30 Nov 2016

Fire Shark (Same! Same! Same!) - Toaplan 1990 (repair log)

The board is in very good condition. However after powering it, it's stuck on a work RAM error:



To me the work RAM should be the one connected directly to the main CPU (68k). As the 68k is a 16 bit processor the work RAM is actually 2 RAMs type 6264 (one for the LSB, one for the MSB). So I pulled both (@ J10 and L10) and put 2 fresh ones instead. No results. As I was unsure I replaced the work RAMs I contacted Caius from jammarcade who confirmed the work RAMs are the ones connected to the main CPU. I put the board aside and few weeks later it didn't boot at all. I had to reflow the big SMD custom chip @ J18. Back to the work RAM error...
After some more weeks I decided to check traces around the work RAMs and found 2 bad. I patched them and the game booted:





Game fixed.

23 Nov 2016

Snow Bros - Toaplan 1990 (repair log)

The game starts, controls and sound work but graphics are severely corrupted:


A lot of Toaplan games from that era use DRAM for graphics. And they are the weak point most of the time. This board was no exception. All 4 DRAM are bad (@ IC23, IC24, IC25, IC26). Once replaced everything was back to normal:



Game fixed.

16 Nov 2016

Exerion - Jaleco 1983 (repair log)

This game has a specific 36 pin connector so I had to build a converter (to JAMMA).
First symptoms were no video signals (no sync) but sound worked: replaced 74LS74 @ M9.
Then black screen with sound: replaced 2 * 153s @ D2 & E2.
I obtained an image but with a corrupted sprite layer (completely covering the background layer):











I replaced 2 RAMs @ B11 & D10:








I finally noticed dipswitches 1 were not working: replaced 74LS245 @ M2.

Game fixed.

9 Nov 2016

Sega Game Gear country switch

Despite the fact the Game Gear isn't region zoned, it does exist a difference between a Japanese model and an overseas model (USA/EUR).
Just like the Master System and the Megadrive, a specific pin on one of the ASICs specifies the region.
This has the following impact: some Game Gear games display  different title screen or Japanese texts when played on a Japanese Game Gear. Same goes with Master System games played with a Master Gear converter.


Material needed:
- a cruciform screwdriver
- a gamebit screwdriver (for the cartridge port screw)
- a soldering iron and some solder
- thin wire (kynar for instance)
- a small needle
- an ON/ON switch (SPDT type)


Step 1:


Open the console : there are 6 cruciform screws and 1 gamebit screw



The two halves can be separated by removing the 3 cables linking them together:


Step 2:

Identify the concerned chip:

For a model 1:


For a model 2:


Step 3:

Identify the concerned pin:

For a model 1 (7th pin in the left row starting from the bottom):


For a model 2 (3rd pin in the top row starting from the left):



Step 4:

This is the tricky part. Heat up the pin with your soldering iron and lift it with a small needle.
Be careful not to bridge pins together, lift other pins or break any pin.

Step 5:

Install the switch.

Connect the center pin of the switch to the lifted pin.

Then connect one of the remaining pins to +5V (+ side of the capacitor, see pics below):

For a model 1:


For a model 2:


Finally connect the last pin of the switch to ground/0V (- side of the capacitor, see pics below):

For a model 1:


For a model 2:


Results:

Some Game Gear games should now display a Japanese title and/or Japanese texts when the console is set the Japanese region:


And some Master System games played with the Master Gear Converter should display a Mark III splash screen on startup:


Sources:


Sega Game Gear Maintenance Manual - August 1992 (model 1)
Sega Game Gear Service Manual - VA1 (model 2)

2 Nov 2016

Exzisus - Taito 1987 (repair log)


Uncommon hardware with 4 CPU (Z80)! This is the one screen version of the game.
It doesn't start and displays only a plain black screen.
By passing my hand on a specific area of the board I could get it to boot on the title screen with missing elements but the game was stuck:


This is typical of a floating line somewhere. With my logic probe I found one of the address lines was cut (not visible, probably under an IC). I patched it with a piece of kynar wire but saw no improvement. The RAM @C14 is dead, I put a second hand one in place (I was running out of 6116 type wide at the time) and the game started but sound was absent:


I found another broken trace on one of the data lines of the audio RAM. I fixed it with another piece of wire and sound now works perfectly.



Game fixed.