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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Mon 09, 2021 9:41 pm 
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Joined: Apr Sat 06, 2013 2:18 pm
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Location: New Hampshire
When you try the DVD do you see ANY activity or audio ?

If you have an old working VCR try that. It wont work right but it will work.

Try the VCR in RF first on ch3 or4. If that works try the composite outputs, RCA jacks &
the modulator. That will prove out the problem.

BTW some but not many DVD's did have an RF modulator built in. EVERY one I have seen
had composite outputs. But thats up to abt 10 yrs ago.....

Try that first but DONT mess with the tuner yet , other than the fine tune knob.
You can bleep that up easily.

If need be will give a quickie tuner lesson :D

73 Zeno 8)


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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Wed 11, 2021 9:49 pm 
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Joined: Feb Thu 18, 2021 3:09 pm
Posts: 118
New tuner tubes came in as well as video if amp tubes. Made no difference. That's upsetting. This is so strange. Tried another dvd player as well and 2 different RF modulators. Nothing.


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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Wed 11, 2021 9:54 pm 
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Joined: Feb Thu 18, 2021 3:09 pm
Posts: 118
zeno wrote:
When you try the DVD do you see ANY activity or audio ?

If you have an old working VCR try that. It wont work right but it will work.

Try the VCR in RF first on ch3 or4. If that works try the composite outputs, RCA jacks &
the modulator. That will prove out the problem.

BTW some but not many DVD's did have an RF modulator built in. EVERY one I have seen
had composite outputs. But thats up to abt 10 yrs ago.....

Try that first but DONT mess with the tuner yet , other than the fine tune knob.
You can bleep that up easily.

If need be will give a quickie tuner lesson :D

73 Zeno 8)



Thanks! I need to go get my VCR from my office. Both DVD players I tried have an RF modulator in them. I have messed with the tuner in terms of the coils inside or anything like that. Strange that the pattern generator gives a perfect image and yet I can't get any audio or video from two DVD players.


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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Thu 12, 2021 2:29 am 
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Location: Chicago, IL USA
It's not just strange, it's not possible. Can we see a photo of the back of the DVD player and how it is hooked up to the TV ? Have you checked you cables and any adapters for continuity ?


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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Thu 12, 2021 2:50 pm 
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bandersen wrote:
It's not just strange, it's not possible. Can we see a photo of the back of the DVD player and how it is hooked up to the TV ? Have you checked you cables and any adapters for continuity ?


Here is the back of the DVD player. I hookup coax to tv. I've tried multiple coax cables. Attached is a video of this setup playing on my Zenith set. Nice picture. On the Predicta, I get nothing. Is it possible the Predicta isn't picking up the signal too well? I replaced the rf amp and mixer tube in the tuner.


Attachments:
Screen Shot 2021-08-12 at 9.47.39 AM.png
Screen Shot 2021-08-12 at 9.47.39 AM.png [ 784.88 KiB | Viewed 1311 times ]

[ Play Quicktime file ] IMG_1936.mp4 [ 4.17 MiB | Viewed 1311 times ]
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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Thu 12, 2021 3:34 pm 
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OK, but how are you connecting the two ? Are you using 75 ohm coax with a 75-300 ohm balun adapter with spade terminals going to the Predicta antenna terminals ?

Also, what effect does the local / distance switch on the back of the Predicta have ? Or does this version of the chassis not have this switch ?


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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Thu 12, 2021 3:55 pm 
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Jack, do you mean you attach a cable to the threaded "OUT to TV" connector and the other end to the TV?
You should use a 75 to 300 ohm transformer (balun) between the coax cable and the Predicta's terminal.
As a matter of fact one of the differences between the 10L43 chassis and the 11L43 chassis is the local/distance switch I think.

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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Thu 12, 2021 4:30 pm 
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Yes sorry for not clarifying. I am using a 75-300 ohm attachment that goes to the spade terminals. I am using the threaded OUT to tv on the DVD player. This 11L43 chassis doesn't have the switch.


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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Thu 12, 2021 5:26 pm 
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Are you sure the Predicta is tuned to the channel the player is putting out?

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


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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Thu 12, 2021 5:46 pm 
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Notimetolooz wrote:
Are you sure the Predicta is tuned to the channel the player is putting out?


Yes, it's tuned to the right channel. I also tried every other channel and not a hint of video or audio was coming through. Just static. I tried another pattern generator and I could sort of see an image on the screen but it didn't come through as well as the B&K pattern generator


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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Thu 12, 2021 7:19 pm 
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How high do you have the output level of the B&K set ? Have you checked the IF, detector and video output tubes ?


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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Thu 12, 2021 9:35 pm 
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bandersen wrote:
How high do you have the output level of the B&K set ? Have you checked the IF, detector and video output tubes ?


I have the output level on max for the B&K set. I put in new video IF amp tubes. Tried a different 6AM8 detector and 6AW8 video output tube.


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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Fri 13, 2021 1:36 am 
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So it seems like the pattern generator works because it blasts a signal through the tuner and/or IF strip.
It is demodulated properly by the video detector. The problem would be before the video detector. it could be many things including a bad IF transformer, bad alignment, tuner problems, bad IF tube socket, resistor, etc.

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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Fri 13, 2021 3:21 am 
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Thank you Tim. You've helped me a lot of a few projects of mine. I'm going to do a deep dive into this this weekend and keep updating the progress.


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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Fri 13, 2021 4:22 am 
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Location: Belrose, NSW, Australia
If you get snow on the screen and white noise in the sound, the entire tuner and IF will certainly be OK, at least working well enough to show you a picture if the correct frequency is arriving at the antenna terminals. We already know it's OK because of the test signal from the B&K.

I still think yours is a connection issue.

I have not seen a VCR/DVD combo that outputs a DVD via the modulator, that normally only works for the VCR. Are you sure that what you are seeing on one channel or another isn't the VCR's analog TV tuner being output to the modulator? Are you sure the modulator is switched in? Many devices have a "TV/VCR" switch that switches the RF output between the modulator and the antenna. In some cases this is automatic and only kicks in when you play a tape. If you don't have such a switch it is more likely that the modulator is UHF and your Predicta doesn't tune to it.

And I assume you are not trying to use the "coax" output on the RCA connector? That is a digital audio output.

I should add that back in the day I spent many many hours on the phone trying to sort out RF modulator to TV connection issues just like yours.

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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Sat 14, 2021 1:48 am 
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^^^^^^^^^ Time to read or reread the instruction manual for your VCR/DVD player.

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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Sat 14, 2021 11:28 pm 
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Here is a most basic test, but maybe you already did this: Connect your VCR/DVD player to another TV set and confirm that it works fine on both of its channels (3 and 4 in the USA).

Also, another test: Connect your pattern generator to that same other TV set, then reduce its output until the signal goes away (if it even does go away at the minimum setting), or becomes weak/snowy. Then, increase the level just until the snow goes away. Now, without changing the level, connect it to the Predicta set again, and see how the signal looks. If the signal is weak or even not visible, then you do have a problem in the Predicta's RF/tuner or maybe IF section.

Let us know how these two tests go.

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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Sun 15, 2021 12:42 am 
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ChrisW6ATV wrote:
Here is a most basic test, but maybe you already did this: Connect your VCR/DVD player to another TV set and confirm that it works fine on both of its channels (3 and 4 in the USA).

Also, another test: Connect your pattern generator to that same other TV set, then reduce its output until the signal goes away (if it even does go away at the minimum setting), or becomes weak/snowy. Then, increase the level just until the snow goes away. Now, without changing the level, connect it to the Predicta set again, and see how the signal looks. If the signal is weak or even not visible, then you do have a problem in the Predicta's RF/tuner or maybe IF section.

Let us know how these two tests go.


Okay very smart idea with the pattern generator. I'll perform that test. I also wiggle the tuner arm and picture jumps around so I think there might be something wrong with the tuner in general. Wish I had a replacement to rule out that possibility. I'll report back on how the pattern generator turns out. I already tried another vintage set with another VCR and it showed up on there but not the Predicta.


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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Sun 15, 2021 3:35 pm 
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It's possible that the pattern generator creates one or more strong harmonics at various multiples of the intended frequency. If your Predicta's tuner is far enough off frequency, it could be receiving one of those. You could check for this by scanning through all the channels on a working TV to see if it receives the signal on any other channels.


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 Post subject: Re: Predicta Debutante Pattern Generator Works DVD player do
PostPosted: Aug Tue 17, 2021 12:00 am 
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If I'm not mistaken the person with the set is in Brittan. European VHF probably uses different channel spacings, frequencies and audio carrier offsets and the same probably goes for UHF (if the set even has that option). If you are going to use RF you'll want a North American RF modulator that is set up for the same channels as the set was made for.


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