surrounding components on that board do check out OK when I had it out. Could it be the flyback core singing or other component? It was quite loud and kept changing loudness/pitch. Definitely does not sound good.

Last edited by tv beta guy; 10-07-2012 at 02:18 PM.
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  #14  
Old 10-07-2012, 12:27 PM
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If the horizontal osc. is far enough off it's proper frequency that could cause squealing.
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  #15  
Old 10-07-2012, 03:32 PM
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I had a squealer Zenith once. We were able to snug up the pole pieces by gently tightening the nuts on the the FBT. Watch out, as you can crack the pole and ruin it.
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