Data East The Real Ghostbusters arcade pcb repair #2

Board was completely dead to start with – no video or audio output.  The video board from Gondomania is the same as the Ghostbusters video board so I started off by attaching a known working video board to the Ghostbusters top board.  This gave me some garbage video:

Which confirms there were faults on both the Ghostbusters top CPU board (because the software was not running) and the bottom board (because there was no video output at all).  The top board was an easy fix – the CPU was inserted backwards – luckily it wasn’t damaged and the game ran fine when reinserted properly.

To debug the bottom video board I started by examining the signals going to the connector between the two boards.  Surprisingly the video sync (CRTSYNC) and vertical blank (VBLK) all pulsed correctly on a logic probe which confirmed the video clock was working as well as the custom IC that drives sync.  The RGBBL (RGB blanking) signal though was stuck low and this seemed to inhibit any RGB output.

From there it was just a case of tracing back all the inputs to RGBBL until a problem was found – which was the HCLK0 input was stuck high.  Rather strangely this turned out to be a physical problem on the board rather than a TTL one – the leads on some of the ICs had not been clipped short enough and at one point on the board the HCLK line was shorted to a +5V line.  When cleaned up everything worked 100%.