Muddymusic sent me a Dangerous Curves PCB which has a load of unlocked PALCE16V8 devices on it.
I dumped them all using my programmer.
The PCB is a non worker so I cannot test these but they are assumed working at this point.
Thanks to my good friend Muddymusic for this
From time to time we get a message saying a PAL we have doesn’t work. Usually when this happens there is little we can do as we no longer or never did own the PCB. On this occasion however we found a resolution.
Kyle point out that the file we had for Super Pacman 1M didn’t work for him. He claimed the equations for the PAL didn’t include the use of input pins 5 and 6. To back up his words with a schematic showing then attached.
The strange thing about this is he also dumped the PAL in his programmer and got the same output file as the original dumper (Channelmaniac) did.
From here Kyle built the 27C020 adapter and bruteforced his PAL chip. This time he got something that did work.
His recreation is now available for download in place of the old one.
I have a suspicion the Topmax programmer has a little bug in the handling of PAL10L8 chips although the other dump supplied by Channelmaniac supplied does work without issues so who knows.
Quick repair this one.
Received this board recently from a great eBay seller.
It was sold as faulty and indeed it was. On power up I was greeted with this static screen.
As the Z80 is already socketed on these boards I hooked the Fluke 9010 straight up and did a RAM test. As I was expecting, this failed.
The main RAM is located next to the 4 program ROM’s. One socket and one new RAM chip and we have a nice easy fix.
The second of Alex’s board for repair is Donkey Kong Junior.
This board booted to static screen that wouldn’t sync. This ended up being a broken 30k pot on the H-Sync.
As I don’t currently have and 30k or 50k pots I opted to temporarily fit an 18k resistor to the video PCB to let me move on.
The game now booted to a static screen of garbage but when touching the Z80 CPU it booted. The socket looked old and a bit crusty so I replaced it.
The game now played but there was a lot of garbage still on the screen.
I hooked up the Fluke 9010 and did some basic reads and writes to the video RAM that sits between address 0x7400 – 0x77ff.
Clearly bits 0 and 1 were stuck low.
Using the schematics I started checking at a 74LS245 at location 6A which buffers the databus.
Straight away I found although the signals were going to the chip the outputs on DAT0 and DAT1 were floating.
As the outputs were floating I tested by piggybacking a good 245 chip and everything came up good.
Replace the 245 and fitted a new one.
Tested the game and all sound and controls work too.
Another one fixed.
Got a Donkey Kong 3 to repair from my good friend Alex @ Nintendo Arcade
On boot up I got a static green of garbage
I checked the voltages at the far end of the PCB and saw they were quite low compared to what my PSU was set at. Adjusting the voltage to a bit higher brought the PCB voltage back up to a good point but made no difference to the fault.
Next job was to check the program ROM’s
Found 7C, 7D & 7E had suffered from bit rot. I erased these and reprogrammed them with the correct data from the MAME set.
It didn’t make any difference at all so I started looking at the Z80 CPU signals and this is where I got a little confused.
At first glance and without really engaging brain too much I automatically assumed that there were two Z80 CPU’s side by side but checking the voltages and the signals left me scratching my head as they were not what I had thought. On closer inspection I realised that the one on the left is actually a Z80 DMA chip. I’ve not seen or even heard of these before so it something new to me.
I took to the internet and downloaded the datasheet for the DMA chip and also the schematics for this PCB too.
The CPU and the DMA chip are tied to the same busses and the DMA chip didn’t appear to be releasing the data bus to allow the CPU to do its thing.
I checked all the incoming signals to the DMA chip but found nothing odd so at this point I figured I needed to buy a new DMA chip so ordered one from eBay.
To help confirm my diagnosis I pulled the DMA chip and powered up the game. Sure enough it booted fine and ran but was missing the sprites which is to be expected really.
A couple of days later I received the new chip and now we get this
All sound and controls working too so that’s this one sorted.
There appears to be some skewing at points in the pictures above. This is due to my supergun setup and not a PCB fault.