brant@alberta.UUCP (Brant Coghlan) (02/24/89)
A friend of mine just gave his mouse a static shock treatment. His right mouse button will not work anymore. Can anyone offer some suggestions on how to fix his amiga 1000? Some technical details might help out so here goes. The mouse it self seems to be ok. Its got to be the POT0Y line that got frazzled. This line goes through a resistor and shares a capacitor before going into Paula as pin #33. A quick test of the POT0DAT register (address DFF012) indicates that the up or down of the button is sensed, but holding down the button does not change the register as it should. All other functions seem to be ok. Could Paula have been damaged? If it is the capacitor, how can it be checked? Any help would be appreciated. Thanks in advance. -Brant -- Brant Coghlan (career student) (403) 487-3619 ...!alberta!brant Dept. of Comp. Science, 615 GSB, U of Alberta, Edmonton, Alberta, Canada
hull@hao.ucar.edu (Howard Hull) (02/27/89)
I just the other day frazzed an Amiga 1000. Here in Colorado, static electricity generation is an extreme winter hazard. I am always very careful about static electricity, having developed a number of "peculiar" habits, such as touching another person in some unrestricted part of their anatomy or touching a light switchplate or a lamp, or the finger stop on my dial telephone before handing them any electronic parts or circuit boards, even those in protective packaging. I never reach for the keyboard on approaching the Amiga without touching the desk lamp first. At work we use static mats on the floor and benches to provide grounding and to suppress generation of static charge. A wrist strap is absolutely essential when working on exposed electronic assemblies, but usually turns out to be overly restrictive in the home computing environment. I do not normally regard a well engineered microcomputer (such as the Amiga) as an "exposed electronic assembly" though. It is apparent that some care has been taken in the packaging of the Amiga to reduce the hazards associated with inadvertent static electricity generation and discharge. The EMI shield is very solid protection for most of the machine, and the keyboard has evidently been treated with a somewhat conductive coating or is made of a material that has slight conductive properties (or so it seems to my experience). On occasion I have snapped an arc to the #1 mouseport shell. This is usually a surprise considering the precautions I take, but I have done it three or four times in four years of working with my Amiga. There has never been a problem from it, though, since the shell is grounded to the EMI shield inside the machine. However, the Amiga does have an unexpected point of vulnerability. The shield provided at the plug end of the mouse is not manifested in the construction of the mouse provided with the Amiga 1000 computer. I was on the telephone when I noticed my printer was going ape on a DPaintII print-out, so I lunged for the mouse. Ker-Snapo! A centimeter long arc jumped from my hand to the longitudinal seam in the mouse. This was followed immediately by the GREEN screen, so I knew I had big trouble on the docket (failure to gain memory access). Disassembly of the mouse revealed that there is a connector header with the crimp ends of eight mouse wires within a few millimeters of the tongue and groove casing fit. It must take about ten thousand volts to get to it, but I had taken on easily twice that (somehow) in the lunge. Wondering what might have failed, I grabbed my A1000 schematic set and began looking for what might have taken it tough. As in your case, I was astonished to see the P0X, P0Y, P1X, and P1Y lines going directly to the 8364 MSI chip (Paula) without a buffer IC in between. There was a 220 ohm resistor in series with each line, and there was a 0.047 uF bypass capacitor at the MSI chip pin. Since Paula is directly addressed on the blitter bus, I felt certain that I had a dead Paula chip. I have two Amiga 1000 machines, so I was well prepared to find out what had died. Realizing that I may very well have a propagative failure [a propagative failure is a failure in one or more parts that results in destruction of the swap test object immediately upon power-up; propagative failures can ruin every test part you swap while trying to determine a single-point failure], I nonetheless began to swap stuff from one computer to the other. A reboot not only did not show a green screen, the LED didn't flash. Changing Paula had no effect. I finally had the machine stripped down to almost nothing with still no result when I decided maybe it was better to plug the parts one at a time into the working machine rather than vice-versa. You'd be amazed at how few parts need to be in the Amiga 1000 and still allow it to boot to the point that it can yet send the boot audio to the monitor. In my case, the Michigan Insider was gone, and I had removed the internal disk drive and the Paula chip. It would not boot without the A1000 daughter board, though. The dead chip turned out to be one of the [infamous] 8520 pair. The 8520 wiring goes nowhere near the mouse port, according to my schematic set. I did have a Canon PJ1080A printer plugged into the parallel port, but all of the peripherals were plugged into the same AC common strip. The modem is isolated (except for stray capacitance). It was the parallel port 8520 that got nailed. I am thus disposed to the notion that the 0.047 uF bypass capacitors that protect Paula had in fact been instrumental in the destruction of the 8520 (U6P). The 8520 must have a weak substrate diode protect structure to be vulnerable to this kind of incident (elevation of the common potential above that of the I/O pins). Paula, the mouse, and the sixteen cent SN74LS157 mouse mux chip survived ok. What to do? Well, don't grab your mouse when you're running around the house with an extra Coulomb or two of miscellaneous kitty-cat ions. What I did was bend one end of a paper clip to just the right length and stick it in the little hole along side the forth pin up from the tail of the mouse (the black wire - it's connected to the shield part of the mouse plug), arranging the clip so that it lies parallel to the cover seam. That way, the next time I arc it, it will dump to the Amiga RFI shield, and the ground elevation will be confined to the mouse proper. That's not to say it will avoid all damage. It's just that the damage will be likely restricted to the mouse. As soon as I get some new 8520 chips, I'll test this... (Gutsy-est move I ever saw, man...) Until I have a chance to test it, note this DISCLAIMER: What you do to your mouse is your own business, and none of mine. This is just my best guess of what to do to get an edge up on the situation. If you try this on your Amiga and get unsatisfactory results, I am here and now disclaiming any and every responsibility for whatever happens that displeases you. In the mean time, I advise CBM to DO SOMETHING about this - please get the mouse some underware. Howard Hull hull@hao.ucar.edu
bryce@cbmvax.UUCP (Bryce Nesbitt) (02/28/89)
In article <1485@ncar.ucar.edu> hull@hao.UCAR.EDU (Howard Hull) writes: | |The dead chip turned out to be one of the [infamous] 8520 pair. The 8520 |wiring goes nowhere near the mouse port, according to my schematic set. Wrong. The left mouse button goes directly to an 8520 IO pin. | hull@hao.ucar.edu -- |\_/| . ACK!, NAK!, EOT!, SOH! {O o} . Bryce Nesbitt (") BIX: bnesbitt U USENET: cbmvax!bryce@uunet.uu.NET -or- rutgers!cbmvax!bryce Lawyers: America's untapped export market.
mclek@dcatla.UUCP (Larry E. Kollar) (03/01/89)
When I moved my 500 into a new, carpeted room, I found a can of anti-static spray and wetted down the surrounding carpet and my chair. I haven't noticed any static in the room (or in the rest of the house for that matter -- it's been a fairly humid winter in north Georgia). If you can't get the regular anti-static spray, mix 1/2 cup of fabric softener with a gallon of water (make a half or quarter recipe if you don't have lots of friends or carpet), put some in a spray bottle, & use that. (Fabric softeners usually have chemical to eliminate "static cling" -- it also cuts down on the finger zaps.) I wouldn't recommend spraying the computer directly. :-) It wouldn't hurt to take other, previously-mentioned, precautions as well. (And don't blame me if this doesn't work -- I'm not making money off it....) My wife used it in the office where she used to work, and never had any static-related computer problems. -- Larry Kollar ...!gatech!dcatla!mclek The more I use MultiFinder, the more I like my Amiga.
ejkst@cisunx.UUCP (Eric J. Kennedy) (03/01/89)
In article <1485@ncar.ucar.edu> hull@hao.UCAR.EDU (Howard Hull) writes:
<I just the other day frazzed an Amiga 1000. Here in Colorado, static
<electricity generation is an extreme winter hazard. I am always very
<careful about static electricity, having developed a number of "peculiar"
<habits, such as touching another person in some unrestricted part of
<their anatomy or touching a light switchplate or a lamp, or the finger
<stop on my dial telephone before handing them any electronic parts or
<circuit boards, even those in protective packaging. I never reach for
<the keyboard on approaching the Amiga without touching the desk lamp
<first. At work we use static mats on the floor and benches to provide
<grounding and to suppress generation of static charge. A wrist strap
All good points. Another tip that I greeted with scorn until I tried it
is to prepare a solution of about 20% liquid fabric softener in water in
a spray bottle. Spray the solution librally around the carpet near the
computer and let it dry for 10 minutes or so. It really works.
--
Eric Kennedy
ejkst@cisunx.UUCP