Diagnosing a non-working Mac Performa 476?

From: Christopher Smith <csmith_at_amdocs.com>
Date: Mon Jun 3 10:17:08 2002

> -----Original Message-----
> From: Brian Chase [mailto:vaxzilla_at_jarai.org]

> When I power up the system, with monitor attached, the
> internal cooling
> fan spins up, the hard drive spins up (and sounds normal), and the
> machine chimes what I seem to recall as being the regular
> start up sound
> for this era of Mac. However, the display remains dark. If
> I power off
> the Mac, leaving the monitor on, the monitor makes a light
> static/crackle noise; it's the sort of sound I normally
> associate with a
> monitor that's lost the video input signal. I've played with the
> brightness and contrast controls without any success.

Would you believe that the whole thing may be working? ;)

First thing to do would be re-initialize the "parameter RAM." Hit
command-alt-p-r on power up. (I have seen corrupted PR cause this
kind of problem.) There are also a couple of things that you can
(very safely) reset with other hot-keys. You'll have to look them
up, though.

You might check to see if there's any flash or what not on the monitor
when the computer comes on. If the monitor has a power-save mode, and
starts up that way, does it turn on at all?

... but now that I read the next paragraph :)

> If I switch the other monitor, the behavior is the same. If I switch
> from the orginal motherboard to the one I purchased on eBay, the
> behavior is the same. It's possible both monitors are bad and/or both

Very strange. What's common between the two boards? Do you have, or
can you get, a known-good monitor?

Are you using the same RAM in both boards? That could be suspect. If
you've been plugging the drives back into the board, don't. Take
everything out -- including un-used cables -- except what's absolutely
necessary. Try again that way.

> motherboards are bad. I don't have a multimeter to verify that the
> voltages coming out of the PS are correct. Nor do I know

This is also a problem. Just a stab in the dark, try blowing the board
out. I've seen some strange dust-bunny related problems with macs. :)
Make sure there's no way the board can short itself out to ground
somewhere...

... and get a multimeter.

> that the hard
> drive is functional--but I'd assume that nothing needs to be
> loaded from
> the HD in order to get the display to come up.

Nope, but again, take it out, and the floppy, and whatever else (boards,
etc) you can. Bad hardware makes computers do funny things.

> I'm a bit puzzled, and wondering if anyone here with insight on these
> Macs and their displays can give me any additional pointers.

Err -- you could also get an adaptor to plug a vga monitor in, and use
a monitor you know works, to eliminate that possibility.

Chris


Christopher Smith, Perl Developer
Amdocs - Champaign, IL

/usr/bin/perl -e '
print((~"\x95\xc4\xe3"^"Just Another Perl Hacker.")."\x08!\n");
'
 
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Received on Mon Jun 03 2002 - 10:17:08 BST