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   Newsgroups: comp.sys.apple2   
   Date: Thu, 12 Jan 2023 16:34:59 -0800 (PST)   
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   Subject: Re: Apple IIe troubleshooting   
   From: Dean Claxton    
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   From: deanclaxton@gmail.com   
      
   On Wednesday, 14 May 2014 at 04:45:41 UTC+10, Michael J. Mahon wrote:   
   > retrogear  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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