Quartet repair log

 PCB Repair Logs, Repair Logs  Comments Off on Quartet repair log
Mar 042016
 

Here is a recently repaired Quartet running on Sega pre-system 16 hardware.

quartet1

The 3 replaced chips are highlighted in red. I will explain every step of the repair process below.

1) The game was booting to a garbled screen:

quartet2

The 74LS04 located at 1H (an inverter, manufactured by Fujitsu) had good clock signals on entry pins 11 and 13 but had floating signals on outputs pins 10 and 12. Replacing the chip changed the result on boot…

2) I then got a screen with garbled graphics but with a countdown appearing at the center.

quartet3

This is normal on pre-system 16 games. Normally, after reaching 0, the game is booting. Here, I got a black screen after the countdown.

I noticed that the reset pin on the 68000 had a square looking wave signal, which was pretty weird (it should be a linear signal at +5V). The chip that generates the reset signal is a MB3771 located at 1G (again, manufactured by Fujitsu). Probing its pins made the game sometimes booting. I replaced it by a new 3771 chip and the game was now starting normally.

quartet4

3) The game was working and playing fine except for the FM sound that was inoperative (only the voices could be hear). It was due to the YM3012 located at 1B (a DAC). It had good looking signals on its inputs but nothing seemed to get out of its outputs. After replacing it I got the FM sound back.

Now the game is fully working.

Final Star Force repair log

 PCB Repair Logs, Repair Logs  2 Responses »
Jan 062016
 

Recently got this Final Star Force PCB with graphical glitches on the sprites.

fstarforce1

This game uses a motherboard (pictured above) and has a romboard on the other side fitted with no other chips than the game’s ROMs.

All the ROMs were tested ok on my programmer and cleaning the connectors and looking at the signals, everything seemed fine with that romboard.
The motherboard has a rather simple layout with a lot of RAMs, some ASICs and a few TTLs. After a few hours looking for suspicious signals, I finally found the faulty ones.

There is a row of 12 Sanyo LM33464G RAMs (64k-word x 4-bit). Two of them were bad (the ones at IC22 and IC33). Piggybacking them with new ones partially brought back clean sprites, even if there were a few glitches remaining. These glitches totally disappeared after replacing the RAMs.
As these models of RAMs are a bit uncommon, I took compatible TMS4464 as replacement (highlighted in red):

fstarforce2

Here are before and after pictures:

fstarforce3 fstarforce4