lac@ecs.soton.ac.uk (Les Carr) (06/25/91)
Our MacIIci has developed a monitor problem: after a couple of hours being left on (usually happens overnight) it switches itself off. The Mac itself remains active, and by a lucky stroke I managed to choose "Shutdown" from the "Special" menu without any display. Because power-cycling the monitor doesn't have any effect, it *looks* as though its the Mac's fault (How does it switch the monitor off at shutdown?) but we don't see this behaviour when we swap another monitor onto the mac. The repair company can spot no fault (as usual). Has anyone seen anything like this? -- L.Carr@ecs.soton.ac.uk Les Carr Tel: +44 703 593649 Dept of Electronics and Computer Science Fax: +44 703 593045 University of Southampton SO9 5NH England
steveh@tasman.cc.utas.edu.au (Steven Howell) (06/25/91)
lac@ecs.soton.ac.uk (Les Carr) writes: >Our MacIIci has developed a monitor problem: after a couple of hours >being left on (usually happens overnight) it switches itself off. >The Mac itself remains active, and by a lucky stroke I managed to choose >"Shutdown" from the "Special" menu without any display. >Because power-cycling the monitor doesn't have any effect, it *looks* as >though its the Mac's fault (How does it switch the monitor off at shutdown?) >but we don't see this behaviour when we swap another monitor onto the mac. >The repair company can spot no fault (as usual). Has anyone seen anything >like this? >-- >L.Carr@ecs.soton.ac.uk Les Carr >Tel: +44 703 593649 Dept of Electronics and Computer Science The monitor sounds like the standard sony apple colour display.. This fault is a real dabster, it even had me hunting for hours, i think its been mentioned on the net before, and i can almost be certain it will be mentioned again... anyway.. the fault lies in the high voltage capacitor assy. this capacitor acts as a filter for the EHT voltage, and slowly breaks down due to age, This causes excessive current to be drawn by the eht transformer, and thus causes the horizonal drive circuit to shut down, in attempt to protect itself. However, buy simply replacing the capacitor,it will fix the problem. Basically, the power/sweep board reports back to the switchmode a fault of mass destruction is about to occur (the cap is about to short or arc out or the eht transformer or transistor just kicked it) , and thus the power supply shuts down all outputs. The capacitor is located just underneath the end of the tube, attached to the bottom of the monitors metalic internal case. Its is vivid red and has 2 large red high voltage cables extruding out along with 2 other feed back cables. The cost of this cap is approx $85.00 Australian.. so what ever that is where you are... anyway, good luck i hope this fixes your monitor, but remember, always take it to a qualified apple tech, I have seen one guy totally butcher this model monitor looking for the fault, he even removed the protection circuit to get it going.. steve h
todd_strauch@med.umich.edu (06/26/91)
In article <8284@ecs.soton.ac.uk> lac@ecs.soton.ac.uk (Les Carr) writes: >Our MacIIci has developed a monitor problem: after a couple of hours >being left on (usually happens overnight) it switches itself off. >The Mac itself remains active, and by a lucky stroke I managed to choose >"Shutdown" from the "Special" menu without any display. > >Because power-cycling the monitor doesn't have any effect, it *looks* as >though its the Mac's fault (How does it switch the monitor off at shutdown?) >but we don't see this behaviour when we swap another monitor onto the mac. > >The repair company can spot no fault (as usual). Has anyone seen anything >like this? >-- > Our department has a color monitor in to our repair facilities for the exact same reason. Service personnel claim to find no problems and suggested we bring in the chassis that went with that monitor. I don't feel that it will do any good because the monitor has been on three different machines and exhibits the same problem. The original chassis has had two other monitors on it with no problems. I currently feel that it is a heat problem with a component in the monitor. The cooler the monitor is kept, the longer it takes for it to shut itself off.
kaufman@neon.Stanford.EDU (Marc T. Kaufman) (06/26/91)
In article <8284@ecs.soton.ac.uk> lac@ecs.soton.ac.uk (Les Carr) writes:
->Our MacIIci has developed a monitor problem: after a couple of hours
->being left on (usually happens overnight) it switches itself off.
->The Mac itself remains active, and by a lucky stroke I managed to choose
->"Shutdown" from the "Special" menu without any display.
->Because power-cycling the monitor doesn't have any effect, it *looks* as
->though its the Mac's fault (How does it switch the monitor off at shutdown?)
->but we don't see this behaviour when we swap another monitor onto the mac.
->The repair company can spot no fault (as usual). Has anyone seen anything
->like this?
We've seen posts like this before, and the problem has happened to me, so
maybe the answer should be in the FAQ list.
A probable cause of this behaviour is failure of the high voltage multiplier
assembly -- either the diodes or (more likely) the capacitors. Replacing
the entire assembly (it is a single piece) is the way to go.
Marc Kaufman (kaufman@Neon.stanford.edu)