A said, the board was not properly working since on power up it was stuck on a static screen on which you could insert coin but nothing more :
Main (and SUB) CPU is a NEC V30 (real part name uPD70116)
Probing it revealed that HALT pin (active HIGH) was asserted hence the CPU stopped its processing putting its busses into a high-impedance (or tri-state if you want) state :
The main CPU uses four 8k x 8-bit static RAMs:
Probing them with a scope revealed weak signals on data lines of the ones @U028 and U021, here's a comparison with an healtly signal on the left of the below picture :
This and the fact that RAM chips were Toshiba TMM2063 (so very prone to failure) lead me to remove them :
Both chips faied the out-of-circuit testing :
Installed sockets and fresh RAMs :
I powered board up and it booted into game with no further issues.Repair accomplished.
Hi Caius,
ReplyDeletecongratulations on the new site! Quick question on desoldering the RAM in this repair. From the leftover solder it looks like you used hot air? Could you do a write up on the techniques that you use?
Sorry for late reply.For desoldering ICs (especially big ones) I use this technique (video is from mine while I remove a Konami '054986A' audio module) :
ReplyDeletehttps://www.youtube.com/watch?v=Y6WxU9QiiIo