Hello everyone, today I have another board on my desk which I purchased as “working” but while my board boots up, it has issues.
Irem produced several models of motherboards, and this motherboard is M92. It is a 2-stack board, consisting of a motherboard and a ROM board. M92 does not have any schematics.
BUT wickerwacka produced some partial schematics of the M92 when implementing his FPGA core. Also take a look at that valuable source Irem M92 entry in PCB Encyclopedia]
First let’s take a look at our board.
Main board:
ROM Board
When I power up the board, it passes the RAM and ROM test successfully.
However, in the warning text, you will see a line at the bottom of the screen. That’s one of our problems.
Here you can see another problem, there is a vertical line on the left and right of the screen.
These are the most obvious problems. It is difficult to show the real problem with a photo.
Take a look at this video of the problem:
As you can see, as our character moves forward and the background changes, there are flashes and/or color changes on the screen. This is our biggest problem.
Let’s do a physical inspection. The ROM board seems clean and problem-free enough. I move on to the motherboard.
The mainboard has been worked on before – one of the chips has been changed or reflowed.
When I look closer, I see a solder bridge. This bridge belongs to 74LS74AN part.
I separate the bridge with a tiny touch of a soldering iron.
But removing this bridge causes no change with the game.
Next, I keep the game on for about half an hour, then I check the chips one by one to see if any of them are overheating. It seems that three of the ICs on the ROM board, which I have highlighted in blue, are overheating.
One by one, I remove the parts and test them out of circuit with my EPROM programmer. One of the SN74S373N parts fails the test.
I install socket and replace all three parts.
IC18
IC30 and IC31
Unfortunately, there’s no change in the game – but there’s no more overheating chips now either.
The next task is to check the ROMs by dumping them and comparing the dumps with MAME. I remove everything from the ROM board (both for cleaning and to check the ROMs)
I set the chips down on a notebook in the same order so I don’t forget their places.
When dumping the ROMs, if it is not written on the chip you are reading what type of part it is, we either check MAME or we look for solutions in forums.
Also, part numbers for ROMs with Irem M92 boards are here
There were 3 types of ROMs on this board. Let me specify how to read them:
532 –> 27C020
534 –> 27C040
538 –> 27C080
After dumping the ROMs and comparing them, it seems that most of them are okay.
L0
L1
Irem produced several models of motherboards, and this motherboard is M92. It is a 2-stack board, consisting of a motherboard and a ROM board. M92 does not have any schematics.
BUT wickerwacka produced some partial schematics of the M92 when implementing his FPGA core. Also take a look at that valuable source Irem M92 entry in PCB Encyclopedia]
First let’s take a look at our board.
Main board:
ROM Board
When I power up the board, it passes the RAM and ROM test successfully.
However, in the warning text, you will see a line at the bottom of the screen. That’s one of our problems.
Here you can see another problem, there is a vertical line on the left and right of the screen.
These are the most obvious problems. It is difficult to show the real problem with a photo.
Take a look at this video of the problem:
As you can see, as our character moves forward and the background changes, there are flashes and/or color changes on the screen. This is our biggest problem.
Let’s do a physical inspection. The ROM board seems clean and problem-free enough. I move on to the motherboard.
The mainboard has been worked on before – one of the chips has been changed or reflowed.
When I look closer, I see a solder bridge. This bridge belongs to 74LS74AN part.
I separate the bridge with a tiny touch of a soldering iron.
But removing this bridge causes no change with the game.
Next, I keep the game on for about half an hour, then I check the chips one by one to see if any of them are overheating. It seems that three of the ICs on the ROM board, which I have highlighted in blue, are overheating.
One by one, I remove the parts and test them out of circuit with my EPROM programmer. One of the SN74S373N parts fails the test.
I install socket and replace all three parts.
IC18
IC30 and IC31
Unfortunately, there’s no change in the game – but there’s no more overheating chips now either.
The next task is to check the ROMs by dumping them and comparing the dumps with MAME. I remove everything from the ROM board (both for cleaning and to check the ROMs)
I set the chips down on a notebook in the same order so I don’t forget their places.
When dumping the ROMs, if it is not written on the chip you are reading what type of part it is, we either check MAME or we look for solutions in forums.
Also, part numbers for ROMs with Irem M92 boards are here
There were 3 types of ROMs on this board. Let me specify how to read them:
532 –> 27C020
534 –> 27C040
538 –> 27C080
After dumping the ROMs and comparing them, it seems that most of them are okay.
L0
L1
