1/1/2023 0 Comments Double dragon advance spritesJust a note for future reference : there are five TMM2018 (6116 equivalent) sprites RAMs and they are and on VIDEO board.You know, I'm still feeling too many adverse effects from having too many 3D platform games where I collect things thrown at me. PCB 100% fixed and another one preserved! So I kept to check the OBJECT circuitry until I come across the TMM2018 SRAM which had four silent DATA lines (PIN14-PIN17).I piggybacked it and magically all sprites were restored: I thought my job was done but I was wrong since this improved the sprites but not fully restored as they still missed some lines symptom of missing DATA: The 74LS86 had stuck outputs and these are tied to some ADDRESS lines of a TMM2018 SRAM which had some silent DATA lines, too.So I prontly desoldered them and they failed once tested out-of-circuit: So, following the schematics I checked this part of circuit and all was fine until I came across to this section: This a common fault on all Double Dragon PCBs since object generation circuit is wide and made of many components (it occupies five sheets of the. Once replaced it I got no more WORK RAM error and strange behaviours, game was playable but all sprites were missing: So this meant that CPU was undergoing a request of interrupt from external devices (an interrupt is a signal to the processor emitted by hardware or software indicating an event that needs immediate attention).As you can see from the above schematics these two signals are generated by a 74LS74 so for first I went to check it and I found missing CLOCK and CLEAR signals input on PIN3 and PIN13 respectively.In particular CLOCK on PIN3 is the VBLANK signal and this is generated by a NAND gate of a on VIDEO board :Ĭomparing it in-circuit revealed it was faulty: Other times it booted into game but sprites were missing, could not coin up, screen was unstable and speed was kinda accelerated.When I got this strange behaviours, the fist thing I check is the main CPU, in this case an Hitachi HD63C09.Probing it I found that PIN2 and PIN4 were stuck LOW, they are respectively the NMI and FIRQ interrupt lines: Original part is a Fujitsu MB7114, pretty impossible to find nowadays so I opted for a 82S129 which an equivalent one.After burned the device with the correct file supplied by MAME, I powered on the board and some times it got stuck on RAM/ROM TEST showing error on WORK RAM: I had this PCB since many years, honestly I couldn’t remember when I got it or where.The only sure thing is that it was faulty.Condition was pretty good for a such ‘aged’ board but it was missing a BPROM as you can see:
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