Scrolling bars using agile modulator

[bigaudioal]

Originally Posted by bandersen

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"

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.

[bandersen]

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.

[Phil Nelson]

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

[wa2ise]

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.!

[bandersen]

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

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.

[Phil Nelson]

Originally Posted by bandersen

Seems to me they could have made these a lot smaller

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

[bigaudioal]

We're all in modulator land!!

[bandersen]

Originally Posted by Phil Nelson

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

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

Originally Posted by bigaudioal

We're all in modulator land!!

Indeed! Here are the insides of the BAVM-z model.

[IsthmusTV]

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.

[kvflyer]

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.

[bigaudioal]

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.

[Down Under]

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.

[bigaudioal]

Originally Posted by Down Under

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.

[DavGoodlin]

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.