carpent@SRC.Honeywell.COM (Todd Carpenter) (08/15/90)
Yep. Me again. (Condensed version of woes. So far I only received a couple
replies... )
Upon returning home from a three day trip, I discovered my Amiga un a rather
unworking state. The machine would not boot, and did not even get to the
point of checking the keyboard. A black screen persisted (Once I got a
purple screen).
Upon testing, pulling cards, etc., I finally located a *possible* cause of
the problem. Or it might be a symptom. Resistor R914, which looks to be a
current limiting resistor to the keyboard, is toasted. Like, as in, the left
half (facing the front of the Amiga) of it is a charred husk, and that left
post is melted all the way through.
Removal of the motherboard from the box, and examining the underside shows
that the plastic shield melted through, and the post was _possibly_ touching
the RF shield. The only thing I can think of is that the wire was too long,
poked through the plastic, started arcing to the RF shield, and eventually
the heat buildup trashed the resistor.
My problem: What other causes are there? A short in the keyboard should
*not* cause this sort of thing (that is why that resistor is there in the
first place!)
What is the value of the resistor? The schematics only say .5W, whikch would
result in a 50 Ohm resistor to handle a short. However, the resistor now
reads 1 Ohm, and I certainly can't read the thing, since it is all charred
beyond recognition.
Are there important traces in that area of the motherboard? About a 1cm
diameter area is heavily heat damaged. Any chance something could have
melted and caused shorts between layers?
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