OK, I've been trying to get this working correctly but I have a problem with bars or darker areas scrolling slowly upwards on the screen.

None of the adjustments on the Modulator affect the bars but they do seem to do their intended functions like increasing or reducing the levels.

I have two different BT Agile Modulators and they both do the same thing.
I've also tried two DVD players and different Discs, it's noticeable on different TV sets also, not just this little cheap one.

Any suggestions I can try?

Hi Eric,

Slowly scrolling bars are caused by 60 or 120 Hz modulation of something in the video. It's possible that your modulator needs one or more power supply filter capacitors replaced. Another possibility is a ground loop or open ground/shield on the video cable feeding the modulator. And I suppose another possibility is some AC hum in the video source itself.

That looks like video ground loop to me. This can occur when the transmitter and TV are on different legs of the 240 line. You can get a video ground loop isolator (pricey), or use an isolation transformer for the transmitter (if it uses a switch-mode power supply). You may have varying degrees of success with these methods.

I think I cleared it up mostly.

The first time I tried this I was using an old pair of rabbit ears for the transmitting antenna, I just stuck one leg of the flat lead in the F connector and it worked really well.

Between then and now I thought I'd improve it a little, I put together a short rod antenna with about 6 feet of Co-Ax cable and an F connector that would screw directly into the Modulator, it turns out the Rabbit ears make a much better picture.

The other antenna reduced the power so much the picture was snowy from 20 feet away.

OK, it has good sound and good picture but I do still have some wide bars rolling through the picture.

I posted a video if anyone would like to take a look and see what they think the problem might be.

It's most obvious around 26 seconds when the credits fade.

http://www.youtube.com/watch?v=hvsYV2kfjiE

I just received in the mail, a used BLONDER TONGUE AGILE MODULATOR AM60-450. It does the same thing. And I was thinking power supply capacitor as well. Since it is being sold as used, that could be the reason it was taken out of service.

I do have some B/T BAVMz modulators too. They are tiny in comparison. The only one that I have used so far is for Channel 7 and it works fine. I did however have to replace the voltage regulator IC.

I will be interested to see how this thread progresses...

try a direct cable connection, I get that when using like a transmitter (antenna connected rather than cable hookup).

Perhaps the direct connection resolves the ground loop

But that is what we want to use them for, a transmitter!

Yea I know, just a good check to see if it fixes the issue, then you can know its not a problem with the modulator per se

Ah, you are transmitting. When I first saw this I was thinking about a ground loop that was causing current to flow through the video cable between the player and the modulator. But that would produce one bar and it would be broader. So It can't be a ground loop.

When you transmit, you can pick up interference from any source. Given the two narrow bars, a likely suspect is a power supply using solid state diodes without any capacitors across them or a switching mode power supply. The source could be any piece of electronic equipment close to the TV.

Things to try:
As an experiment, try a direct connection.
Unplug everything anywhere near the TV and see if the problem goes away.
Move the player, modulator and TV to another part of the house and see if you have the same problem.
Move everything to the garage and see if it works there.

Note that you have to unplug equipment to eliminate the possibility that it is radiating an interfering signal. For a lot of stuff the power switch does not shut down the power supply.

Also, if you are transmitting on a low frequency such as channel 3, try switching to a higher frequency such as channel 13. Power supply generated interference falls off quickly with increasing frequency.

Tom,

I have to do battle with the IRS this morning. Not looking forward to that

After that is out of the way, I will try lots of changes. I am using a little Sony Watchman right now because "It Just Works" and then, I can use the vintage televisions. The Watchman is kinda like a meter because it is stable and if it works, the vintage TVs should work. That way, one is not chasing his/her tail for a generic problem.

I should have a report later today. Should be interesting. I now have four modulators and two more on the way. I guess that I want to build a rack and put my rack mount stuff all together when I move to Florida...

Looks like this may turn out to be similar to hum experienced with low power home AM transmitters. This can be very sensitive to all kinds of things in the house wiring, nearby devices, etc. I'll be interested to find out what really helps.

It seems that your video is flagged as private ?

OK, my AM60-450 is fixed. I tried using an upper channel, channel 12. Same problem. So I took it apart and found two 2200 µFD @ 35 VDC electrolytic capacitors on the power board. They measured high with the ESR meter, 5.1Ω and 8.0Ω. I didn't know if that was too high, I was looking for more like an open. So I got two brand new 2200 µFD @ 40 VDC out of my stock and replaced them. That fixed the problem. Now, it is a very clear picture. And the audio was never bad on mine either.

I would suspect that was the reason this modulator was removed from service and sold as surplus. Easy fix. I had gotten the capacitors from Mouser for another project. But I always buy about double of what I need just in case.a This time it worked!

Most or all of these modulators have three-prong, grounded power cords. The typical video source used at home does not (set-top tuner, DVD player). Try using the modulator with one of the three-to-two-prong grounding adapters (without the ground connected) and see if the hum bars go away. Then, you will know for sure if it is a ground-loop problem. I think I had this problem in the past as well.

Yes, I guess it was, I thought that meant I could share the link here and you could see it but apparently not.

Anyway I changed it to public so it should work now.

The set in the video is the 53 Philco I posted about on VK.

Nice, I'll have to look into that on mine.

I also bought a Pico Mafcom brand modulator and it barely works at all.

Inside I see a resistor on the PS that has been hot and the 30v supply is running at 26 and the 24v is at 19v so I wonder if it needs recapped too?

These probably ran 24/7 for years, not surprising they need some attention.

I'll also try hooking it up without the ground connection on teh Madulator and see if that helps.

New caps are probably a good idea in any case if it's going to be plugged in all the time.

Small price to pay. New caps are very, very inexpensive now. I think I should maybe go into my other modulators as well and replace those caps. What I did find was that the two mods that I just got most likely won't be of use to me. But they cost a whole $0.99 for the pair. Most likely will have good parts. They seem to be cable channels...

This is an old topic, but I experienced the same hum lines from my BT AM60-550A modulator and it had bugged me ever since I set it up. I know that the signal from my modulator was clean because connecting directly to a TV gives a gorgeous picture. I'm currently using Channel 3 because the signal seems better on lower channels.

Switching to a higher channel didn't cure the issue, nor did plugging in the modulator using a 2-prong adapter plug with its 3-prong plug.

The modulator was originally located near to my office desk, where interference abounds from things like my computer, cable modem, wireless router, wireless phone base, etc. Moving it across the office (farther from those things) didn't help.

What did help was running my rabbit ear antenna completely out of the room on on 20 feet of coax. With the antenna sitting in a quiet spot away from power cords & outlets, no lines are visible.

In the course of moving the antenna hither and yon, and walking around the house with a handheld TV, I noticed that antenna orientation (both transmitter and receiver) made a big difference when the lines were present, so if space is limited, simply reorienting your antennas may help somewhat.

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