Troubleshooting a N* Advantage

[Steven Hirsch]

On Sat, 6 Jun 2015, Steven Hirsch wrote:

> My Advantage decided to stop booting from floppy disks (the only media it is 
> capable of booting).  At first it threw random disk errors, then progressed 
> to the point where I get an immediate "Hardware Failure" diagnostic on screen 
> at power up.  If I reset and hit 'Enter' it starts the disk drive comes right 
> back with a "?" prompt and LOAD SYSTEM.

Spent some further time with the unit.  I had a hunch that the "Hardware 
Failure" diagnostic might be a memory parity error (the Advantage is one 
of the few machines I've seen of this vintage that has a parity chip on 
each bank).  Starting swapping in some extra 4116s and finally brought it 
to the point where CP/M signs on, the drive steps to the directory track 
and dies with a an error code:

T 1 D 1 S 0010

According to the documentation:

T1 = Sync byte not found
D1 = Drive A
S 0010 = Sector 10 (decimal)

It's almost certainly not bad media. I tried several different (and 
previously working) bootable diskettes with exactly the same results. 
When I try to boot the GDOS demo diskette, it clears the screen, starts 
making a repetitive "buzz" from the speaker and hangs.

Is anyone familiar enough with the circuit to suggest a starting point for 
further troubleshooting?


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