Author Topic: Intellivision AV Mod Problems identified  (Read 1977 times)

Offline retromod

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Intellivision AV Mod Problems identified
« on: January 16, 2014, 09:30:58 AM »
After some days of Intellivision reverse engineering I finally found a suitable solution to fix the ugly AV mod problems and it is now sharp, has much less noise etc. 

As seen within the youtube video regarding the TUT tutorial the Intellivision delivers first hand a really good and sharp picture out of it's video logic. But the video clearly shows (and this was not mentioned at all in the long installation guide but obvious recognized by many people within several threads) the output contains noise/interferance from power supply and HF modulator. 

If you disable the HF modulator by adding a switch to the 12V power line you'll get much less noise but the picture is awfull despite that. Other approaches replaces the HF modulator completely or offer an additional circuit to work around but do not fix it.

It suffer from:

1. bleeding and highlighting of areas which are in contrast (best modul for testing: frog bog)
2. moving/rolling pixels (frog bog, Donkey Kong: building)
3. washed and unsharp areas due to the noisy lines (best viewable if you reduce the brightness dramatically then you will notice lines are moving from top to bottom).

Analysis:

problem #1: this is purely a problem of the Intellivision design, it seems the onboard components changes values if it heats up (specially after several hours the picture gets worser and worser within minutes). The onboard regulator has a too short range so 1000th inch move decides if good or bad picture there is nothing between.

problem #2: is due to the nature of AV/composite and the only way to get rid of it is to use another output format (like RGB,S-Video) or a clamp filter. Using AV always leads to borders across areas that's by design due to mix of signals. This rolling is most likely due to luminance signal range moving into chroma range.

problem #3: GND and power supply problem. Too much noise from given pin locations.

I've verified all kind of standard video amplifier (all mods are nearly based on the same circuits and concepts) and it seems it doesn't care which one you are using. Sometimes you'll get a better less noisy picture but even that picture is too bad in comparison with other consoles. After some tests it pointed out the Intellivision video signal is soo good that is doesn't really required a big video amplifier or conversion, even a few resistors are sufficient. The picture is always sharp, colorful and much better than any other consoles like Atari or Coleco Vision. The picture has too much contrast and reducing it leads to noisy lines. But the mod requires a switch to allow justification of brightness.

So first approach was to disable the 12V line on the HF modulator. Noise was now a little bit better. But as good modders never every breaks anything (design nor functionality) I reversed the change. Finally I moved the AV solder point according to the schematics and now it doesn't care if the HF modulator is on or off, there is no difference in signal anymore and old HF modulator still works.

I also re-arranged the locations of the ground and power solder points and picture increased dramatically in output. The noise is still there but less visible. The added brightness switch on the mod was set to ~80% (you will notice picture gets quite clear and very good until it immediately drops to old quality if you move the switch too far). And of course it is important how the motherboard switch is set. It seems it is fairly overdriven in its possibities so replacing it with a finer one saves a lot of time in adjustment. The old one requires to adjust within 1000th of an inch to get the best picture out of it and still allows to detect the video signal - else if it is on a wrong position there is no picture at all or it fades away after a while.

Now the picture is as good as on other consoles. Frog Bog is playable now and Donkey Kong or Deamon Attack has very good picture similar to the RGB mod output (sure the AV limitations are visibile).

To address that i've tried to get a FMS6141 up and running to filter the picture a little bit but finally it failed because it is unclear where this IC comes from and if it is still working or simple dead. I've tried to find a video filter with clamp filter integrated to get rid of problem #2 but it seems there are less products on the market these days. As S-Video is nearly dead from TV set producers point of view the IC production was also cancelled for all kind of components. Bad because these chips also contains composite features so it is quite hard getting anything suitable to do the job. If someone has a hint regarding such a filter let me know.

PS: I've altered the PCB layout using my own Video Amplifier (which is completely different to the standard one but less complex) and together with the Stereo Surround Mod it fits on a 1" by 2" PCB providing the best sound and picture experience ever on Intelllivision (not seen the output of RGB yet but as the instruction uses the same solder points as AV I assume it suffer from similar issues than problem #3).
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Offline zapiy

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Re: Intellivision AV Mod Problems identified
« Reply #1 on: January 16, 2014, 10:07:49 AM »
Fantastic work fella, whats the work involved like for people that might want to do the same? Is it best left to a pro or could anyone manage it?
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Offline retromod

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Re: Intellivision AV Mod Problems identified
« Reply #2 on: January 16, 2014, 10:24:55 AM »
Quote from: "zapiy"
Fantastic work fella, whats the work involved like for people that might want to do the same? Is it best left to a pro or could anyone manage it?

well from description anyone familiar with electronic is able to do it even if there are missing details like right solder points etc. From schematic it is quite clear how to implement. if you do it wrong you may destroy any component as you dig deeper into the PCB layout not really using existing solder points as given by HF modulator based mods.   

I will not offer a step by step instruction due to my bad experiences. 

Attached samples of the output. These were made with a handy camera in front of a plasma TV (about 1 meter). So the brightness is expected and less on other TV systems. You will not notice any flickering anymore if you are 1-2 meters away from screen. Previously it was visible even 5 meters away! Not sure why people demonstrate their mods with tube TV's as the output looks always better than on other TV sets. There was no altering/filter activated so picture is 1:1 from input source.
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Offline zapiy

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Re: Intellivision AV Mod Problems identified
« Reply #3 on: January 16, 2014, 10:39:22 AM »
Thats a fair point actually.. I am a electrical engineer by trade so soldering is second nature to me but i guess others may struggle and put there beloved machine way past repair.
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Offline retromod

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Re: Intellivision AV Mod Problems identified
« Reply #4 on: January 17, 2014, 08:26:17 AM »
I've added some pictures. Another idea is to add a switch to allow old video solder point from HF modulator AND new one. Reason is that new mod is using a solder spot prior to mixed signal and extensions using own video sources like Atari 2600 modul may not properly shown as signal is mixed far behind that spot.

On the other side the HF modulator is still working so those people may use the HF modulator in such cases. What are you thinking about? Required or do most people not own the Atari 2600 modul or similar extensions? If using such extensions the video signal is much better even from HF video solder point because only the signal coming from video unit of the mainboard is noisy. If adding a switch those extensions are shown with good quality but without the quality is on old AV-mod level.
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Offline zapiy

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Re: Intellivision AV Mod Problems identified
« Reply #5 on: January 17, 2014, 08:55:07 AM »
That's a good idea but I have no idea if it's a worthwhile idea.  Others here would be better placed to answer that question.
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Offline retromod

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Re: Intellivision AV Mod Problems identified
« Reply #6 on: January 17, 2014, 09:06:18 AM »
it requires an additional cable plus switch, that's it. About 1 eur. so not a big task.
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Offline retromod

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Re: Intellivision AV Mod Problems identified
« Reply #7 on: February 03, 2014, 11:48:15 AM »
It seems the pot on the board has the wrong dimension leading to difficulties during adjustment. If you move too far the picture get worse, if it is in right position (which could be 1/100 inch movement) the picture is crystal clear.
So the only way to improve that is to replace the pot with a finer one, which requires some additional components as pot's are not available in any starting/ending range.

Finding the right position requires up to one hour but picture is then equal to RGB output.

A suitable replacement for the switch was found and requires some testings. If this is successful I will enhance the existing PCB (AV and stereo) with Atari Joystick ports, too. So having one PCB to drive the Intellivision to it's limits in video, audio and game experience....
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Offline retromod

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Re: Intellivision AV Mod Problems identified
« Reply #8 on: April 11, 2014, 10:19:24 AM »
Hopefully I will find some time to implement some additional enhancements to this mod. An all-in-one solution as done for Atari and Coleco devices is on the agenda.

So having one PCB with Joystick ports (atari style), backlight control, improved AV and latest stereo surround (3D Audio, noise reduction) is in planning. Stock is full of intellivisions waiting for this circuit.
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Offline retromod

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Re: Intellivision AV Mod Problems identified
« Reply #9 on: June 25, 2014, 13:19:51 PM »
Finally all problems are solved with the new Intellivision AV Plus mod. It allows to keep the HF modulator, output a great picture which is compliant to all TV sets and there is no ghosting and noise anymore. Typical composite issues are now gone on modern tv sets.
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Offline retromod

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Re: Intellivision AV Mod Problems identified
« Reply #10 on: July 25, 2014, 14:00:41 PM »
After some mods it seems there are a bunch of Intellivision 2609 consoles suffering from a design issue. You may notice the following issues on them:

1. inserting a cartridge and switching on the TV does not lead to a picture until you push "RESET"
2. the video output of a mod is worse getting better or gets worser after a while.

both indicates a design flaw. It seems that specially on PAL consoles the layout was altered to honor the PAL requirements. the console gets very hot after a while and influences the components which starts to fade away from it's optimal values. So the AV Plus mod works great and after a while the picture seems to "swim" or it looks ugly in the first run and gets better and better within minutes. The mod does not show any color crowling anymore as seen on the normal mods available at other websites (until these types of consoles gets hot or cool down).

I've messured the video signal and it is great leaving the video processor but will be polluted entering the LM1886/LM1889 chipset or quartz. So any attempt using a better power supply, using a filter amp etc will fail.
the chroma signal generated by the LM chipset is far beyond specification and does not require any further amp but the luma signal is quite weak. Even splitting them up doesn't help as the logic inside the console fades away from correct values due to temperature.

So this requires additional work getting out the heat and/or moving the components. I will start some testings to get more experience which component is responsible for the value drift (most likely the quartz). On the RGB mod the LM chipset is bypassed/removed so the noise may not be seen. But there is only limited information about the mod and quality and as always CRT pictures are presented which are not so bad due to technical limitations. So stabilizing the temperature or protecting some components may solve this issue. Unclear what kind of Intellivision version is affected because not all of them suffer from temperature.

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Offline zapiy

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Re: Intellivision AV Mod Problems identified
« Reply #11 on: July 25, 2014, 22:01:35 PM »
Nice discovery, i take it most older systems suffer this way.
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Offline retromod

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Re: Intellivision AV Mod Problems identified
« Reply #12 on: November 17, 2014, 09:56:30 AM »
It seems several people noticed that the standard AV mod is crappy starting with modern TV sets. So beside the possibility using sun glasses all the time during gaming I try soon to evaluate the possible solution pathes:

1. get the signal as early as possible and move whole circuit location outside of heated area

or

2. use some kind of autoadjustment so if heating influences the mainboard values it automatically adjusts the circuit values as well.

or

3. cool down system (which is quite difficulty due to it's implementation and limited space).
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