Epoch Cassette Vision video mods

[marauder666]

The Epoch Cassette Vision and Jr. are strange beasts.

 

The circuitry in the console is little more than a -6V power supply, controller connections, and a RF modulator IC and supporting circuit, which also generates colour.  Theres no processing in the consoles, its in the cartridge.  A microcontroller which runs the game programmed into it, and generates a luma/sync video signal, and colour difference signals.  In fact hooking up a cartridge to a 3.58Mhz crystal oscillator and a -6V power supply can generate an mono image on screen without needing anything else.

 

 

GDT2019, Geoff, on the forum sent me and Juansolo a pair of these to see if we could get a composite signal out of them.  He’s had them years, and without a TV with Japanese RF tuner is out of luck, never seen them work.

 

We first started on the Jr., its much easier to work on than the original,  and managed to get a horribly corrupted screen on a UK TV using manual tuning, so we know its working to some extent.  Lots of sparkles everywhere, more on that later.

 

As the micro controller runs at -6V the luma and sync signals are inverted, so I used a MC14576 video opamp to invert it and managed to get a mono picture on screen, but its still sparkly, did some tweaks to the circuit and the sparkles will not go, they are in the luma signal, they look bad on an oscilloscope.  This is on all cartridges,  so it looks like a fault with the Jr.

 

Next to look at the colour signal, theres not much info online about these machines, but did find a pinout of the RF chip, and it does output a chroma signal, which goes back to the cartridge, some sort of feedback, as without that connected the output is just mono.  Hacked another bit of circuitry and we have a colour picture, not great, the sparkles are now blue and red, very annoying.

 

At this point we have no idea of the other console, so we remove the video mod from the Jr, and wire it into the other one, no sparkles, confirmed its a fault with the Jr.  Theres some crosstalk interference, but its not bad.   Picture is good enough on this one to support S-video, Geoff has monitors and TVs which support it so why not.

 

Made the mod much simpler by adding a FMS6400 video chip on the output to generate correct luma and chroma outputs, well, as correct as the off spec inputs will allow.  Also, it supports a composite output which works on the big console, so thats wired up too.  Not as good on the Jr, which works better with my method of just connecting the luma and chroma on the output, probably due to the sparkles causing chaos in the chip.

 

The mod is now just a pair of ICs, a few resistors and caps.  And fits easily in either console.

 

Now, its time to find a suitable PSU for these things, they are centre negative 6V 300mA, 100V.  Not much use in the UK.

I’ve been running them on a variable voltage, reversable tip transformer type one I’ve had years and it worked well, but its a big heavy brick, and it would be nicer to find something smaller.   Got a XP Power 6V, 830mA wall wart, and changed the plug to be centre negative, plugged it in, it works, but the picture has more interference than with my transformer based one.  Needs some more filtering to clean it up, added a 2200uf capacitor across the power input socket, and it looks the same as my PSU now.

 

They still have some weird issues, the big console doesnt like the Sony flat panel portable I’ve got, the colour is barely visible, the Jr with all its sparkles works.  Jr looks ok into a Sony CRT composite with the colour turned down so the background is nearly black which hides some sparkles.  Into the PVM Jr looks pretty crappy, its resolving too much of the sparkles, but the big one over S-video looks very good, just a little interference, especially on the Battle Vader cart.  Due to the way the video is generated in the cartridge, video quality varies between carts, so its all a bit of a compromise.  We mainly used Pak Pak Monster to do the testing, so this looks the best, and its the best game.  RF for all it’s faults hid these video issues.

 

Sound output is just a resistor and a cap, bearing in mind that the bias voltage is -6V, so the cap appears to be backwards. More positive  on the output side.  Thats the same with the luma signal into the MC14576.

 

 

 

Edited May 23, 2021 by marauder666

[juansolo]

 

Veroboard layout for the video mod

Edited May 23, 2021 by juansolo

[GDT2019]

Just to say gents, absolutely blown away by the amount of work the pair of you have put in on these for me.  It will be great to actually play these after having more or less just been ornaments for the last 3 or.so years of owning them (possibly longer).  Thanks really does  not cut it.  I'm hugely impressed and have enjoyed being included as you have discovered more and more about these not-so-common machines.

 

Cheers.

[marauder666]

Geoff also sent an Epoch Invader, its the same hardware but with the cartridge on the main board, so thats now modded too.  Same circuit.

 

 

[Retro_Game_Lover96]

There is a video about the video mods such as YPbPr.

 

[virtvic]

I have a TV Vader too. Any chance you’d share that video mod so I can see if mine works ok? 

[soundretroco]

Hi all, I'm attempting to perform this s-video modification in an Epoch Cassette Vision and coming up short. I've recreated the circuit as shown in the diagram   , and luma comes through crisp and clear, but I am unable to facilitate a steady chroma signal; the image is in black and white. I have ~.650V going into pin 4 (Chroma In) on the FMS6400, but pin 5 (Chroma Out) has no significant voltage. Are there any inconsistencies to the mod as described in the diagram, or anything I could be missing here? I also did some tweets about the state of my mod, if any of that is helpful. Cheers

[relo999]

Could someone help me?

I've got the mod kinda working on some monitors.

1 of the 3 shows no image beyond some snow (and is the oldest and not in the photo's), one shows an image but is quite desaturated and shows snow ontop and some what shakey, and one is decent beyond some hue shifting issues and minor noise but is sometimes a bit shakey (newest monitor). The shakeyness is a bit weird as the pixels don't really move but it's like "shadow" of the pixels move a bit, can be seen in the second picture with the ladders.

I've also added the 2200uf cap on the power socket but that didn't seem to do anything.

The FMS6400 also gets quite hot, I doubt that that's normal.

[relo999]

I'd edit my previous post if I could, anyway I noticed some new symptoms.

Monitor 3 has a dark purple background while monitor 2 doesn't. As seen in the pictures, but in real life it's more easily spotted. I've also tried adding a 220uf cap and 75ohm resistor to the chroma and luma out without much notable difference in output quality, however it did make the FMS6400 run cool.

Now the weird part. Monitor 2 only shows a picture if the antenna is connected to the monitor and monitor 3 has the exact opposite, it only shows a picture when the antenna isn't connected to the monitor.
Monitor 2 is my testing monitor at my soldering station and I apparently didn't ever disconnect the antenna during testing. I only disconnected it because I thought it might be the cause for the interference.

Also tried using the mod on a different cassette vision, but got the exact same symptoms.