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computers / comp.sys.apple2 / Re: Apple IIe troubleshooting

SubjectAuthor
o Re: Apple IIe troubleshootingDean Claxton

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Re: Apple IIe troubleshooting

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Date: Thu, 12 Jan 2023 16:34:59 -0800 (PST)
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Subject: Re: Apple IIe troubleshooting
From: deanclax...@gmail.com (Dean Claxton)
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 by: Dean Claxton - Fri, 13 Jan 2023 00:34 UTC

On Wednesday, 14 May 2014 at 04:45:41 UTC+10, Michael J. Mahon wrote:
> retrogear <larry...@gmail.com> wrote:
> >> *C600
> >> returns
> >> C600-A2
> >
> > A2 is the first byte of the slot 6 disk card. That indicates it is reading the
> > rom address and data. I meant to type *C600L to get a listing of the rom
> > something like this:
> >
> > C600 A2 20 LDX #$20
> > C602 A0 00 LDY #$00
> > C604 A2 03 LDX #$03
> > C606 86 3C STX $3C
> > C608 8A TXA
> > C609 0A ASL A
> > C60A 24 3C BIT $3C
> > C60C F0 10 BEQ $C61E
> > C60E 05 3C ORA $3C
> >
> > (and so on)
> >
> > if it's reading the ROM like this then try:
> >
> > *C600G
> >
> > to execute the boot floppy code with the disk drive connected.
> > The motor should come on and the drive recalibrate. If no drive activity,
> > and the card and drive are ok and connected correctly then I would think
> > more like a power supply problem feeding the card to power the motor, etc. There are
> > +5 -5 +12 -12 supply lines feeding and if one is bad then I would think
> > you could have a condition as you describe. Let me end this by saying I
> > do not have experience troubleshooting Apple II computers in particular
> > but many years of troubleshooting electronics and pc's in general. So my
> > advice is worth about
> > two cents :)
> >
> > Larry
> Or /DEVSEL could be missing, or...
>
> If the rest of the machine works, including video, then power is almost
> certainly reaching the slots.
>
> If power is not making it from the slot to the drive, there are connections
> on the card, a cable and two connectors, and the drive's select logic that
> could be an issue.
>
> Under the rash assumption that no card, cable, or drive is killing other
> things, it is *extremely* helpful to isolate which subassembly is failing..
> This is easily done by swapping one element at a time in a working system:
> processor, disk controller, cable, and drive.
>
> When you discover which subassembly "moves the fault", then you have (very
> likely) discovered which subassembly contains the fault.
>
> If it's still the processor, then fault isolation can move to the next
> level--inside the processor.
>
> If you can list the contents of the disk controller's ROM, then the address
> and data lines are working and /IOSELECT for the slot is working.
> Of course, +5v is also working.
>
> You can reference the MOTORON and MOTOROFF soft switches directly for the
> controller slot using the monitor. If they don't start and stop the motor,
> then any subassembly (above) could be bad. Isolating the failing
> subassembly is critical.
> --
> -michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon

I'm not sure whether the original issue was resolved, but I had a similar issue myself. The unit (platinum //e) would turn on and boot straight to a prompt rather than trying to boot from floppy. I tested the various select signals with a logic probe (IO select, device select, io strobe) and that all looked ok. On inspecting slot memory (C600L for example) however, I was frequently seeing incorrect bits in the upper nibble. This pointed to the 74LS245 bus transceiver being flaky as the data bus to the CPU was all good - just slot data was affected. Replacing the 74LS245 resolved the problem.

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