Scrolling bars using agile modulator
 

I have noticed that recently both my working vintage sets, when using my Blonder Tongue agile modulator, have scrolling bars moving up the screen. This morning I was watching Bob's latest YouTube video and whatta ya know . . . he mentions this is sometimes an issue when using these units or it could be a video source issue as well. Has anyone identified what these bars are caused by? Can see them in Bob's below video.

https://www.youtube.com/watch?v=_oNk...em-subs_digest

He mentions it at the 22:20 mark for a few minutes.

I have been using this unit for the last year and it has only started within the past few weeks. Has anyone identified the issue and figured out how to fix it? If anyone has diagnosed and fixed this I would love to hear about it or be directed to any old forum posts that talk about these bars and what causes it.

Thanks!!!

Earlier thread here: http://www.videokarma.org/showthread.php?t=260707

Lots of ideas, but it appears that the "root cause" has yet to be determined.

jr

I used three different modulators - two BT and a Drake. All had the bars to varying degrees.

I received some comments that it's caused by the 60 Hz house wiring somehow ?

Interesting that mine has not done it until about 2 weeks ago. Been fine for almost a year. I built a dipole antenna for mine. My modulator is fixed on channel 7.

Seems to be worse when the unit is first turned on, and gets better as it is on longer. At first I thought this was one of my sets. Tested all the tubes, etc. Then I realized that both sets show the scrolling identically and it improves on both sets as the unit is left on. Never goes away 100%, but better on my Admiral console than on the 7 inch set.

I could see leaky lytics in the BT causing this. I think I saw Phil posted something about that. Maybe worth popping mine open and testing those. Especially since my symptoms just started and have been fine for a year.

Yes, my Blonder-Tongue agile modulator developed moving horizontal bars after a couple of years, which condition was cured after I replaced the four power-supply electrolytics. This article has some details:

http://antiqueradio.org/HomeTVTransmitter.htm

Other causes may be at work, but I always like to eliminate the obvious before chasing after the exotic.

Regards,

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

Thanks Phil! I will check mine out. Hopefully it is something simple like this in my case instead of some unknown interference. I see here some other guys have gone crazy chasing this issue with no luck.

The "scrolling bar" problem is most definetly caused by failing electrolytic caps in the power supplies of those modulators. this was a common problem with them as those agile modulators were powered on 24/7 while they were in service. this problem was also present in cable boxes as well. i used to sevice these kind of things.

try connecting it directly to the set with a cable (will need to turn power down to min).

Thanks. I'll crack mine open and replace. Looks fairly easy and straightforward.

Well after opening up my Blonder Tongue agile modulator, what do I find?? Bulging, gooey, leaky lytics!!!! Thanks to Phil and Bob for pointing out this possible issue.

Now to order four 1000 uf @ 35 v caps and replace.

Thanks gents!!! :D

I replaced all of the electrolytics on my BT modulator and it had zero effect on the scrolling bars. I highly suggest you follow Dave's advice and wire the unit directly to the TV and see if this solves your problem. I went through two modulators as well as power supply electrolytics all with no difference. Hard wiring the modulators to my sets cured the symptom entirely and gave me a much cleaner signal in the end.

Yikes! I'd better check mine too. Is that goo from really from the caps or just glue to hold them in place ? I've never seen caps leak that much. Usually the tops bulge and start to crack along the "X"

Sure, but why use a huge modulator with a RF amp for one set ? You could get a much small, less expensive modulator for direct drive.

You could...but why would you :scratch2:? I'm using two of them to drive two different channels to multiple sets. Cheaper modulators don't usually give you channel selection beyond 3 and 4, besides I didn't want to hook up plastic fantastic modulators to my sets, just didn't seem right.

There are plenty of quality options between crap and a full blown agile modulator. For example the BAVM-z series. Just select some in the frequency of your choice for 1/10 the price and 1/5 the space of an agile modulator.

https://farm8.staticflickr.com/7037/...fd3c59d7_z.jpg