Hey guys (and ladies ?),
this is Christian from Germany. I must say I spend more time on german Arcade forums, unfortunately we have just two types of them:
A) the ones with all the newbies who ask the same studpid MAME/RaspberryPI/HowToInstallAComputer-Questions for over and over again
B) the ones with all the fu***d up old techies from the 80ies who do all this arcade repair stuff for 40 Years now and laugh at you if you ask "too obvious, simple" questions or automatically put you to group A
So then, I´m somewhere in between and I´m here to ask for some help at the relaxed and nice guys.
I must say I don´t have much electronical experience, it´s just the basics,but I am able to read and compare 1 and 1. So with a little kickstart I think I could solve the following problem.
At the moment I'm reconditioning an old Ms. Pac-Man Cab from the US. With the Cab itself and the monitor I'm almost finished (full recap of the chassis, tube swap with swap of the yoke etc.), but now I´m kind of stuck at the PCB.
What I did already to got it running:
While running the PCB on a regular arcade DC power supply I found the (hopefully final) problem: The board is super voltage senstive.
On a DC PSU I can play with the 5V voltage, I found out that PCB "starts" only at 4,93VDC, the Z80 then runs at 4,6VDC or so.
When I touch any GND point with one leg of my multimeter (well, not all the time but often) the CPU resets.
Something in the whole circuit is causing this voltage sensitivity.
What can I do to narrow this down ? I have an oscilloscope, a logic probe (just the probe, no comparer or so), a soldering and de-soldering station and an EPROM burner to test IC.
To be honest the osci and the logic probe I never really used so far, as I´m a medium-beginner fool, but I understood the basic techiques from youtube videos.
Whats´s the best way to start looking for the voltage sensitivity, for e.g. to test TTL ICs in circuit for voltage problems (not logic problems !) as I'm not interested to desolder 20 ICs to test them externally in my EPROM burner .
I´m thankful for any hint.
Bests
Banane / Banana
this is Christian from Germany. I must say I spend more time on german Arcade forums, unfortunately we have just two types of them:
A) the ones with all the newbies who ask the same studpid MAME/RaspberryPI/HowToInstallAComputer-Questions for over and over again
B) the ones with all the fu***d up old techies from the 80ies who do all this arcade repair stuff for 40 Years now and laugh at you if you ask "too obvious, simple" questions or automatically put you to group A
So then, I´m somewhere in between and I´m here to ask for some help at the relaxed and nice guys.
I must say I don´t have much electronical experience, it´s just the basics,but I am able to read and compare 1 and 1. So with a little kickstart I think I could solve the following problem.
At the moment I'm reconditioning an old Ms. Pac-Man Cab from the US. With the Cab itself and the monitor I'm almost finished (full recap of the chassis, tube swap with swap of the yoke etc.), but now I´m kind of stuck at the PCB.
What I did already to got it running:
- swapped the 6 2114-RAM-ICs to new ones
- tested and reflashed the EPROMS
- built a new ribbon cable for the cpu board
- repaired the board connector with a new fingerboard
- changed the opposite edge connector to a new one (cause I thought I had some voltage problems)
- swapped severals caps and IC in the AC-to-DC-conversion circuit section ( cause I thought I had some AC voltage problems). I measured everything, I can say for sure now that I got 5VAC running
While running the PCB on a regular arcade DC power supply I found the (hopefully final) problem: The board is super voltage senstive.
On a DC PSU I can play with the 5V voltage, I found out that PCB "starts" only at 4,93VDC, the Z80 then runs at 4,6VDC or so.
When I touch any GND point with one leg of my multimeter (well, not all the time but often) the CPU resets.
Something in the whole circuit is causing this voltage sensitivity.
What can I do to narrow this down ? I have an oscilloscope, a logic probe (just the probe, no comparer or so), a soldering and de-soldering station and an EPROM burner to test IC.
To be honest the osci and the logic probe I never really used so far, as I´m a medium-beginner fool, but I understood the basic techiques from youtube videos.
Whats´s the best way to start looking for the voltage sensitivity, for e.g. to test TTL ICs in circuit for voltage problems (not logic problems !) as I'm not interested to desolder 20 ICs to test them externally in my EPROM burner .
I´m thankful for any hint.
Bests
Banane / Banana
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