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Intellivision II AV Mod Lots of Interference

Intellivision INTV

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#26 SlowCoder OFFLINE  

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Posted Tue Apr 24, 2012 8:32 AM

The reported fact that removing the RF modulator from an INTV II prevents the A/V mod from working caught my attention, so I dug into schematics. The video signal is created by a network of resistors connected to the AY-3-8915 and then travels through a diode (CR4) to the RF modulator. This diode MUST have DC current flowing through it, otherwise the video signal will be blocked. Studying the schematics reveals that the only possible source of this DC current is the RF modulator. Either disconnecting the video signal from the RF modulator or completely removing the RF modulator will thus remove this DC current, resulting in NO video signal to the A/V mod. To get the video signal to the A/V mod in an INTV II without the RF modulator, a new source for this DC current must be created. One possibility is to copy the INTV I circuitry - add a 3.3Kohm resistor between the video signal and +5V (The INTV I actually has 2 resistors in series with a diode, but all that's needed for the INTV II is one resistor with a value of 3.3Kohms.).

Thanks! I will give this a try when I get home :)


It's too bad it didn't work. Can you take a pic of the modification and post it?

#27 NS7D OFFLINE  

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Posted Tue Apr 24, 2012 10:23 AM

The reported fact that removing the RF modulator from an INTV II prevents the A/V mod from working caught my attention, so I dug into schematics. The video signal is created by a network of resistors connected to the AY-3-8915 and then travels through a diode (CR4) to the RF modulator. This diode MUST have DC current flowing through it, otherwise the video signal will be blocked. Studying the schematics reveals that the only possible source of this DC current is the RF modulator. Either disconnecting the video signal from the RF modulator or completely removing the RF modulator will thus remove this DC current, resulting in NO video signal to the A/V mod. To get the video signal to the A/V mod in an INTV II without the RF modulator, a new source for this DC current must be created. One possibility is to copy the INTV I circuitry - add a 3.3Kohm resistor between the video signal and +5V (The INTV I actually has 2 resistors in series with a diode, but all that's needed for the INTV II is one resistor with a value of 3.3Kohms.).

Thanks! I will give this a try when I get home :)


It's too bad it didn't work. Can you take a pic of the modification and post it?

I haven't actually done the modification, just figured out what would be necessary to forward bias CR4 to permit the video signal to get to the A/V mod. The 3.3Kohm resistor needs to be between the original video signal of the INTV II and +5V for this to possibly work (DC path). If installed properly, the DC voltage at the original INTV II video signal should be between 2 and 2.5 volts.

#28 5-11under ONLINE  

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Posted Tue Apr 24, 2012 3:23 PM


The reported fact that removing the RF modulator from an INTV II prevents the A/V mod from working caught my attention, so I dug into schematics. The video signal is created by a network of resistors connected to the AY-3-8915 and then travels through a diode (CR4) to the RF modulator. This diode MUST have DC current flowing through it, otherwise the video signal will be blocked. Studying the schematics reveals that the only possible source of this DC current is the RF modulator. Either disconnecting the video signal from the RF modulator or completely removing the RF modulator will thus remove this DC current, resulting in NO video signal to the A/V mod. To get the video signal to the A/V mod in an INTV II without the RF modulator, a new source for this DC current must be created. One possibility is to copy the INTV I circuitry - add a 3.3Kohm resistor between the video signal and +5V (The INTV I actually has 2 resistors in series with a diode, but all that's needed for the INTV II is one resistor with a value of 3.3Kohms.).

Thanks! I will give this a try when I get home :)


It's too bad it didn't work. Can you take a pic of the modification and post it?

I haven't actually done the modification, just figured out what would be necessary to forward bias CR4 to permit the video signal to get to the A/V mod. The 3.3Kohm resistor needs to be between the original video signal of the INTV II and +5V for this to possibly work (DC path). If installed properly, the DC voltage at the original INTV II video signal should be between 2 and 2.5 volts.

Maybe try a 10K pot... in series with a ~1K fixed resistor (just in case).

#29 ApolloBoy OFFLINE  

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Posted Wed Apr 25, 2012 2:25 PM

I wonder if there's anyone out there who'd be willing to design a new AV mod for the INTV, both of the mods I tried didn't work for whatever reason and they seemed needlessly complicated. Has anyone tried using a THS7314 or something similar with the INTV?

#30 PacManPlus OFFLINE  

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Posted Sat Apr 28, 2012 8:48 AM

Hey Guys:

There's something else wrong. The RF box doesn't work either. Something must have happened to the video circuit at some point along the mod. I'm kind of bummed, because this is my original unit from when it first came out. :(
It sucks because I've done quite a few mods on different systems myself, and as some of you know I make carts as well. So I'm not exactly new to this.

Thanks,
Bob

#31 PacManPlus OFFLINE  

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Posted Wed May 2, 2012 7:55 PM

Hi guys:

Not being one to let things go, I removed the RF modulator again (being that it didn't help - I don't completely believe it is the correct one for the Intellivision *II*)
Here are two pictures of my mod. I measured the voltage, and I am getting 2.23 Volts... but no picture.

Bob

Attached Thumbnails

  • DSCN0851.JPG
  • DSCN0852.JPG


#32 pimpmaul69 OFFLINE  

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Posted Fri May 4, 2012 9:53 PM

Hi guys:

Not being one to let things go, I removed the RF modulator again (being that it didn't help - I don't completely believe it is the correct one for the Intellivision *II*)
Here are two pictures of my mod. I measured the voltage, and I am getting 2.23 Volts... but no picture.

Bob

Looking at your mod it looks like you did a nice job. Only question i have is what size caps are u using. They are huge so i am assuming they are all high uf caps. I dont think all the caps are supposed to be that high. I think most of them were supposed to be like 10-100 uf

Edit: also if the caps are the correct size, strangely enough with audio and video the physical size of caps can make a difference. Smaller size caps can provide more power.

Edited by pimpmaul69, Fri May 4, 2012 9:59 PM.


#33 PacManPlus OFFLINE  

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Posted Sat May 12, 2012 5:29 PM

Hi!

@pimpmaul69: Thanks! They are 100uf like the instructions called for. I'll try to find shorter caps.


UPDATE:
I bought a new board from someone here on AA for $12 (+$8 shipping) so my old INTV II is back in business.
Now - again, not being one to give up, I re-wired my old board (now, not being afraid of burning it out). The TV I have it on (I no longer have any tube TVs in the house :( ) is one of those that give a black screen and says 'No Signal' when it the signal isn't "strong enough" (I wish there was a way to disable that).

Now, I get that message, intermingled with a scrambled picture (see screenshots). So I *AM* getting a signal, but it's not strong enough? :?

Can anyone tell from the pics what's going on? (BTW, I'm using the 'Demonstration Cartridge' that they used to use in the kiosks to test with because it runs constantly)
That particular screen actually is blue and if you click on the first pic, you can see letters.
I am pretty good with electronics, but I have no clue what's going on here.

DSCN0853.JPG

DSCN0854.JPG

Thanks,
Bob

#34 PacManPlus OFFLINE  

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Posted Sun May 13, 2012 12:58 PM

Hi again, guys:

I am sorry for derailing the thread again, but maybe fixing this may help the OP.

I found out something. The 3.3K resistor is not the right value. As I dropped the resistor value, more of the screen showed intermittently before alternating with 'No Signal'. I tried 2K, the screen came is a little better. I tried 1K, it came in even better, but still not stable.
Then I tried 330ohm, and the results looked similar to the 1K resistor. I dropped down to 10ohm and got nothing again. So I *think* the real value is somewhere between 0-1K I need to find a variable resistor with that range of values because this is very time consuming. :(

If we can figure this out, we then have a good video mod that doesn't require the RF modulator. :)

Thanks guys,
Bob

#35 PacManPlus OFFLINE  

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Posted Mon May 14, 2012 6:01 PM

Hi again, Guys:

Here is a video I took of the screen and a close up of the modification. If anyone knows what is going on, I would appreciate it (and I think the OP would too - maybe he can remove the RF box and get a cleaner picture)


Thanks,
Bob

#36 flammingcowz OFFLINE  

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Posted Mon May 14, 2012 6:13 PM

It might just be the TV. I had an AV modded atari that wouldn't work on any HDTV in my house. On some it would roll the picture and on some wouldn't register at all. On a good old CRT though it was perfect. Try taking to someones house that has one, or even get a cheap one on craigslist.

#37 PacManPlus OFFLINE  

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Posted Mon May 14, 2012 6:21 PM

Thanks, but all of my other A/V Mods (multiple 7800s, 2600, Stunt Cycle) work great on this TV... Unless the INTV gives some strange signal that the others don't. :(

#38 5-11under ONLINE  

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Posted Mon May 14, 2012 6:24 PM

Can somebody post a link to schematics for the Intellivision 1 and or 2, ideally including the RF modulator? This might help.

#39 flammingcowz OFFLINE  

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Posted Mon May 14, 2012 6:34 PM

I know the INTV 1 stock output is very good. It looks like it has already been modded, but it also has an insane amount of RF shielding. Is the INTV 2 the same way, or is its stock output a lot worse than the first INTV?

#40 PacManPlus OFFLINE  

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Posted Wed May 16, 2012 1:45 PM

Here are the schematics for the INTV II (although they are a little hard to read): http://console5.com/...ntellivision_II

At the bottom of the page, there are links to the actua schematics and the data sheet to the RF modulator.

Hope this helps, and thanks,
Bob

#41 PacManPlus OFFLINE  

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Posted Fri May 18, 2012 6:16 PM

Ok guys - nevermind. I tossed the board.

I've learned not to A/V my INTV II - it doesn't work.

Bob

#42 cmart604 OFFLINE  

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Posted Fri May 18, 2012 8:06 PM

Ok guys - nevermind. I tossed the board.

I've learned not to A/V my INTV II - it doesn't work.

Bob


Bob, let me know if you need another INTV2, I'm pretty sure I can come up with one as thanks for making so many awesome 7800 games.....and maybe as bribery to consider an INTV release or two? :)

#43 PacManPlus OFFLINE  

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Posted Sat May 19, 2012 6:16 AM

Thanks, man - I already have another board (which is why I wasn't afraid to toss this one).

I appreciate the offer! :)
Bob

#44 RangerG OFFLINE  

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Posted Mon Oct 20, 2014 4:14 PM

If you have an A/V modded INTV II, can you use the System Changer? Will the System Changer use the new a/v or the old rf?



#45 pimpmaul69 OFFLINE  

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Posted Mon Oct 20, 2014 9:24 PM

If you have an A/V modded INTV II, can you use the System Changer? Will the System Changer use the new a/v or the old rf?

no




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