robb wrote:
"Eeyore" wrote
robb wrote:
i have a micro-controller board ....
i believe the 32v shorted with 5V
blew one fuse link. the fuse link was replaced with same
and when powered all three fuses blown.
So....where does one start to diagnose such a *big* problem ?
Well .... if the 5V supply went seriously high, the chances are
it's all fried. ::-(
there is a 630 mA Busman type fuses on all the lines i hope that
saved things ?
I'm afraid fuses are merely for preventing fires, not preventing damage (except
for the case of 'extreme' fuse types like the ultra-fast types).
but the fact that i am getting a short detected
between 0V and 5V line has me worried maybe thats good i do not
know hopeful someone can give me an method for finding problems ?
No, I'm afraid that's actually bad news. I assume therefore it literally 'wont
do anything' at present and any power supply connected to it goes into current
limit ?
Have you tried powering the pcb from an external stabilised 5V
power supply ?
The very first thing to look for is a clock oscillator (and
valid reset signal).
Get the data sheets for those 40 pin chips, identify which one
is the micro and scope the relevant pin(s).
What are the 40 pin chip numbers btw ?
one is the Phillips MAB 8051 micro,
OK. That's a real easy one to check AND replace (at least with a modern CMOS
version).
Data sheet here.
http://www.datasheets.org.uk/search....ub.x=0&sub.y=0
If it was working I'd check for activity (pulses/wvaeforms) on the Xtal1/2 pins,
ALE and PSEN first.
then SRM 2017 Static RAM,
OK. Not sure how easy that would be to replace.
Data here for the pinouts..
http://www.datasheets.org.uk/search....ub.x=0&sub.y=0
and NEC 8547E7 (D23256) ?? - can't find data sheet
I expect that's a 256k bit EPROM. Does it have a glass window ?
Important note. This is the most important part on the board. If it's fried so
are you. A dead EPROM will mean that the whole machine can't be repaired (unless
you can get the source file). Treat it with utmost respect.
then dual full bridge driver - L298
comparator - LM393 LM339 etc
some nor buffers and and and invertor pkgs
These are 'commodity' parts that are easily replaced. Not a problem here. First
you need to get the 'big' digital parts functioning.
General tip. Don't apply power to any high power I/O switching chips like the
L298 until the digital stuff is back to normal again.
Here are some ideas. You say you have a short across the 5V logic supply.
Firstly you need to clear that and find the cause. Are the chips socketed ? If
so it's easy to remove them and check for individually shorted chips. Check
across the power pins. Normally these are opposing corner pins like pin 20 and
40 on the 8051 for example ( or 7/14 8/16 and 10/20 on 74 series chips) but best
to get data sheets for anything unfamiliar. If you're lucky you may find one (or
two or threee) failed 'sacrificially' - saving the others but you need to find
the failed chips and get replacements for them.
If they aren't socketed now is the time to do this ! Removing ICs from PCBs
without damage is a skilled task so I would sacrifice anything that's easily
replaceable by cutting the pins at the IC body with fine cutters and removing
those pins one by one from the PCB. That way there's very little chance of doing
much damage. Be careful to fit sockets that firmly grip the leads especially if
this is some industrial controller used in areas where there's significant
vibration. That means DON'T use turned pin sockets, the pins will 'walk out' of
them.
How about you give is a complete list of the ICs on this pcb, plus make a scan
of it and post it where we can see it ? That'll help enormously.
Graham