Colecovision Speed Control Dial Mod? (Is it possible?)

[parkfun101]

I'm a bit new to the electronics bit, but I have made my own AV mods, Power indicator leds, done the Rocker Power switch mod (definitely recommended) and have done the Pause mod on Colecovisions, but I was wondering about a mod that I haven't heard about. Is it possible to make a Colecovision have a speed dial or to make it a bit faster and/or slower (perhaps with a potentiometer)? The reason I like this idea as a mod is the same reason I don't play Street Fighter II anymore, instead I play Street Fighter II Turbo. I like the faster speed. However, in some games for Colecovision like Montezuma's Revenge, I think the game moves a bit too fast and would like to slow it down. Think of going back through your entire Colecovision collection and replaying all of your games at a slightly faster or slower speed. This would perhaps increase or decrease the difficulty and would be a pretty AWESOME mod since it would affect the actual gameplay.

I have 4 Colecovisions to test this out on, but I need the community's help to do some tests. I'm not up on all the jargon, but if you say that part at U22, replace it with bla bla bla. I understand that. I know people are a bit reluctant to fool around with changes like this on their own system, that's what I'm here for. You give me an idea of what parts to change/modify or whatever, and I'll fool around with my extra Colecos and perhaps we, as a community, can create one of the coolest mods EVER for a Colecovision. On top of that, I'll make up FULL documentation on what changes would be needed and re-post on this site so anyone (with a soldering iron) could do it. I may even post a YouTube video as well.

So, if you have any ideas, please feel free to post them below.

[fiddlepaddle]

This is only theory, but it is probably possible to change the speed by changing the frequency the CPU/memory operates at. I know, at least with other computers of the era, you could swap in a new crystal and change the speed of your computer. Might be difficult though, if the video out circuits are tied to the rest, as that would mean the video would no longer be compatible with the TV.

 

Speeding it up too much could stress components that weren't made for that, and slowing it down too much might let things like memory chips lose their memory.

 

Interesting question...looking forward to hearing from some people who actually know what they're talking about...

[+5-11under]

Here's what I would do:

 

1. Install an F18A. I think (I'd check first) that this can run at faster bus speeds than the standard VDP. The standard VDP is expecting a certain clock frequency, and if you deviate from that, I'm guessing you'd be in trouble as far as video output goes.

2. Install a faster Z80 processor. I'm assuming the BIOS and RAM can handle faster speeds, but otherwise upgrade those, too (check as per the part numbers, in the least).

3. Change the crystal from 7.15909 MHz to a faster one (the Z80 runs at 0.5 times that frequency, and the VDP runs at 1.5 times that).

4. Build a circuit to modulate the pulse widtch of the halt signal on the Z80. Basically pause and un-pause the processor at some medium speed. This seems to work fine with a wire or switch, and hopefully it would work okay on a regular basis.

[parkfun101]

Hi 5-11under,
Remember, I'm fairly new to electronics...been doing this for about 3 months now. So bare with me on the questions/statements below.

1. Install a F18A (not sure what that is or where I would install it on the board). Faster bus speeds than the standard VDP.....I'm not sure what a VDP is or where it is located on the board.

2. So change the Z80 processor to something faster, upgrade BIOS and RAM if needed. What processor would be recommended? I don't mind buying several different kinds until I get it working, but I haven't a clue about which one would be applicable.

3. Change the 7.15909 MHz crystal that is near C70 to something faster. I'm looking at the following site for crystals and crystal oscillators. It allows you to search by frequency. Which ones should I try out?
http://crystal-oscillator.tedss.com/

4. Need a switch or wire from the Halt Signal on Z80 to.... ground maybe....is that where I would connect it to? I'm thinking of how the Wait signal works for doing a Pause mod.

[+5-11under]

1. Search for F18A ColecoVision for the answers to what the F18A is. It's a VDP in an FPGA. The VDP (video display processor) is normally a TMS9928A (for NTSC). In the CV it has a heatsink on it.

2. A faster Z80. Currently runs at 3.58... MHz. Usually 4 MHz is the maximum. You can get them in 6, 8, 10, or 20 MHz versions. If available, just get a 10 MHz version. It's a maximum, so can be run slower.

3. Just make sure it has only 2 pins (if it has 4+ pins it's probably an oscillator). Search for crystal mhz and you'll find ones that look like the one on the CV PCB. How fast do you want to go? 8 MHz? 9 MHz? 10? The higher you go, the more likely you'll run into other problems that the designers of the PCB, etc., didn't accommodate or test for.

4. Yes, you're right. The Wait signal: http://atariage.com/forums/topic/149407-colecovision-atari-module-switch/?hl=%20add#8208a. Connect and disconnect to ground with a wire to simulate how the circuit would work... then find a clock circuit that will allow you to change the duty cycle of the signal.

[parkfun101]

I get it, so right off the bat, I could probably go ahead and do a test. I could make that clock circuit and hook it up to the wait signal so it will basically pause and unpause at a certain rate giving me a slower speed game. Later, I can change the hardware to basically go faster and then hook it up to my clock circuit wait signal thing and it should allow it to go from Faster to slower speed games, in theory. That is an excellent idea!!!

I'm going to work on the clock circuit portion first since that requires no real need for new hardware besides some wires and the clock circuit items. I'll let you guys know if I can get that portion working.

[NIAD]

F18A VGA Video Upgrade Board:

 

http://codehackcreate.com/

[ValkerieSilk]

Always loved Ms. Pacman on hi-speed... Great idea for CV...

[parkfun101]

I did get a circuit put together that makes an led blink on and off somewhat fast. I must not have connected it correctly to the Colecovision to the wait and ground because it would either just pause for a half second or so and then resume with no more pausing or it wouldn't do anything but play like normal.

Also, I did a basic test with the Colecovision wait and ground. I basically just touched the wires together for wait and ground over and over repeatedly to see if the Colecovision could handle it. For the first few seconds, it appeared it would pause, resume, pause, etc just fine. After a few seconds the system would either restart or the game crashed, graphics would look all jumbled and the sound appeared stuck.....one of those "That didn't work" moments. I'm not sure if this is because of me manually touching the wires together or if it is a sign that this idea just won't work....I'm not sure. I guess if someone has a pause mod on their system, they could just try turning it off and on rapidly for like 10 seconds or so to see if something goes wrong. For me a simple reset worked fine and I didn't notice any issues with the Coleco after that.

Another idea with this, bear with me now - I'm not sure if this is possible or not, is to have a 3 way switch. Position 1 would connect a slower crystal to the Colecovision, Pos 2 would be the normal crystal and Pos 3 would be a faster crystal. Again, this is just a thought, and I have not tested crystals yet to see how they change the speed of the Colecovision.

[NIAD]

Would it be possible to use an emulator such as BlueMSX to see what the effects of changing the emulation speed will have on games? For instance, BlueMSX allows one to change the emulation speed from 3.579MHz (100%) all the way down to 0.357 (10%) or 35.795 (1000%) and I seem to recall M.E.S.S. having a similar option.

 

I'm guessing not as real hardware probably would react differently, but it's worth a look instead of performing all the physical mods to see what happens.

[parkfun101]

Yeah, sure, try it out and let me know. Perhaps we can at least get an idea of what maximum and minimum values work the best for most games.

 

I just got a "not working" Colecovision today. I put it in quotes because I got it working with the simple power switch mod...it's not perfect, but not bad for $25. This will be my test machine for swapping out crystals, cpus and whatnot.

[+nanochess]

You can slow down the Z80 processor just messing with the WAIT signal, but it must be "modulated" with a 74LS74 so it's synchronized to the clock, otherwise it fails.

 

Besides if I remember right, the Colecovision already generates WAIT signal, so you would have to make some kind of "adaptation" logic.

 

Most games expect to do some work when video processor generates the frame interrupt, so there is a >big< chance that the game will fail if another video interrupt comes because the Z80 is going very slow.

[parkfun101]

I did some easy tests using blueMSX. If you open blueMSX and go to Options > Emulation, an Emulation Speed control is shown in MHz. The default is 100% 3.579Mhz which is the current CPU speed of the Colecovision. You can change this value with the slider and then play the game again at the new speed. I tested these Emulation speeds out:

83% 2.977MHz(didn't have 80 as an option) ---> Good Slow speed, Montezuma's Revenge was easier to play, almost seemed like this was the intended speed for it.
120% 4.303MHz ---> Good Fast speed, I tried Donkey Kong and Mr.Do! and both games played fairly well and it was fun....not too fast.
125% 4.506MHz
151% 5.417MHz

I felt that 120% was a good "fast" speed that is not too fast. So basically, if we can speed up the Colecovision game play by 20% that would be great for the fast portion. I know that the Crystal used in the Colecovision is at 7.15909 MHz. If I wanted it to be about 20% faster, it would need to be about 10.2505 MHz. I could run by Radio Shack and see if they have a crystal like that and plop it into my test machine just to see what happens. Now, of course, that doesn't mean it will work, I know some other components may need to be swapped out as well, but I figure I can test it out first and see how it goes. Perhaps the other components may be able to handle the speed increase....not sure.

[mightywiz]

I'm going to chime in on this, i'm looking for a schematic for the colecovision. I need to see the circuitry associated with the crystal section.

depending on how it's built it may be as easy as adding a trim pot for capacitance, resistance, or inductance.

 

if you have a schematic can you post here and i'll look at it.

 

I'm a component lever repair tech schooled back in the 80's when we actually fixed electronics, so I do have some skills i'm willing to share.

[parkfun101]

Here are the schematics:
http://console5.com/wiki/Colecovision#Schematics

Any help would be truly appreciated! I'm hoping to find a solution that is somewhat affordable and available to the public as a mod.

Added some images below
Here is the board:
http://atariage.com/forums/gallery/image/10495-colecovision-board-h2-1/

Here is the crystal:
http://atariage.com/forums/gallery/image/10496-colecovision-board-h2-1-crystal/

Edited April 24, 2014 by parkfun101

[adamcon]

I'm going to chime in on this, i'm looking for a schematic for the colecovision. I need to see the circuitry associated with the crystal section.

depending on how it's built it may be as easy as adding a trim pot for capacitance, resistance, or inductance.

 

if you have a schematic can you post here and i'll look at it.

 

I'm a component lever repair tech schooled back in the 80's when we actually fixed electronics, so I do have some skills i'm willing to share.

 

If you need some evening reading, get the ColecoVision Technical Manual here: http://ann.hollowdreams.com/programming.html

[+5-11under]

Do you have an F18A, though?

[parkfun101]

No, at this point, I haven't gotten any parts yet.

[parkfun101]

For whomever is interested. Here is the schematic for the clock. It looks like there is a place at the bottom left of this image for a resistor that is not installed.....It actually says "Not Installed". I'm wondering what happens if you put a resistor or pot there??? I could test it and find out, I'm just not certain what type I would need for the test.

http://atariage.com/forums/gallery/image/10497-colecovision-clock-schematic/

[+5-11under]

Resistor in parallel with crystal:

 

Best case: CV still works.

Worst case: CV doesn't work.

Not really any in-between cases for this... it just adds a load, which usually isn't needed. Definitely no speed difference here.

[parkfun101]

Thanks for saving me time and effort 5-11under. I'm going to start looking for crystals. ...I think I like the idea of just a Normal and Fast speed Colecovision that could be controlled by a simple switch. If I can get that far, a dial could be another alternative, but for now, just getting a faster speed would be adequate....and awesome.

If it doesn't work by simply replacing the crystals and perhaps the CPU or some cheaper items like that, I'm not all that interested in pursuing this much further at this point. The F18A seems a bit pricey from what I'm seeing and my goal is to find a somewhat cheap way to speed up the Colecovision....that and I have to wait till I get my rental home rented out. Once that is rented out, I can probably pursue the F18A as well (if needed).

[+5-11under]

There's a reason the F18A was the first item in my list. The standard VDP requires about 10.7 MHz (7.15909 * 1.5) clock input to output a proper 3.58... MHz video signal. The ColecoVision divides the 7... MHz crystal by 2 for the Z80, etc., and then triples that for the standard VDP. The F18A (from what I understand!! - I have not verified this with the creator) has its own clock source and should be able to handle a variety of address/data bus frequencies. The F18A also creates its own output timing (once again, contact the creator for the real answer). The standard VDP input clock and video output and address/data bus timing are all linked together, so if you increase the input clock, then the output gets affected also. If you change the crystal from 7... MHz to 8 MHz, the video output will no longer be NTSC compliant.

 

Sorry, I'm rambling. Anyway, who knows, maybe it will work if you just change the crystal. Advice: change it as little as possible, especially in the initial testing phase. Try it out on a number of TVs to see if any are able to handle the signal. Perhaps one (or more) may be able to. Change the crystal further away from normal, and see what happens. Perhaps "digital" TVs or certain converters will be okay with the odd timing.

[parkfun101]

I'm going to try and make it so it is easy for me to swap out different MHz crystals quickly and I'll do what you said by starting small and working my way up to see what happens. Since it seems that crystals don't cost all that much, I figure I could try that first by itself. If each crystal fails to work, then I'll go to the next step of looking into the F18A. However, if the crystals work and we don't have to change anything else, we could avoid having to buy too many components and that would be great. Unfortunately, Radio Shack didn't have any crystals, I even checked a computer store near them. I'll check online when I get home and I'll see what I can find.

[parkfun101]

Ok, a Friday update on the quest for a speed boost switch (Normal to High speed):

1) I've ordered some inexpensive parts!

 

Crystals I have purchased from Mouser Electronics that have the 2 wires coming out and look identical to the ones in the Colecovision (for less than $2.00 + shipping):
7.3728 MHz
7.6 MHz
8.0 MHz
8.192 MHz

CPU Processor: ($4.00 + $4.00 shipping):
Z80 10MHz
When testing on BlueMSX it messes up a bit on Donkey Kong on 2nd and 3rd level 6MHz works fine. If I need this I will go back and get the 6MHz, but for testing it should be fine. I'll only put this in if I have problems with the crystal tests.

2) I've breadboarded the Crystal out of the Colecovision! I desoldered it carefully and gave it longer leads so it could fit in a breadboard. I then connected two 12" long wires from where the crystal used to be to the breadboard and fired up the Colecovision. It played about the same as before with a bit more static, but this is not a perfect Colecovision. I played through the 1st level on Mr.Do! using the breadboarded crystal. So when the other crystals come in, I should be able to easily swap them out and try again. Even though this is not a perfect working Colecovision, since the test is about the speed, that is all I care about, I know some static is occurring with this machine and it should not affect the tests.

[Kiwi]

I think at a higher processor speed, you're bottlenecked by the VDP speed. So any graphic heavy stuff like scrolling, mass tile update might either get corrupted or the CPU waits til the graphic finishes update. I think increasing the VDP speed will help, and I think it will increase the sound pitch as well.

BlueMSX has a speed dial at the lower right corner. That only change the emulation speed. You can change the z80 processor speed by going to machine editor>extra. Last time I experiment with that result BlueMSX not working for some reason.