Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Nov Sun 29, 2020 6:29 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 6 posts ] 
Author Message
 Post subject: Blonder-Tongue AM-60 550B "wobbly" picture and weak output?
PostPosted: Dec Fri 14, 2018 4:07 pm 
Member

Joined: Jan Thu 11, 2007 2:23 am
Posts: 583
Location: Maumee, OH
Hi all, I purchased this agile modulator on eBay sometime last year, and it worked great for quite a while, but eventually stopped working after running for long periods of time. I suspected it was getting a little too warm and also needed some power supply caps. Fast-forward several months later, I replaced all the power supply caps (last night!) and hooked it back up.

Before the repair, I had it hooked up to a homemade dipole antenna cut to the correct lengths and could pick up my broadcast on channel 12 upstairs pretty well, as well as on the broadcast-only black and white set I have downstairs about 15 feet from the modulator.

Now, I can pick up the signal pretty well from the B&W set, but the picture can only be described as somewhat "wobbly"; the bottom of the image kind of vibrates up and down, distorting the whole image ever so slightly. It seems to be a 60 Hz related problem, but it doesn't change no matter where I put the antenna. The antenna itself is as far as it can be from electrical wiring (which is admittedly not too far), and is parallel with the wiring that it is somewhat near, so actual RF interference is minimized. I am also unable to get my flat screen TV upstairs to pick up the channel at all; I've tried auto-scanning and searching for that particular channel individually, but it never turns it up. (Stupid digital TV won't let me add a channel manually; it won't add it if it doesn't "see" it.) My upstairs antenna hasn't moved from where it was before when the modulator previously worked, and I even tried moving it closer to the modulator, to no avail.

Note that I was somewhat unsure of where to connect the power supply wire for the Phillips BGY585A amplifier directly connected to the RF output of the modulator when I reassembled it; the wire was just wrapped around a post on the power supply, and I saw several voltages present: one post marked both +18V and +20V; another marked +30V; and some others that didn't seem to be relevant because the wire wouldn't reach them anyway. I read the spec sheet on the Phillips unit, and it mentioned a Vb of +24V, so I tried both the +18/+20 post and the +30 post, but the results were the same, so I left it on the +18/+20 post to be safe.

I'm thinking there's something else wrong with the modulator itself, but I'm not sure what. Anyone have other thoughts on what to check? I suppose I could just pick another one up on eBay but I'd rather try to fix the one I have if possible.

Thanks!


Top
 Profile  
 
 Post subject: Re: Blonder-Tongue AM-60 550B "wobbly" picture and weak outp
PostPosted: Dec Fri 14, 2018 7:24 pm 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 2644
Location: Dallas, TX
pianoman wrote:

Note that I was somewhat unsure of where to connect the power supply wire for the Phillips BGY585A amplifier directly connected to the RF output of the modulator when I reassembled it; the wire was just wrapped around a post on the power supply, and I saw several voltages present: one post marked both +18V and +20V; another marked +30V; and some others that didn't seem to be relevant because the wire wouldn't reach them anyway. I read the spec sheet on the Phillips unit, and it mentioned a Vb of +24V, so I tried both the +18/+20 post and the +30 post, but the results were the same, so I left it on the +18/+20 post to be safe.

Thanks!

I suppose the +18/+-20 post was correct. You should take better notes when you take something apart. Those modules can be blown easily. Did you measure all the voltages?

_________________
Tim
It's not the Destination, It's the Journey.


Top
 Profile  
 
 Post subject: Re: Blonder-Tongue AM-60 550B "wobbly" picture and weak outp
PostPosted: Dec Fri 14, 2018 8:36 pm 
Member

Joined: Jan Thu 11, 2007 2:23 am
Posts: 583
Location: Maumee, OH
Notimetolooz wrote:
pianoman wrote:

Note that I was somewhat unsure of where to connect the power supply wire for the Phillips BGY585A amplifier directly connected to the RF output of the modulator when I reassembled it; the wire was just wrapped around a post on the power supply, and I saw several voltages present: one post marked both +18V and +20V; another marked +30V; and some others that didn't seem to be relevant because the wire wouldn't reach them anyway. I read the spec sheet on the Phillips unit, and it mentioned a Vb of +24V, so I tried both the +18/+20 post and the +30 post, but the results were the same, so I left it on the +18/+20 post to be safe.

Thanks!

I suppose the +18/+-20 post was correct. You should take better notes when you take something apart. Those modules can be blown easily. Did you measure all the voltages?


Yeah I can't believe I didn't take a note of that when I took this thing apart, that was definitely a mistake on my part.

I haven't had time yet to take all 15 screws off the top again and measure voltages but it's on my bench ready to go when I do. I did find that the output is not actually weak; I took the B&W TV upstairs and it still worked just as well as it did downstairs, so I'm guessing the flatscreen TV isn't happy about the "wobbly" output or something.


Top
 Profile  
 
 Post subject: Re: Blonder-Tongue AM-60 550B "wobbly" picture and weak outp
PostPosted: Dec Sat 15, 2018 6:05 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2907
Location: WI 54812
Have you tried connecting the BT 75 ohm output directly through a balun to an older sets antenna input? That way you'll eliminate external 60hz sources hitching a ride. This should give you a baseline for further troubleshooting. You may need to turn down the BT output signal level to eliminate overloading the sets AGC.


Top
 Profile  
 
 Post subject: Re: Blonder-Tongue AM-60 550B "wobbly" picture and weak outp
PostPosted: Dec Mon 17, 2018 5:48 pm 
Member

Joined: Jan Thu 11, 2007 2:23 am
Posts: 583
Location: Maumee, OH
Kevin Kuehn wrote:
Have you tried connecting the BT 75 ohm output directly through a balun to an older sets antenna input? That way you'll eliminate external 60hz sources hitching a ride. This should give you a baseline for further troubleshooting. You may need to turn down the BT output signal level to eliminate overloading the sets AGC.


Thanks, good idea! I'll give that a shot as soon as I find a 75 ohm patch cable I can cut down for testing. I may have purged all my spares during some recent spring cleaning...


Top
 Profile  
 
 Post subject: Re: Blonder-Tongue AM-60 550B "wobbly" picture and weak outp
PostPosted: Dec Sun 23, 2018 3:39 am 
Member

Joined: Feb Fri 20, 2015 10:37 pm
Posts: 161
Location: SE Minnesota 55949
Not related to fixing your BT, but try scanning channels on your digital TV while the BT is on and it should pick up your channel 12, if it accepts analog channels. The signal will be there then.


Top
 Profile  
 
Post New Topic Post Reply  [ 6 posts ]  Moderators: Mr. Detrola, 7jp4-guy

All times are UTC [ DST ]


Who is online

Users browsing this forum: philsoldradios and 6 guests



Search for:
Jump to:  




































Privacy Policy :: Powered by phpBB