Hi all,
I've finally found the glitch in my Jupiter Ace. When the power supply
was momentarily reversed (and applied to the I/O port), the CPU (a NEC
D780C) and one of the RAMs (NatSemi MM2114) packed up. After replacing the
CPU with a spare (OK, I pinched it out of a Toshiba HX-10 MSX), I've managed
to perform a bit of testing. With the CPU out, everything looked good. When
I powered up and probed all the data and I/O lines, D7 was locked to 0V and
D6 was sitting at around 2.5V. Obviously, something was overloading the
Z80's data bus, causing it to overheat significantly. After removing the RAM
(and nearly pulling up four pads), the Z80 seems to be running fine. RFSH is
pulsing, as are M1 and CLK. The data and address lines look OK on my scope,
too.
So, it looks like the Z80 bit the dust when the PSU touched the I/O
port, then it proceeded to dump 9V into D6 and D7. After that, it let out
the magic smoke. Thankfully both ROMs (TMS2532s - TI's clone of the 2732)
seem to be OK.
The only "interesting" thing is that the current draw is around 500mA
with everything except one of the RAMs and the CPU fitted. With the CPU (a
Sharp LH0080A) fitted, the current consumption rises to approx. 620mA. Can
someone with a working Ace please check the current consumption of their
unit for me?
Later.
--
Phil.
philpem_at_dsl.pipex.com
http://www.philpem.dsl.pipex.com/
Received on Fri Dec 06 2002 - 13:02:01 GMT