[sebhc] Z-37 Diag Disk

Lee Hart leeahart at earthlink.net
Wed Mar 23 00:42:42 CST 2005

Dan Lanciani wrote:
> |> Does the disk so created read ok on another system?
> |No, it does not.
> That would argue against a problem with the "data separator"
> (really clock recovery) circuit.

Yes. Though I think it means the one-shots may need adjusting (it uses
trimpots for the write precompensation and pulse width shaping). I've
taken the write problem to mean that there is more than one thing wrong.
But write is easier to deal with than read.

> What about the master clock itself?

It's a 16 mHz crystal oscillator and divider. It seems to be at the
right frequency working correctly.

> Were you able to check or swap it?

In fact, one of the things I want to do is unsolder it from the bad
board and try it on my otherwise known good board. I haven't done that
yet. It might be that its frequency is *slightly* off that I can't tell
with my scope, but it's enough to cause read/write problems. It is
probably significant that Heath did not use the 2.048 MHz bus clock;
they instead used a crystal oscillator to get exactly 2.000 MHz.

> Am I remembering correctly that the H89 version was similar except
> that it did not need the HLT/NOP hack for synchronization?

I haven't compared the two schematics to see.

> Did you try single as well as double density?

No. That could be another thing to try.
"Never doubt that the work of a small group of thoughtful, committed
citizens can change the world. Indeed, it's the only thing that ever
has!" -- Margaret Mead
Lee A. Hart  814 8th Ave N  Sartell MN 56377  leeahart_at_earthlink.net

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