My R-Type developed a fault years ago; what started as a line of garbled data in the center of the screen deteriorated into the loss of all sprites and corrupt data on the screen.
It sat for years on the shelf as I lacked the skills to repair it, but gradually came to suspect the custom Nanao at 2S (IC10). I was gutted but consoled myself by converting a major title to a 'par-type' hack that I did have ths skills to do.
Trying again I confirmed my earlier suspicions; the address lines to the sprite roms were garbage, fluctuating in a square wave but only with a range of 0.2v. This all traced back to the custom Nanao, labelled KNA71H009(13).
I knew that M72 and M82 were almost identical hardware, and had a dead major title PCB with a good bottom board. It occured to me that the customs on the Major Title had a high probability of being identical to those on the R-Type. However on the Major Title the chips all had their ID scrubbed off.
So I looked at the mame driver to find where the sprite roms were on major title, and looked at the rtype schematic to find where the adress lines went to. I then traced the equivalent address lines on the major title to identify the custom that handled sprite addressing. As it happens there are two on a major title as M82 hardware has an extra bank of sprite roms. These are located at IC42 6J and IC43 at 6L. The address lines matched those on an rtype so I decided they were very probably the same chip.
So all I had to do was desolder a 64 pin custom with a non-standard pitch. This was a complete pain in the arse but eventiually withe at least two passed with the desodering pump I coaxed it free. I decided to piggyback the chip as it fit quite snugly over the dead one and figured the weak outputs of the existing custom wouldnt interfere.
With some trepidation I plugged it in and hit the power switch.
BINGO
R-Sprites!
Now all I had to do was remove the dead custom. I decided to dremel this off as my snips are a bit crap and with it being a 64 pin chip with a narrow pitch that would be a struggle. As PCBs dont tent to enjoy being covered in metallic swarf I masked off the rest of the PCB, cut off the chip, then methodically cleared the pins and solder of the dead custom.
I have no sockets for this chip so just soldered the chip from the Major Title straght in, then put it back together and plugged in.
Really happy I've one of my favorites back up and running.
Slightly guilty for giving last rites to what was already a faulty major title, but I'ts worth it in this case.
grobda2016-03-05 13:02:53
It sat for years on the shelf as I lacked the skills to repair it, but gradually came to suspect the custom Nanao at 2S (IC10). I was gutted but consoled myself by converting a major title to a 'par-type' hack that I did have ths skills to do.
Trying again I confirmed my earlier suspicions; the address lines to the sprite roms were garbage, fluctuating in a square wave but only with a range of 0.2v. This all traced back to the custom Nanao, labelled KNA71H009(13).
I knew that M72 and M82 were almost identical hardware, and had a dead major title PCB with a good bottom board. It occured to me that the customs on the Major Title had a high probability of being identical to those on the R-Type. However on the Major Title the chips all had their ID scrubbed off.
So I looked at the mame driver to find where the sprite roms were on major title, and looked at the rtype schematic to find where the adress lines went to. I then traced the equivalent address lines on the major title to identify the custom that handled sprite addressing. As it happens there are two on a major title as M82 hardware has an extra bank of sprite roms. These are located at IC42 6J and IC43 at 6L. The address lines matched those on an rtype so I decided they were very probably the same chip.
So all I had to do was desolder a 64 pin custom with a non-standard pitch. This was a complete pain in the arse but eventiually withe at least two passed with the desodering pump I coaxed it free. I decided to piggyback the chip as it fit quite snugly over the dead one and figured the weak outputs of the existing custom wouldnt interfere.
With some trepidation I plugged it in and hit the power switch.
BINGO
Now all I had to do was remove the dead custom. I decided to dremel this off as my snips are a bit crap and with it being a 64 pin chip with a narrow pitch that would be a struggle. As PCBs dont tent to enjoy being covered in metallic swarf I masked off the rest of the PCB, cut off the chip, then methodically cleared the pins and solder of the dead custom.
I have no sockets for this chip so just soldered the chip from the Major Title straght in, then put it back together and plugged in.
Really happy I've one of my favorites back up and running.
grobda2016-03-05 13:02:53
