Re: Gottlieb SYS80B power question

Hi Sean,

"sean" <> wrote in message

I've decided to be "nice" and try to fix a coworkers Sys80B machine and
hopefully learn something in the process (since I've never worked on a
sys80 before)

The CPU isn't booting. Z11 literally had the top of the chip blown off
it when I received it, so I removed it since the CPU can boot w/o it.
The board is perfectly clean - ZERO acid damage as the previous owner
had removed the battery. I've pulled the CPU board out of the machine
and am benching it with a power supply (slam mod has been done). When
I hook +5.1v up to A1 pin1 and Ground to A1 pin4, the voltage across C1
is reading low at 4.1v. Heck, the voltage coming in at the board is
now reading 4.1v. The points on U1-40, U4/5/6 pin 34 are all showing

I unhooked the + side of C1 hoping it was a bad cap, but same results.
Any ideas what could cause a 1v drop immediately coming into the board?
Because Z11 was blown, I'm thinking that U4 may need replacement as
well but don't want to replace that until I fix this power thing first.
Would it just be easiest to replace the entire reset circuit? Any
advice would be most welcome. Thanks, all.

I presume you know about the system 80 documents at If
not, there is a good guide on diagnosing the system 80 control (cpu) board,
step by step at this link: Please
read this document. It will tell you what to replace. Do you know if you
are gettting a clock signal from the crystal? I really wouldn't replace
anything on that board (other than Z11!) until you know what kind of
functionality the board has, using your logic probe or oscilloscope, while
it is powered up on the bench. The reset circuit may be just fine,
especially if there is no corrosion from a leaking battery.

That is a mighty nice gesture of yours, offering to take the plunge on a
system 80 for a coworker of yours! Welcome to the illness, you will not
regret the infection!

Good luck,


Relevant Pages

  • Re: HELP: Allied Leisure Cocktail PCBs (aka John Robertson, are you out there?) - LONGish
    ... Unlikely that the Reset circuit is bad on all three boards. ... Check if the Reset signal is getting to the CPU. ... 872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) ...
  • Re: Renesas R8C Start up problem
    ... Reset circuit is only pull-up. ... CPU doesn't start up right. ... External oscillator doesn't run when I turn on power. ... the built-in reset circuit in R8C/11 and /13 is designed to operate at +5V - check is parameters in the data sheet. ...
  • Re: TECH: what the hell is going on with my sys80 CPU!???
    ... You have to understand that you can NOT simply ground Pin 40 (or whatever the CPU reset pin is - for other CPUs than the 6502 here) as the related Reset circuit often is a bit unforgiving of that sort of torture. ... note that from the schematic the 5101 and the CMOS devices get their power either from the battery or from Vcc through an isolation diode and thus would be up to 0.7VDC less than Vcc depending on current draw. ...
  • Re: Renesas R8C Start up problem
    ... Reset circuit is ... >CPU doesn't start up right. ... Put a cap between pull up and ground. ... Are all parts (pull-up, cpu and external oscillator) on the SAME power ...