"robb" wrote in message
...
"robb" wrote in message
...
i have a micro-controller board with 3 big 40DIP ICs, 10 or so
16
DIP support ICs. with 32v/8v/5v transformer supply that
connects
to two bridge rectifiers {32v, 8v}a fuse links sit between
transformer and rectifiers, no schematic.
i believe the 32v shorted with 5V line all
three fuses blown.
So....where does one start to diagnose such a *big* problem ?
Thanks to all who have helped in the past too many to name ..
seems my sacrificial chips so far were the MCU (8031) and ROM
chip (TMM23256) 
(((((( very sad
Synop:
--------
microcontroler board , 32v and 5v rails meet. a single snap
later and she is dead.
5v rail to 0v rail shows 63 Ohms and should probably be about 400
Ohms
To diagnose using advice fom *s.e.b*
removed the power regs, made a 5 Volt 1A power supply,
connected to 5V and monitored current (~450 milliAmps) and
monitor heat on all components
Nothing really panned out here, no heat or crazy current
So i removed the MCU (8031) and the super important ROM chip
(TMM23256P) and the Ohms jumped to about ~456 Ohms and the
current was down to ~ 275 milliAmps. so those must be the
sacrificial chips and of course the measured Ohms of the ROM
Vcc to Vgrd was 72 Ohms very sad : ..... ((
so i put the 5 volt Reg back and powered up then added fuses for
the 36 volt line and no fuses blown so now i need to get a new
8031 replacement and a ROM chip and of course the ROM IMAGE ((
Semi-Good News...
i have access to a a similar main board (an upgraded one
actually) but it has a 8051 MCU with on board ROM and not
external ROM
so my choices now are
A. get an 8051 and copy the ROM over and install maybe that will
work ?
B. get a 27c256 ROM chip and a 8051/8031 with or w/o ROM then
force external memory use pin to appropriate setting and copy
the borrowed 8051 ROM memory onto the 27c256 ... hope that works
Any advice here and ideas are highly welcomed as i do not want to
cause even more troubles
thanks to all that have helped so far,
robb
I think that it would be a good idea to restart this thread at the top of
the list again, as it is now a long way down. The only way that I knew that
you had posted again, was that I still had a 'watch' set on, that I had
forgotten to remove. Just as a matter of interest, have you actually tried
sticking the ROM (I take it that it's a standard 27 series EP-ROM ?) into a
PROM blower just to see what it makes of it? They usually do an evaluation
of the chip first, and will put up an error message regarding what, if
anything, they find wrong. 72 ohms does, I agree, seem a bit low though.
Have you compared this figure to a known good chip ? Remind me again what
the board is out of. Is there absolutely no possibility of finding another,
even if still in service, anywhere in the world? The 'net is a very powerful
tool in this regard.
Arfa