Spiderman and GTB knowledge

[Retropin]

Im sure most here will agree that a major part of fixing a machine is knowing the little nuances and caveats of the system. Without this knowledge, fixing a game can be a real head scratch.

Im getting a sys80 Spiderman up and running. After rebuilding the power supply and doing all the grounding mods that are a requirement for these games, i had some faults.

Mainly, game would boot and go into attract mode - could get credits to register but as soon as the start button was pressed or diagnostic button, game would blank out, displays go down and everything would freeze up.

Looking on Clays site, my main focus was on the slam switches or grounding of the coin switches. I tested and tested these over and over, tested the 4148 diodes again and again, followed looms and signals etc, but nothing worked.

Then late last night, i noticed that the 4 chips that sit together on the CPU had 3 replaced. Obviously, there had been a fault here before.
The 4th chip was a straight TTL 7404 - the 3 that had been replaced were the Scottky version - 74LS04.
Now, if i remembered correctly from my TAFE days, you cant always use an LS where straight TTL is used.

So today i replaced the 3 chips with straight TTL 7404 - and we have success!!! Ive just played my first ball on Spiderman - albeit with 2 coils down.

So, a little sys80 game knowledge that i will lock into memory - only use straight TTL chips, any others cause strange  faults to occur

[ajlaird]

Yeah, that's the sort of thing that makes sites like these invaluable. Thanks for sharing.

[Strangeways]

Good stuff Gavin... Most would not have even bothered to look there - I would have looked in other places..

so does it play ok ?

[Marty Machine]

Aahhh the old Low-Power Schottky fan-out limitations strike again 

Well found!, that woulda stumped many a great tech, i reckon you would have completely bypassed this had all 4 chips been LS04's...an head scratched for another year over it 
As a matter of interest, hopefully the manual shows 7404 on schematic and NOT LS04's ???

In desperate times, you could piggyback solder another LS04 on top of the existing one to 'buffer it up'.

Glad you found it the easy way though 

MM.

[Retropin]

Your right Marty,

Had the previous owner replaced ALL 7404's i wouldnt have had the light come on so quickly.

But tell the truth,. it was getting to the point where i was prepared to "shotgun" the circuit and replace all components. I knew that a chip was out of spec or a connector flakey, as you could see the machine TRYING to give you a game, then just crashing

Ive no doubt, the manual will say 7404, but i dont have it, nor do i have a schematic. Guess i could have saved time with one though...

[Marty Machine]

A VERY lucky man