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
3.63v.

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 www.marvin3m.com? If
not, there is a good guide on diagnosing the system 80 control (cpu) board,
step by step at this link: http://marvin3m.com/sys80/index3.htm 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,
Dan


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