Oct 292016
 

Yes, yet another Double Dragon PCB on the bench.

The board was in good shape:

100_8956

but it didn’t pass the self-test sitting on a ‘63701 ERROR:

100_8959

The /HALT line of the HD63701 MCU was asserted, this was sign of some trouble in its busses.I swapped a good chip with no change so I went to look at schematics.All was good until I found no continuity between the address line ‘A0’ (pin 50) of the MCU with pin 3 of the 74F157 @IC8:

hd63701_bus

Tracing back the address line I could figure out where connection was  interrupted, exactly under the 74F157 @IC7 so I removed it.Inspecting the involved area with a USB microscope revealed a corroded trace  :

bad_trace

I patched it with some AWG30 wire:

100_8979

With this fix finally the board passed the self-test but two issues were present in game : sound was missing and backgrounds had jailbars :

The first issue was due a missing 10Kohm potentiometer in the sound section:

100_8981

The backgrounds GFX data are stored into four 27512 OTP devices on video board :

bg_romsjpg

When I went to dump the ones @IC108 ans IC109 my programmer warned me about a bad contact on pin 19 (data line ‘D7’) of both :

 

27512ic109

Obviously the resulting dumps didn’t match the ones from MAME ROM sets so I programmed two 27C512 EPROMs as replacement.This restored graphics completely.Yes, yet another Double Dragon PCB fixed!

 

 Posted by at 11:46 pm