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 Post subject: Tip for grounding problems on the Motorola VT-71
PostPosted: Apr Fri 21, 2017 1:58 am 
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I finally solved the grounding problems on my VT-71 by cleaning and coating all the component rivets on the chassis with "wire-glue". This was the advice of my repairman who could not figure-out the problem when he had it on the bench. It takes some time and patience, but I was so pleased with the results. No more intermittent buzz in the audio and flicker in the video. I got the product on Amazon and would highly recommend it!
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 Post subject: Re: Tip for grounding problems on the Motorola VT-71
PostPosted: Apr Fri 21, 2017 2:36 pm 
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By "component rivets" do you mean terminal strips, the rivets that secure the tube sockets as well as some other major parts to the chassis, or something else (I've never heard that turn of phrase before)? In the two cases I can think of what you really have is cold solder joints, and or bad grounding to chassis of the tube socket mount flanges...The 'proper' way to deal with those issues is to get an old school 75-150W soldering IRON (not a gun) and re-flow those solder connections adding some fresh solder and to add solder joints on riveted metal part to chassis joints. I have 2 such irons and use them to make new chassis ground solder connections and to add and remove direct chassis mount can lytics regularly. Those irons could solder the bumpers of two 70's Buicks together...If I ever found 2 parked that close. :mrgreen:

I can see one good use for that glue though...If a non-heater lead breaks off flush with the glass on a CRT with a bakelite base that glue would be a better way to attach a new lead to the glass than solder (change temp of glass too quick and it cracks).


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 Post subject: Re: Tip for grounding problems on the Motorola VT-71
PostPosted: Apr Fri 21, 2017 5:12 pm 
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Corrosion at riveted chassis connections is, by far, an unrecognized problem. In '85 I restored a Raytheon Belmont, even after careful replacement of defective components video/audio was poor. Continuity measurements said nothing was wrong. Poking components that were connected to tube socket ground ring in the video cased a momentary flash of improved signal. Since the chassis was plated steel soldering all the rivets that were associated with ground connections proved to be a solution. I a post some six months ago another ARF user had encountered this same phenomena. His measurements could not prove the chassis bond was defective but soldered the connections regardless...

This compound is useful when the location cannot be soldered.

IMHO, this problem is not just associated to TV's, radios can experience this. I often wonder if some of the "mystery" defects reported to ARF are no more than poor chassis connections. Especially when the second or third post in the topic includes chassis cleaning, often to remove rust. So, clearly chassis connections could be faulty...

Chas

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 Post subject: Re: Tip for grounding problems on the Motorola VT-71
PostPosted: Apr Fri 21, 2017 6:08 pm 
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Chas wrote:
This compound is useful when the location cannot be soldered.
Yeah, I can see uses for this product, which appears to be graphite-filled glue.

Silver-filled epoxy is a similar product, presumably with more sticking power than everyday glue. I used it to repair a lead on a CRT base that had broken off nearly flush with the glass (see http://antiqueradio.org/CapehartFarnswo ... vision.htm ).

Image

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The silver-filled epoxy worked well in that case, but it's quite expensive. And epoxy might be overkill in some situations, anyway, where the wire glue mentioned by the OP would work fine.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html


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 Post subject: Re: Tip for grounding problems on the Motorola VT-71
PostPosted: Apr Sat 22, 2017 7:21 am 
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Interesting info guys. Excuse my terminology as I am a total novice with electronics even though I've been in the hobby for 35+ years! :oops:
Yes, the rivets in the chassis for tube sockets and various mounts. Like they say "the proof is in the pudding" and scouring, cleaning, and using the wire glue immensely improved the performance of my set.


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 Post subject: Re: Tip for grounding problems on the Motorola VT-71
PostPosted: Apr Sat 22, 2017 12:45 pm 
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The problems that I have had with rivets were when the chassis was aluminum. The terminal strips are often tin-plated brass. So, you can see that there is a situation of dissimilar metals causing electrolysis. The inexpensive fast and permanent solution that I always use is to drill out the rivet and replace it with a screw, star washer and nut. Of course, if you are drilling out a rivet, there is always the possibility of the drill bit (especially a sharp one!) can grab the terminal strip and spin it around causing much collateral damage.

Just a thought...

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 Post subject: Re: Tip for grounding problems on the Motorola VT-71
PostPosted: Apr Sat 22, 2017 1:11 pm 
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Fun and informative article:

http://www.petervijn.org/2013/01/electr ... e.html?m=1


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 Post subject: Re: Tip for grounding problems on the Motorola VT-71
PostPosted: Apr Sat 22, 2017 1:15 pm 
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Don Cavey wrote:
The problems that I have had with rivets were when the chassis was aluminum. The terminal strips are often tin-plated brass. So, you can see that there is a situation of dissimilar metals causing electrolysis. The inexpensive fast and permanent solution that I always use is to drill out the rivet and replace it with a screw, star washer and nut. Of course, if you are drilling out a rivet, there is always the possibility of the drill bit (especially a sharp one!) can grab the terminal strip and spin it around causing much collateral damage.

Just a thought...

I spoke to my repairman about more drastic solutions to chassis rivets and he's against it. Hammering, soldering, drilling is risky and may cause further problems. The wire glue is simple, easy, and just a logical solution. It sure is worth a try if you have a Motorola VT-71 with noticeable grounding problems.
Thanks for the link WeekendHacker!


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 Post subject: Re: Tip for grounding problems on the Motorola VT-71
PostPosted: Apr Sat 22, 2017 1:29 pm 
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Another very creative use for glue:

https://youtu.be/_gyvipBs6Vs


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 Post subject: Re: Tip for grounding problems on the Motorola VT-71
PostPosted: Apr Sat 22, 2017 6:14 pm 
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decojoe67 wrote:
I spoke to my repairman about more drastic solutions to chassis rivets and he's against it. Hammering, soldering, drilling is risky and may cause further problems. The wire glue is simple, easy, and just a logical solution. It sure is worth a try if you have a Motorola VT-71 with noticeable grounding problems.
Thanks for the link WeekendHacker!


I can see how hammering and drilling would be risky. But I don't see soldering as risky or difficult. Of course you would have to have a big enough soldering iron. But with the right iron, soldering should go as quickly as applying glue. But then I use one of the temperature controlled irons with a high wattage element in a reasonably small form factor.

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 Post subject: Re: Tip for grounding problems on the Motorola VT-71
PostPosted: Apr Sun 23, 2017 4:03 am 
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I don't see careful drilling as being extreme. I would be inclined to do that before using any kind of glue or paste. But again, it isn't my set.

Hammering is another thing and I never advocated doing that.

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 Post subject: Re: Tip for grounding problems on the Motorola VT-71
PostPosted: Apr Sun 23, 2017 4:18 am 
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Don Cavey wrote:
I don't see careful drilling as being extreme. I would be inclined to do that before using any kind of glue or paste. But again, it isn't my set.

Hammering is another thing and I never advocated doing that.

I must say that I'm not qualified to mention which is the better way to do the job, but it seems the wire glue is the least obtrusive approach to creating a bond with the rivets and the chassis. I can't see why such a simple and effective solution should be questioned.


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 Post subject: Re: Tip for grounding problems on the Motorola VT-71
PostPosted: Apr Sun 23, 2017 8:19 am 
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decojoe67 wrote:
Don Cavey wrote:
I don't see careful drilling as being extreme. I would be inclined to do that before using any kind of glue or paste. But again, it isn't my set.

Hammering is another thing and I never advocated doing that.

I must say that I'm not qualified to mention which is the better way to do the job, but it seems the wire glue is the least obtrusive approach to creating a bond with the rivets and the chassis. I can't see why such a simple and effective solution should be questioned.


Because most of us have TVs or radios with many, many solder joints that are approaching 100 years old that still function as designed. Because there's no track record of how stable the glue is over time. No data points. Does it disintegrate in 5 years? Does it eventually lose conductivity? Does the resistance of it matter (vs solder)? Does it retain humidity and eventually rot out the very joint it was intended to repair?

Does it make the TV smell funny?

Questioning isn't condemning. It's just healthy skepticism. The basis of reason and science.

The value of using it (over careful soldering or careful drilling) appears to be convenience. It's easier. We've been around the block enough times to know the easy solution is rarely the best one.

Rarely but not never. Your idea is noted and will likely be tried and evaluated by many. It may end up being mainstreamed. Or not. Depending on how it survives healthy (and appropriate) skepticism.


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 Post subject: Re: Tip for grounding problems on the Motorola VT-71
PostPosted: Apr Sun 23, 2017 5:24 pm 
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In my case I have done a lot of soldering. So to me soldering seems to be the easy and simple thing to do.

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 Post subject: Re: Tip for grounding problems on the Motorola VT-71
PostPosted: Apr Sun 23, 2017 5:46 pm 
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I didn't get any noticeable smell with the glue. It dried like a blob of epoxy was painted over the rivets. I can't imagine how long it would take to break down. The cabinet will likely cave in on itself from age before then! :D
By the way, I understand the healthy skepticism and find all the comments interesting ones.


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