Arcade PCB Repair Logs

Arcade PCB Repair Logs #1: Tekken (Namco System 11)

Let's start off nice and easy. 

Tekken is a fighting game using the Namco System 11 architecture, which is similar to the Sony Playstation. The PCB consists of a mainboard, a CPU board and a daughterboard with mask ROMs. Note that the CPU board is interchangeable with other System 11 games, but the mainboard and daughterboard are not. The mainboard holds the program ROMs, and the daughterboard holds the graphics ROMs. This board looks good, at least before you plug it in.

 

Symptom #1

The board would boot, but there appeared to be a lot of missing graphics.

Resolution:

Because a few items seemed to be jumping on screen and disappearing, there was a chance of a loose connection somewhere on the board. Using a non-conductive implement, I started pressing down on various surface mount chips on the CPU board. I found that pressing down on an SRAM chip restored some graphics. Without applying pressure, I checked the pins using my logic probe, and found that many of them were not registering a signal at all. I then used my hot air gun (flow and temperature adjustable, from www.mcumall.com) to gently reflow the solder around that chip, while pressing down on it with a heat resistant tool while the solder solidified. Graphics were restored somewhat.

Symptom #2:

Video still seems washed out and backgrounds appear white in some cases.

Resolution:

Even with the SRAM chip now firmly connected, I compared my video with an emulator and found that everything seemed too bright. Hunting around the CPU board I found a small potentiometer labeled "VIDEO LEVEL". I turned down this pot and the image came back into balance. The backgrounds were present since the SRAM chip was fixed, but just over saturated up into pure white.

Lessons learned:

Surface mount chips are not impervious to weak solder joints!