On 20 Mar 2005, at 10:03, Edwin P. Groot wrote:
Hello all, this is my first post as I'm new to the list.
Welcome!
I found in the trash a fat Mac that gives a checkerboard pattern when
the power is applied. There is no startup tone audible. The pattern is
about 15 squares wide and 40 squares high. Any ideas on repairing the
problem (besides buying a Macintosh 128 logic board)? Here is what I have
tried so far, after Googling:
Pull the RAM and ROM chips and upgrade card (see below), and reseat
them (in correct orientation, of course). Same checkerboard.
That's always a good place to start.
Replace the 2 banks of 1256-15 chips with known good 1256-12 chips.
Same checkerboard.
Replace the 2 banks of 1256-15 chips with known good 1256-10 chips.
Vertical stripes.
Replace the 2 banks of 1256-15 chips with known good 164-12 chips.
Blank screen.
Quick power off, power on cycle. Same checkerboard, but a few pixels
reversed.
On opening the Mac, I discovered that this was a Macintosh 128 that
had been upgraded to 512K. The upgrade appears to entail: replacing the
old RAM chips with sockets, plugging 1256 chips in the sockets, replacing
one TTL chip with a socket, and plugging a small circuit board in the
socket. The identity of the TTL chips on the small circuit board has been
unfortunately wiped off. Logic board is clean, and voltages to the logic
board seem OK. I found ca. 2.5V, 5V, +-12V and ground on the wires.
Eek! Debugging an upgraded board like that is always going to be a pain.
Personally, if the display is sharp, and there's no bad screen burn, so it's worth saving the Mac, I'd go for the replacement logic board route. A 128Kb board would be nice and authentic; a 512Kb board would be cheaper, and more useful!
If you can't find a board in Germany, contact me in the second half of April, and I could probably find a 512kb board in my garage and ship it to you for the cost of postage. (I'm in the UK)
best wishes,
Stuart
-- Compact Macs is sponsored by <http://lowendmac.com/>.
Support Low End Mac <http://lowendmac.com/lists/support.html>
Compact Macs list info: <http://lowendmac.com/lists/compact.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:compact.macs@mail.maclaunch.com> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive:<http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/>
--------------------------------------------------------------- iPod Accessories for Less at 1-800-iPOD.COM Fast Delivery, Low Price, Good Deal www.1800ipod.com ---------------------------------------------------------------
