27 Apr
2010
27 Apr
'10
4:08 a.m.
On Mon, 26 Apr 2010, Tony Duell wrote:
I believe that's fine. By my reading, the drive would not come ready if
there were a servo lock problem.
On Sat, 24 Apr 2010, Tony Duell wrote:
Well, it _may_ be... I've had another look at the manual on Bitsavers.
There's a clock track on the bottom platter with a fixed head (as you
say). This seems ot be used as the feedback of the motor speed control,
it also can be divided down to produce the sector pulse or a bit clock.
Of course the controller doesn't have to use that signal.
Unfortuately much of this circuitry seems to be in one of the gate
arrays. This will make it difficult to debug and even more diffuclt to
repair. I hope that's not the problem.
But I woul still check it. See if tyhe motor speed feedback signal looks
sensible too while you're in there.. Is this a hard sectored dirve? In any case does
the cotnroller use the
index pulse fro anyhting? Is that presnet and correct?
Sorry, didn't answer this part of your post: From my read of the
technical manual, it is hard sectored. There's a dedicated index track on And also, of course ,look at the read data signal.
Does it look senesible?
I've poked around a bit with a scope. The base clock signals mentioned in
the troubleshooting section of the manual are present, shaped correctly,
but the periodicity is exactly 2x what's printed there. This is a tough
call, though. The manual is for a different (and I believe later) drive
model, so that difference might be as expected. It's also possible that
it's a typo. If the period was too small, I'd suspect a bad latch in the
clock divider. But, _slower_? It's hard to see what type of failure mode
would cause that, but perhaps I'm missing the obvious.
The index and sector pulses appear to be right on the money.
If I look at the output of the analog section, I can see what looks to be
reasonable read data. Unfortunately, from this point on there are
significant differences between the bitsavers doc and this drive. The
board layout is very different on mine and it has fewer gate array chips.
The manual suggests that the clock separator PLL is in the gate array,
while mine has a DIP MC4044 PLL serving that function. I admit to being a
bit fuzzy on how this stage operates (not an EE by background).
Could this be a controller problem? Do you know
whether either the
controller of drive are definitely OK?
I have no assurance that either is functional. They were in storage for
25 years and the previous owner isn't clear on whether the drive was
functional (he bought the system from the original purchaser and did not
use it).
Steve
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