Problem with EPROM PCB

[MaximRecoil]

The problem is that the screen is rolling. There are brief moments of stability for up to about 5 seconds, but it's rolling most of the time, like it's not syncing properly with my CRT TV. The first game I tried was a hack (Space Invaders Deluxe 8K), and I thought maybe there was some issue with the hack, so I erased the EPROM and tried an official 8K game: Defender II, and it did the same thing. So then I tried some different EPROMs. The first one I tried was a Fujitsu 27256 (I concatenated 4 copies of the ROM to make it 32K) and the next ones I tried were a National Semiconductor 27C64 and a Fujitsu 2764 (no need to concatenate the ROM file with those), and I got the exact same results. Also, I tried two different Atari 2600s: a "heavy sixer" and a 4-switch woodgrain version, both of which work perfectly with all of my cartridges, and got the same results with both.

 

The PCB is a common design that's been shared on PCBWay's website for example (link), and is sold by 8-Bit Classics (link) and maybe others. Mine came from 8-Bit Classics, and they said they would send me another one, but it might end up doing the same thing.

 

Here's a video of what it's doing (note that the title screen is stable; the picture doesn't start rolling until the attract mode starts or a game is started):

 

 

 

I also looked at the code on the GAL chip and it didn't seem to have much on it, so I reprogrammed it with the JED file from that PCBWay link, which had a lot more code in it, but I still got the exact same results.

[alex_79]

The issues you're experiencing have nothing to do with the PCB or the eproms: the culprits are the roms you're using.

Space Invaders Deluxe doesn't generate a proper VSYNC signal (it's too short, and just a few cycles longer on the title screen, which allows your CRT to sync there).

Defender II requires extra ram on cartridge, and the board you're using does not provide that.

Also, ensure to use roms with the same format (PAL/NTSC) as the console/TV you're using.

Edited August 20, 2023 by alex_79

[MaximRecoil]

8 minutes ago, alex_79 said:

The issues you're experiencing have nothing to do with the PCB or the eproms: the culprits are the roms you're using.

Space Invaders Deluxe doesn't generate a proper VSYNC signal (it's too short, and just a few cycles longer on the title screen, which allows your CRT to sync there).

Defender II requires extra ram on cartridge, and the board you're using does not provide that.

What about Activision's H.E.R.O.? I tried that one too, with the same results. Do you know of any that should definitely work?

 

If the problem with Defender II is that it doesn't have the extra RAM on the cartridge, why does it have the same rolling screen / sync problem as SI Deluxe? Shouldn't it have a completely different problem?

Edited August 20, 2023 by MaximRecoil

[alex_79]

25 minutes ago, MaximRecoil said:

What about Activision's H.E.R.O.? I tried that one too, with the same results. Do you know of any that should definitely work?

H.E.R.O has 263 scanlines, but it should work fine.

 

25 minutes ago, MaximRecoil said:

If the problem with Defender II is that it doesn't have the extra RAM on the cartridge, why does it have the same rolling screen / sync problem as SI Deluxe? Shouldn't it have a completely different problem?

I just tested in Stella by forcing the bankswitch to "F8" (without ram), and the game is unplayable but it displays a stable picture.

Check that you're using the correct rom (PAL or NTSC) and also that the code in the gal is for the right bankswitching method: F8 for a 8k game, F6 for a 16k one and f4 for a 32k one.

A 8k game will not work correctly if the gal is programnmed for a 32k one, even if you use a larger eprom and concatenate more copies of the rom.

 

EDIT:

in other words, choose the jed file based on the size of the game, not of the eprom you're using. If the eprom is larger than the game, concatenating more copies of it to fill the eprom usually works fine.

Edited August 20, 2023 by alex_79

[MaximRecoil]

45 minutes ago, alex_79 said:

H.E.R.O has 263 scanlines, but it should work fine.

 

I just tested in Stella by forcing the bankswitch to "F8" (without ram), and the game is unplayable but it displays a stable picture.

Check that you're using the correct rom (PAL or NTSC) and also that the code in the gal is for the right bankswitching method: F8 for a 8k game, F6 for a 16k one and f4 for a 32k one.

A 8k game will not work correctly if the gal is programnmed for a 32k one, even if you use a larger eprom and concatenate more copies of the rom.

 

EDIT:

in other words, choose the jed file based on the size of the game, not of the eprom you're using. If the eprom is larger than the game, concatenating more copies of it to fill the eprom usually works fine.

I've been using an 8K EPROM every time except the one time that I tried it with a 32K EPROM with concatenated ROM files, and I do know that the JED file needs to match the size of the ROM file regardless of the size of the EPROM.

 

I've attached the 2 JED files I've tried. The one named GAL20V8B.JED is the one that came on it, which I dumped before trying the other one (ATF20V8B_8K.jed) from that PCBWay share link. The code in them is very different; the one that came with the PCB has hardly any code at all.

 

I just tried Asteroids (the version with fixed VSYNC that Thomas Jentzsch posted some years ago) and it displays a stable copyright screen, but when it tries to go to the attract mode, it only shows it for a split second and resets to the copyright screen, ad infinitum. One time it stayed on the attract mode screen for a little longer, maybe 2 seconds, and you could see the screen roll. That was with the ATF20V8B_8K.jed file programmed to the GAL chip. Then I tried the GAL20V8B.JED that it came programmed with, and I just got a blank screen, nothing else.

 

Do you know if either of those JED files I attached are correct? The JED file I downloaded from the PCBWay share site is for an Atmel ATF20V8B chip, and my chip is a Lattice GAL20V8B. I'm guessing that they are interchangeable, but I don't know for sure.

jed.zip

Edited August 20, 2023 by MaximRecoil

[alex_79]

On 8/20/2023 at 3:17 PM, MaximRecoil said:

Do you know if either of those JED files I attached are correct?

The ATF20V8B_8K.jed you posted is identical to the one on this page, which is where that board design from the PCBWAY link posted above originates from.

The layout of the board shown on the 8-bit classic site looks different, so you'd have to trace it to confirm that it's the same design, and so that you can use the same code for the GAL chip.

Or just ask them for the correct GAL code.

On 8/20/2023 at 3:17 PM, MaximRecoil said:

The JED file I downloaded from the PCBWay share site is for an Atmel ATF20V8B chip, and my chip is a Lattice GAL20V8B. I'm guessing that they are interchangeable, but I don't know for sure.

They seem to be interchangeable, but I have no experience using them, so I'm not sure either.

 

[MaximRecoil]

1 hour ago, alex_79 said:

The ATF20V8B_8K.jed you posted is identical to the one on this page, which is where that board design from the PCBWAY link posted above originates from.

The layout of the board shown on the 8-bit classic site looks different, so you'd have to trace it to confirm that it's the same design, and so that you can use the same code for the GAL chip.

If you're referring to this picture on the Grand Idea Studio site, then that's a 2K/4K PCB, which does have a different layout than the 8K/16K/32K PCB that I have.

 

The ATF20V8B_8K.jed file that I downloaded from the PCBWay site shows a Rev. B 8K/16K/32K PCB, and my PCB also says Rev. B on it. I wonder if my GAL chip is defective. I don't know if it can be defective yet also program and read in my programmer without any issues.

[alex_79]

25 minutes ago, MaximRecoil said:

If you're referring to this picture on the Grand Idea Studio site, then that's a 2K/4K PCB, which does have a different layout than the 8K/16K/32K PCB that I have.

No, I looked at the gerber files for the 8k/16k/32K board on Grand Idea Studio site and the layout doesn't seem to match the PCB shown on 8-bit classic site.