Board was in good state and marked with a "OBJECT RAM ERROR" label :
But actually I got only a black screen when I powered it up./RESET and /HALT lines of 68000 main CPU were stuck LOW, no proper transition to HIGH state .
The /RESET circuitry is a typical one built around the 'PST518' voltage detector IC plus all parts needed by its typical application circuit (resistors and a capacitor) :
Like I did for my previous Demon's World repair I went to check in-circuit the ESR of the 10uf 16V electrolytic capacitor (its role is important because when the power supply voltage drops below a certain threshold, it suddenly discharges generating thus the required reset signal).It measured 9.2 Ohm, way beyond its typical value :
The capacitor was clearly bad hence I replaced it with a tantalum one :
Finally I got displayed the 'OBJECT RAM ERROR' reported by the sticker on the PCB :
I experienced this issue many times on other Toaplan PCBs so I knew where to look at.The sprites RAMs are two 6116 (2k x 8-bit) devices located just below the custom ASIC 'FCU-2' which is the sprite generator that addresses the RAMs and processes their data :
A closer inspection revealed a not perfect soldering of the 'FCU-2' ASIC :
I made a full reflow of it, soldering was now bright as it should be, sign of a good electrical conductivity :
On next power up I was greeted by this :
Board was fixed and game fully working.Another successful repair accomplished.Let's move now to the next faulty PCB in the pile!
