TV adapter question.

Hardware questions and modifications

TV adapter question.

Postby Corey986 » Sat Dec 20, 2014 9:14 am

Is there any quality difference between using the IBM TV adapter and using a standalone 3rd party modulator with the composite video?

I'm setting up a Jr with a Vintage TV.

Thanks,
Corey
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Re: TV adapter question.

Postby Brutman » Sat Dec 20, 2014 9:52 am

I think the official adapter also carries sound from the PCjr. Avoid using an RF adapter for anything if you can use composite instead - composite is far better.
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Re: TV adapter question.

Postby Corey986 » Sat Dec 20, 2014 4:33 pm

When I use composite straight to the TV, it has a hard time locking on to the signal. Are there any signal adjustments for the PCJr for signal strength?

Thanks,
Corey
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Re: TV adapter question.

Postby Brutman » Sat Dec 20, 2014 7:46 pm

When you say "hard time locking onto the signal", can you describe it in more detail?

There is nothing strange about the signal from the PCjr, and nothing really adjustable either. It wants a bog standard cable with 75 Ohms impedance and low capacitance. Try a different cable, and make sure it's nice - that might help.

It's possible that the Jr is out of spec. If the machine is running well then the video should be running well too - all of the timings derive from the system clock.
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Re: TV adapter question.

Postby Trixter » Sat Dec 20, 2014 11:09 pm

Brutman wrote:all of the timings derive from the system clock.


Something to note if you have an enhanced PCjr (ie. with a speed modification).

As a test, I just now connected a random PCjr to my 55" 4-yr-old Visio HDTV and it displays fine.
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Re: TV adapter question.

Postby jmetal88 » Sat Dec 20, 2014 11:14 pm

Trixter wrote:
Brutman wrote:all of the timings derive from the system clock.


Something to note if you have an enhanced PCjr (ie. with a speed modification).

As a test, I just now connected a random PCjr to my 55" 4-yr-old Visio HDTV and it displays fine.


A properly done speed modification increases the clock speed to the CPU without increasing the clock speed to the rest of the system. That's why the instructions for the SpeedUp modification have you piggyback a new clock generator on top of the old one rather than just swap out the crystal.
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Re: TV adapter question.

Postby Brutman » Sun Dec 21, 2014 12:00 am

Besides the fact that just swapping crystals does not work at all on a PCjr for many reasons ...
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Re: TV adapter question.

Postby Trixter » Sun Dec 21, 2014 11:13 am

I stand corrected!
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Re: TV adapter question.

Postby Corey986 » Sun Dec 21, 2014 1:08 pm

I swapped out the video line with a different one and all is good on composite. The weird thing is I have used this same cable on the same TV with my Apple II, various Apple-1 and both my Sol-20 and no issue. Granted the only color one is the Apple II, but it's a rev-0 so the video is way off NTSC. I guess the signal strength on the Jr is lower than the other machines which are all 6+ years older. Maybe they had to lower the signal for FCC reasons in the 80's. I'm just happy problem solved.

Now to find and hack up a DOS 5 disk so I can use the full capacity of my JRIDE as a single drive.

Cheers,
Corey
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Re: TV adapter question.

Postby Brutman » Sun Dec 21, 2014 5:50 pm

Cables go bad more often that people realize. And the cable might have been marginal even when it was manufactured. This goes for any type of cable; when it doubt, try another. I'll bet that you'll find the resistance on that cable is fairly high.

There is nothing oddball about the PCjr - the composite video signal is pretty well standardized.

You have an Apple 1 you say?


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