Interesting NTDEC NROM multicart with half-of the games not working.

[krzysiobal]

shell-top.png

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top1_corr1.jpg

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bottom_corr1.jpg

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scr.png

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Uncommon thing is the reset circuit that does reset only once, at power-up and not on soft-reset
(huge capacitor is charged only on power up, not by M2).

Code: Select all

VCC ---100R--+
VCC ----|<---+--- /RESET
GND ----C----+

Something similar I found only on PEGASUS 5 in 1 multicart (Zlota 5), though without diode:
http://krzysioba.com/carts/?action=sear ... t=name_asc


256kB PRG is split between two chips (PRG1=9004 and PRG2=9005) and the logic that involves decoding signal to PRG2 uses NPN transitor as an inverter of A17, maybe that would explain that issue in half of the games:

bug1.jpg

bug2.jpg

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because 74LS32 requires quite amount of current and high level of /A17 is pulled up by 10k resistor:

sch.png

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Code: Select all

   fedcba9876543210
A~[1.....PPPvpmCCCC] $8000-FFFF
         ||||||++++-- 8kB CHR 
         |||||+------ mirroring: 0=V, 1=H
         +++-+------- PRG-bank (p ignored in 32K mode)
            +-------- PRG mode: 0=16K, 1=32K

I am also curious of internal melting of shell - was it caused during manufacturing molt injection or someone (like me) used hot-air to peel-off the old label and the heat was too much?

shell-melt.jpg

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