Track 159 is the one of the problem tracks. Very crude analysis in Excel shows wildly varying bit cells. Very hard to say at this point if it’s the problem as I have not compared them against the rest of the disk. The problem is related to an earlier post where I mentioned “garbage” between some sectors; it’s clear I am detecting too many flux changes.
It’s like looking for a needle in a haystack. Looks like I picked the wrong week to quit sniffing glue.
My plan therefore is simple: write the dodgy track back to a disk in a effort to get a good sector from it. Then convert the sector into MFM and compare my framing with the correct waveform. It should then be very simple to find the detection error.
One thing is that if I slow down and generally mess with the disk RPM (but sticking my thumb against the flywheel) I can get what seems to be a good read – human readable text in the sectors, so that’s a good sign.
And here is the TDRead code and executable I wrote back in 1994, zipped up. If I get a moment I’ll update my contact details and release it as V1.2 to Aminet.
By the way – these 350MB captures actually compress very well as you’d expect; tried one a short time ago and got it down to around 12MB.