carpent@SRC.Honeywell.COM (Todd Carpenter) (08/10/90)
I was away on business travel and upon arriving home, I found my Amiga in a
rather toasted state.
My configuration:
A2000, Rev 4.3, with resistor upgrade to 4.5
A2090a
A2630
various hard drives and a modem
Symptoms:
Screen was dead
Vulcan neck pinch didn't do *anything*
power cycling didn't help.
keyboard didn't flash on reset, nor did the screen flicker - it stayed black.
Once, I did manage a purple screen.
Since I wasn't getting anywhere, I began dismantling things, attempting to
locate the problem. I finally discovered that without the keyboard plugged in,
it would actually attempt to boot. (Since I don't use workbench, I didn't get
any further than that). So, with keyboard plugged in, *nothing* happens.
Without it, a normal powerup sequence commences.
I took the keyboard apart, and didn't see anything of interest. No toasted
components or anything. No, I did not yet take apart the actual keyboard
assembly.
I took the power supply and drive assembly off the motherboard, and loe and
behold, resistor R914, to the left of the keyboard port, was smoked. Looking
at it from the front of the Amiga, the left side of the resistor was all black
and twisted, with burn marks on the circuit board and the large capacitor right
next to it. Gentle pushing of the resistor indicates that the wire is burned
through on the left side, so it is no longer even making contact with the
board.
Examination of the 2000 schematics reveals that this resistor is probably a
current limiting .5W resistor to power the keyboard. It shouldn't be a big deal
to replace it, assuming the circuit board traces are still recoverable.
However, what on earth could have caused this? Spontaneous resistor breakdown?
Microfractures in the wire, resulting in small arcing, eventually leading to
breakdown? There were no users on the machine when this happened, and I have a
surge protector that I know works (It trips out when even the clocks in the
house don't die). The room is fairly humid, so it wouldn't be a static
buildup. I'd hate to replace the resistor, and then have a chip blow because I
have a short somewhere in the system, and I just reestablished power to it...
Suggestions? Please? email is preferable...
(Oh, *yes* I am the guy asking for keyboard extension ideas. *NO* I have not
tried anything yet, so that is not the cause of the problem. Unless the Amiga
reads the news messages that I post...)
Todd P. Carpenter Honeywell Systems and Research Center
voice: (612)782-7229 paper: 3660 Technology Drive, Minneapolis, MN 55418
UUCP: carpent@srcsip.uucp bang-style: {umn-cs,ems,bthpyd}!srcsip!carpent
Internet: carpent@src.honeywell.com or Arkon%kryl@src.honeywell.com