Hishou zame pcb repair

[sukhbir]

Got hold of this recently from a member who asked me if i can have a look at it.The pcb is called Hishou zame which is the japan release of flying shark.I was informed that the game used to work until accidently the jamma loom shorted something on the pcb .
Before frying it up i first did a resistane check on the jamma edge and compared the readings with my working pcb.
The reading on the +5v,+12v rails were approx the same as on my board so that tells me there in no short circuit .
ok now to fire it up and do a smoke test ,pcb did not boot and was dead .There was no obvious components getting hot except for the custom cpu (C-01) which normally runs hot all the time.
The next step was to check the activity on the 68k cpu.
RESET HI
HALT HI
DTRACK HI
ADDRESS HI
DATA HI
CLOCK FLOATING.

Now without a clock input to the cpu it will do nothing,so next to see if the main crystal(28MHZ) is pulsing.
Check was done on the crystal and i had signs of life with good pulse.This pulse goes to pin 2(H1) of the ls163(counter) and worked out the clock pulse comes out of pin 13.
the output from pin 13 of the ls163 goes to the input of the ls04(F2) pin 11. The output cpu clock pulse comes out of pin 10 and i got a floating signal on my scope,removed the lso4. fitted socket and new ls04. fired it up and i got cpu pulse but the game is still dead☹️.The clock input to the cpu was still floating so there must be an open track someware.comparing my pcb i found the open track,there are 3 custom chips marked L-01 and the top ones trace was open from pin 1 to pin 1 on the 2nd one down.Soldered a piece of kynar wire and fired it up.

oh yes ,another one saved from being scrapped,played this awsome classic and all was good.

 

[TheDaddy]

Wish I was this lucky with my Simpsons !!

Nice repair,

Dave.

 

[Retroman839]

Man! Well done😎
Did you check continuity between the L-01’s ? Pin to pin on each trace systematically until you found the short ?

 

[sukhbir]

The L-01's and some other logic chips were all daisy chained to the output pin 10 of the ls04.
From pin 10 of the ls04 to the top L-01 it had continuity but the one just below was infinite resistance.

 

[Retroman839]

Is this the clock?
Timing form the crystal ?
Or is pin 1 vcc?

 

[sukhbir]

The output from the ls04 pin 10 is the clock frequency for the 68k cpu and customs, I haven’t measured the frequency but I guess it’s around 8mhz.

 

[Retroman839]

Is this the clock?
Timing form the crystal

The output from the ls04 pin 10 is the clock frequency for the 68k cpu and customs, I haven’t measured the frequency but I guess it’s around 8mhz.

 

[Retroman839]

Very interesting.
Is the resonance from the crystal up and down like a sign wave?

Is this the timings for the clock of the cpu ?

 

[sukhbir]

All crystals on arcade pcbs generate a specific frequency in the form of a sine wave usually at TTL level.
Cpu’s all have a clock inputs to determine its operating speed.
hope that makes sense

 

[Retroman839]

It makes sence 👍