Technos Double Dragon 2 arcade pcb repair
I got a very clean original Double Dragon 2 pcb, but unfortunately it was completely dead. No video output at all, and a logic probe revealed almost zero activity on the TTL chips. After checking voltage, the first thing to do in this case is to check if the CPU is getting a clock signal – and indeed the clock pins were completely dead.
On both Double Dragon 1 & 2 the main CPU clock comes from a 12MHz crystal on the video board. Probing around here again showed no activity so a suspicion is the crystal itself was dead. Before replacing it though I checked the Double Dragon 1 schematics which showed a capacitor should be present and none was on my board. It seems the tiny capacitor that should be at C43 (C36 in DD1) had been snapped off so cleanly it just looked like an unpopulated pad.
A replacement was taken from a Dragonninja parts boards and amazingly that was the only fault – all sound & graphics were perfect.