JAMMArcade.net – Page 112

Bay Route (317-0116) tested

Decrypted Updates Comments Off

Mar 292016

Ace’ has tested the Bay Route (317-0116) decrypted set and report it works fine.
Thanks to Ace’

Megazone repair log #1

Mar 292016

Got a very clean Megazone pcb for a repair. The board was in near mint conditions but it didn’t boot and also the Sync was missing.

Looking at the schematics available online, I noticed that the quartz responsibile for the CPU clock and sync was the one placed on the bottom board.

Tested with my frequency meter and it was dead.

It is a very rare 18.432mhz OSC which to my knowledge is used only by early 80s Konami boards.

megazone

Luckily I had a Double Dribble which I used for spare parts which had the very same OSC.

After changing it, the game booted perfectly.

megazone3

megazone4

For you information, if you try to install the more common 20Mhz OSC, the colours are off and the scrolling is jumping often, so unfortunately it’s not a good replacement.

The board had no sound but I immediately noticed that there was no noise coming out of the speaker which is the evidence of a faulty amplifier.

The amplifier is infact the very unrielable LA4460N, so after confirming the the music could be hear on input pin 2 , I exchanging it and fixed completely the game.

megazone2

Today I’ve dumped the PALs from a World Rally PCB.Board has five PLDs but I could successfully dump two of them since the other three are registered.Original devices were two TIBPAL20L8 which I reversed and tested fine onto GAL22V10.

Double Dragon repair log #8

PCB Repair Logs Comments Off

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_washed ì

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