Another reproduction of a custom IC successfully carried out.The part in question is the Sega ‘315-5025’, a 300mil DIP18 chip found on System 1/2 boards, Space Harrier and other Sega hardware from 80s :
It’s basically a shift register used for graphics functions being directly connected to data bus of the ROMs as per Choplifter schematics (it’s shown as a 20 pin IC because it’s compatible with the bigger ‘315-5155’ found on System 16A and Out Run boards)
Since nobody made it before I reproduced this custom my way by studying how it was reverse-engineered in bootlegs:
Testing on a Pitfall II PCB:
I hope this will help people to repair their faulty PCBs being understood that this project, like all my other, will not be made public although nowadays it’s a common thought that everything should be shared and free.Nothing in life is free and if you don’t work for it you certainly shouldn’t expect it, nor do you deserve it for free.
‘Konami-1’, a simple name given to a custom IC used on many Konami PCBs from early 80s, here’s a filtered list from MAME :
The chip itself is a 600mil DIP42 which most of times comes with scratched-off part name:
It’s basically a 6809 CPU with some minor modifications (different pinout and scrambled opcodes), it was the first custom chip ever produced by this manufacturer.
Studying how it was reverse-engineered by bootleggers I made my own reproduction of it :
Here’s testing on a Jail Break and Gyruss (bootleg) PCBs:
Probably a CPLD based version will come later in order to semplify the board layout but I’m quite happy with it as is.
A while back I got my hands on a cheap CPS1 set for Street Fighter 2 CE. The reason it was cheap was that the A board was not working. As we know by now, these A boards are dying quite fast and in some cases the culprit is the Custom CPS-A-01 chip for which there are no know replacements as of yet.
Let’s have a look at what we get on screen first
So it seems we’re only getting half the lines in the sprites and , while it’s not visible on a screenshot, the other half is flickering slowly too.
Looking at the schematics we can see the two parallel banks of rams processing each odd/even lines of sprites. These are coming straight out of the CPS-A-01 GPU IC. Let’s check out the DT/OE enable lines or the rams first.
Looking at them in with the scope reveals a couple of issues:
The bottom one is pin 21, and it’s not really toggling apart from that one regular jump, while we can see that the other line is toggling all the time. This is why we’re only seeing half of the sprites: one bank is not being enabled.
The other issue is this jump on both lines which is most likely why the entire sprites flicker regularly.
These are coming from Pin 21 and 47 of the cpsA .
bank A pin 21
bank B pin 47
Tying the enable line of bank B to bank A will restore the sprites but we still have the issue of the flickering sprites… in a nutshell, the CPS-A chip is fried and this A board is toast.
Luckily a viewer of the youtube channel (thanks Kris Ankers!) sent me a spare A & B board.
The board is in unknown working state . Checking the few remaining proms it’s another SF2 CE , not that it makes much difference here as we’re only interested in the A board. Let’s replace the A board on my other stack and fire this up
…nothing. board is dead.
A quick visual inspection reveals a few corroded badly corroded sockets on the BUF1 and ROM1 pals. corroded is an understatement here too since the socket were missing legs that had completely disintegrated.
Let’s put new sockets in place and see what we get.
Still no boot. I took both pals from my other set and dropped them in.
After some more swapping I found that the Rom1 pal is working so it was just the BUF1 pal that needed to be replaced.
Success!! The board is now booting and playable. Sound is also working fine.
But it seems we’re missing the red color.
A look at the schematics tells me me which ICs are handling the rgb output. We’ve got two rams outputting to 2 LS273 flip flops. This is then sent through ls07 and ls367 buffers, through resistor arrays before being output to rgb.
The difficulty here is that apart from the legs of the rams and resistor arrays which can be probed from the underside, the other ICs are SMD and hidden by the b board so I am not able to probe the legs. Time for some logical guess work :
Since the pairs of ls07 and ls367 are shared across the colors it’s unlikely one of those has failed or it would affect more than one color (still possible but unlikely)
Two resistor arrays are needed per color. If one had failed, we’d get some red at least but here it’s all gone and while it’s possible, it’s unlikely two are gone
So I’m first going to look at the RAM at 1C and the 273 at 4C
Probing the RAM seemed ok so I decided to remove 4C and replace it.
Bingo!
Behold a working (for now) Street Fighter 2 CE CPS1 stack. It’s a bittersweet victory though as there’s no telling when that CPSA chip will fail (not if but when) . But for now I’m going to enjoy some Capcom fighting. Thanks Kris for the PCB donation !
A friend of mine sent me a couple of Vanguard pcbs which didn’t sync at all on all monitors I tested.
The only difference I saw was that his pcbs were Centuri versions while my pcb which synced good was SNK version.
Centuri versions on the video board have a factory mod with some flying wires which are not documented on the schematics and which are related to the sync circuit.
SNK version has no flying wires on the video board:
offcourse undoing the factory mod on the century board fixes the sync problem but I wanted to learn something more.
It seems that Centuri versions were modified to use the positive sync monitor supplied in their cabinets and probably they also improved the sync
signal in comparison to the original circuit.
Anyway , if you want to keep the mod but invert the sync for common monitors or TVs, you have only to solder the wire which goes to pin 3 of the 74LS05 marked in red
While cleaning the storage I found a very interesting power supply made by Sanwa and marked SNW-7E which works with 110 or 220V
The model SNW-7F is the same model working with only 110V
It’s a very nice and compact power supply ( with a tendency of getting really hot!) and I learned that it was used on the most famous japanese superguns .
When I powered it up it worked but on the -5V line I got -7,5V .
I decided to try to repair it and fortunately the -5V was given by a 7905 regulator with few parts around.
I immediately noticed that the regulator didn’t regulate at all since it passed exactly the same voltage on the input on its output.
Replacing it with a new 7905 fixed completely the problem
Note:
it turns out that this power supply is just a rebadged version of the RT-85A model made by Taiwanese company Meanwell
