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Got F18A installed some games don't work/black screen


Mika73

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Correct, I mentioned in my post #9 update that I am using the same power brick (a U.S. 60Hz) for both the PAL and NTSC motherboards. It is the only power brick I have.

 

I observe the problem with games that do not enable the VDP interrupt until after the difficulty screen. Donkey Kong is one such game. However, games like DK Junior work on both machines all the time and the interrupt is active from the title screen. On the PAL CV I have, the problem also degrades after the unit has been on and reset several times, which is why I think it may be a failing component of some sort. But I'm still not sure or convinced.

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  • 3 weeks later...

Quick update. It seems the problem with the PAL consoles is related to the F18A driving the CPU's interrupt. I had problems with this initially while developing the F18A and the solution was a 100-ohm resistor between the FPGA and the interrupt output pin. To prove or disprove this possibility, I modified my test F18A and removed the resistor (soldered a small jumper across the PCB pads where the resistor goes) and it seems to have fixed the problem. Donkey Kong, which was failing before, works 100% now over ten or so tests (power-off, power-on, reset, re-insert the cartridge, etc.) Just because I like having a resistor in there, I doubled two 100-ohm resistors on the PCB pads to make the equivalent of a 50-ohm resistor, and it also works just as reliably as the jumper.

 

I need to do more tests, but my multi-cart is acting up and I don't have any other carts to test with. Is anyone else with a PAL CV (and having this problem) willing to make the mod to their F18A to test? Not having the resistor in the circuit will not hurt anything, but you will need a decent soldering iron and such.

 

The resistor in question is R18 and is pretty accessible on the board. A jumper across the pads, or a resistor between 1-ohm and 50-ohms should all work equally well.

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post-24952-0-39774200-1489683500_thumb.jpg

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This is not really a fix, just a test. I originally added the 100-ohm resistor because without it the F18A could not drive the Z80's NMI input. Now it seems ironic that removing it seems to help the problem with the PAL CV. However, I still do not know why, and this modification is not 100%.

 

I do have another test that I am running where I am driving a standard TTL 74LS logic gate (an OR gate in this case) from the FPGA, then driving the interrupt output from the OR gate. It looks like this:

 

FPGA ---> 74LS32 ---> Interrupt output.

 

This configuration works, and on the PAL CV I am testing with I have been able to run every game listed as not working, including River Raid, Gyruss, Donkey Kong, etc. There are three problems with this fix:

 

1. Using 74LS logic is too big for the F18A (I'm looking for an SMD alternative that uses real TTL logic).

 

2. It would require a significant modification to existing F18A boards (although only those having problems would need to apply the fix).

 

3. I still do not understand why the existing F18A circuit does not work, so my fix is still just a hack and that bothers me.

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Quick update. It seems the problem with the PAL consoles is related to the F18A driving the CPU's interrupt. I had problems with this initially while developing the F18A and the solution was a 100-ohm resistor between the FPGA and the interrupt output pin. To prove or disprove this possibility, I modified my test F18A and removed the resistor (soldered a small jumper across the PCB pads where the resistor goes) and it seems to have fixed the problem. Donkey Kong, which was failing before, works 100% now over ten or so tests (power-off, power-on, reset, re-insert the cartridge, etc.) Just because I like having a resistor in there, I doubled two 100-ohm resistors on the PCB pads to make the equivalent of a 50-ohm resistor, and it also works just as reliably as the jumper.

 

I need to do more tests, but my multi-cart is acting up and I don't have any other carts to test with. Is anyone else with a PAL CV (and having this problem) willing to make the mod to their F18A to test? Not having the resistor in the circuit will not hurt anything, but you will need a decent soldering iron and such.

 

The resistor in question is R18 and is pretty accessible on the board. A jumper across the pads, or a resistor between 1-ohm and 50-ohms should all work equally well.

i dont mind giving this a go on mine with a jumper (wire) if that will help?

actually you probably don't even need to remove the resistor, just solder a wire on to each side, essentially turning it into a 0 ohm resistor as the easiest route will always be take which will be the wire. this would save removing the component

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I'm still working on it. I cannot get any consistency in my testing when I make changes or try different components. Very frustrating. I'm very certain the problem is the interrupt, but I cannot determine exactly how or why.

I remember the Z80 is prone to errors if NMI isn't steady for some number of cycles. I would suggest pull up resistor to 5V+ and a decoupling capacitor to ground to trap "spikes".

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  • 2 weeks later...

@nanochess: The main problem with adding components to the interrupt line is that I have no idea what computer the F18A is going into, and I can't possibly survey and accommodate every possible hardware situation. I have to be electrically compatible with the original VDP, which in the case of the CV the interrupt line goes directly to the Z80's NMI via a single trace (as well as the expansion port pin). I'm pretty sure the problem is not noise on the line, my o-scope tests show really clean interrupt signals.

 

Update: Do NOT modify your F18A as mentioned above as a possibility. Some recent tests are pointing in a different direction. I'll know more soon.

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  • 2 weeks later...

I'm jumping in here since I seem to have thesame issue, although I don't own that many games to test with. I also have a PAL unit with donkey kong not booting after the player choice, while other games (Smurph for example) work fantastic. Really blown away by the image quality btw Matthew. Running it through an internal vga-hdmi convertor on a large samsung lcd. Following this with interest.

Edited by Unstablewarpfield
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I don't think there will be a solution Mika, considering the last thing we heared is from over a year ago. I guess that's life though.

Then again, I can't seem to find our problem under the "known quirks" section on matthews website which potentially could mean that people with a PAL system will be buying the F18A while being unaware of this issue, which is not very nice in my eyes since it is not a cheap mod. Add to that also import fees and taxes and you are looking at a 100 euro upgrade that probably does not work with some games.

 

I am now hoping that the PAL version of citrus3000psi mod will work. Time will tell...

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my solution to the problem was to get a non working US colecovision and fix it, then install the f18a in that

 

to be fair all my coleco's have been non working in some degree and i have 3

 

im sure its still being worked on, matthew unfortunately does sometimes take quite a while to reply

 

there is that rgb mod board in another thread that may work, but the pal version is self assembly using surface mount components so is not for the feint hearted unfortunately

i have got the first batch of components for the ones i have, depending on how that goes is whether i contiiue and get the otehr needed components or not

 

https://oshpark.com/shared_projects/ogorMaoU

Edited by omf
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