Mar 262016
 

Bought on Ebay this cheap untested Double Dragon original PCB:

Double_Dragon_PCB

Board came in not very good shape, CPU board was really dirty as you can see from picture above.I powered it up and got a solid black screen so I decided to washed it.After dried and removed the oxide from JAMMA connector :

Double_Dragon_PCB_washedì

I powered the board again and this time it successfully booted  but after started a game I noticed some sound FXs were wrong, replaced only by some noise :

Sound FXs are generated by two MSM5205 ADPCM chips which read data samples from two 27C512:

ADPCM_circuitry

The two MSM5205 were tested good on all pins and piggybacking them didn’t change nothing but when I went to test the two 27C512 I found that pin 7 (address line 4) of the one @IC95 was silent so it wasn’t being addressed.Schematics showed it connected to pin 3 of a 74LS393@IC61 :

27512@IC95_74LS393@IC61:

Jumpering the two pins fixed the issue and all sound FXs were restored but it was an ugly solution so I followed the trace until the point of its break.This lead me under the socket of the 27C512 @IC95 where a pad was corroded and lost contact to pin 7 of this EPROM.I restored the connection with a piece of AWG30 wire after breaking the plastic of the socket in order to reveal the pad:

RSCN2560

Another arcade PCB preserved!

 Posted by at 7:05 pm