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

These are bulging from the middle of the cap down towards the board. Hard to tell in the photos, but if you look at them from the top down, they are definitely bulging. If that is glue, sure did not adhere very well. I can wiggle the caps in place and it sure seems like the only thing holding them in place is the solder connections. I will report back when I remove them from the board if that was a horrible glue job or if they were leaking. I just ordered the replacements from Mouser, along with some resistors for my Telebar.

I just popped mine open and it's a little different than yours. It has some surface mount electrolytics and I see date codes from 2001.

I see a little white crust around the negative lead of C10, but the others look OK. I'll pop out the board and check with an ESR meter later. I also plan on making a dipole antenna using 75 ohm coax.
https://farm8.staticflickr.com/7148/...5becb04d_z.jpg

You probably know this, but just for the record -- an electrolytic may look perfect but still be total junk inside. If you see one that's bulging or exploded, of course that's a bad sign. But the innards may have gone bad even if the outside doesn't shown signs of catastrophic failure. The bad electrolytics in my modulator looked fine on the outside. Only an ESR meter can tell you what's really going on in there.

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

I've used multiple agile modulators to create my own cable headend, so I can change channels on a vintage TV and find signals, just like in the olden days. Use a multiport cable splitter backwards as a combiner to merge all the outputs together.

Some of the 1970's era stereos I've recapped have had glue like stuff under the bigger caps. I assume that it was to hold them in place while they were soldered by the automated machines. Some of them had corrosion under them, some not.

I'm wondering if there's a common source of interference like lights, computers, etc. causing this. Does going to a half wave antenna change it? I'm curious as I just ordered a Standard agile modulator, so I'll see what it does. I was looking for a fixed channel 6 one thinking that I could also use it for FM radio since we don't have a station at 87.7 around here. But, they were too expensive or were mini rack ones that need a power supply.

It seems the Drake ones have gone up in price too since Bob did his first video. I guess that's the power of his videos! Please just don't do any on Pico, or Scientific Atlanta, or Holland, etc.!:D

All my caps tested good with an ESR meter. Here's what's inside for the curious. Seems to me they could have made these a lot smaller :scratch2:

IF modulator in the lower left.
Programmable RF modulator is the three shielded boxes.
Power supply along the right edge.
RF amp is the small green module at the rear.

https://farm8.staticflickr.com/7196/...967e1edd_c.jpg

I guess if they are intended to fit in a rack with other components, you make 'em this size regardless of how little is inside.

Phil Nelson

We're all in modulator land!! :D

Sure, but I meant depth. They make many other models that are less deep so I was expecting there to be more inside.

Indeed! Here are the insides of the BAVM-z model.
https://farm4.staticflickr.com/3769/...24dbc48c_c.jpg

Could it be that some of the extra space is for optional modules? I have the AM60-550A and I recall the manual mentioning several options.

I got mine at a hamfest last month for $5 and the seller seemed to be glad to get rid of it. I don't think it had ever been used. I haven't used it much yet, but I have not noticed any hum bars.

The "goo" that is in the picture above is most likely glue placed to keep the electrolytic capacitor from moving during shipping. Sansui did the same thing in its receivers.

But this thread has moved in the right direction. I have personally experienced the same problem and it was electrolytic capacitors that were going south in Blonder Tongue Agile Modulators. They are easy enough to replace and you can get some 105°C capacitors that will likely outlive me. Easy fix and permanent fix for sure.

I still have not removed the caps yet to see if it is indeed glue, but even if it is - still replacing them. I do not yet have an ESR meter, but this is such an easy service at a low cost, makes sense to do it while the unit is open. If it fixes the sound bars - great!!! If not, will try the next "solution." I like to start with the easy, obvious stuff and move forward. Especially since I am learning and only been doing this stuff for a year. I am one of those folks that learn best by DOING. This forum has turned into a valuable tool in that learning process for me and I want to thank everyone here for their willingness to walk a newbie through question after question. Really appreciate it.

Thanks.

That glue can be a real problem. It was also used in a heap of 80s TVs, and had the bad habit of going conductive after a while. It caused a lot of easy to fix faults. It may be a reason why you get the bars even when the caps test ok.

If it is glue, going to try and remove it as carefully as I can. It seems to flake off with not too much effort - so should be fairly easy. It is VERY dried out.

Here is an interesting design for a folded dipole that has the matching stub for 75 ohms, which cannot be omitted.

http://www.electroschematics.com/26/...ipole-antenna/

I've seen this "hum bar" when there is an impedance mismatch in the modulator-tv coax.

...

That's an interesting theory, but not sure it applies to my situation. My modulator has been working fine for a year. Just within the past three weeks has the scrolling bar symptom started - so I don't think it is a grounding issue.

I will see if replacing the 'lytics fixes it, and if not go from there. Waiting on the caps from Mouser along with a bunch of other parts.

Thanks for all these theories, as it gives me a good road map to follow if the first "fix" accomplishes nothing. :D

Recapped agile modulator tonight and scrolling bars GONE!! :banana:

Two of the 4 caps had nasty corroded leads when I unsoldered them from the board. But none had actively leaked. That was indeed glue on the board from the last install of these caps. I was able to clean the glue off the board easily as well.

Thx to those who chimed in on this issue. Video here:

http://youtu.be/wgrp8HOewxs

Yay! I love simple solutions.

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

Me too!!!! Thanks for the info on your site too. Was very helpful!!!! :D

Fortunately, the symptom is very similar to the same problem with a B/W television. Scrolling black bars up the screen were usually failed electrolytic capacitors in the power supply. Of course, our modulators are not exempt!

Glad you got the problem solved quickly and easily.

What type of solvent did you use to remove the glue?

Turns out the glue was SO dried out, it flaked off with my finger nail completely. Did not need to use any solvents. :thmbsp:

I've got a strange issue with my Blonder Tongue CAMS-60. It's probably been like this for a while, but it bugs me. It's not "terrible", but if there's something I can do to fix it, all the better :)

Is there a place on the board to align the audio signal? It's not the audio adjustments on the front. I get slight whistling "S"s from everyone on TV that sounds out a "sss".