31 Jan
2008
31 Jan
'08
3:36 p.m.
Also, does anyone have a proper data sheet for the
MC3470 (disk read
amplifier etc).
A reasonable description appears in the Semens FD100 service manual.
The best analysis of a floppy read channel I have ever read appears here:
http://bitsavers.org/pdf/shugart/SA850_450_Read_Channel_Analysis_Dec79.pdf
1 Feb
1 Feb
4:05 p.m.
Also, does anyone have a proper data sheet for
the MC3470 (disk read
amplifier etc).
A reasonable description appears in the Semens FD100 service manual.
2 Feb
2 Feb
2:22 p.m.
Also, does anyone have a proper data sheet for
the MC3470 (disk read
amplifier etc).
A reasonable description appears in the Semens FD100 service manual. 
3 Feb
3 Feb
5:03 a.m.
On 02/02/2008 22:22, Tony Duell wrote:
>> > Also, does anyone have a proper data
sheet for the MC3470 (disk read
>> > amplifier etc).
However, I still have one unaswered question :
There's a DC balance
preset in the differntiator stage. What's the proceue for adjusting it?
It's to adjust the data symmetry, and for Sony and Apple drives that use
a 3470, you adjust it so that the data signal has a 50% mark/space ratio
when the input is a constant frequency (125kHz or 250kHz).
--
Pete Peter Turnbull
Network Manager
University of York
3:59 p.m.
On 02/02/2008 22:22, Tony Duell wrote:
Do you mean that? I thought the output (pin 10) pulse width was set byu
the RC network on pins 8 and 9. Do you really mean that the offset adjust
preset is used to get all the pulses equally spaced, rather than occuring
in pairs (which is the most likely result of an imbalance in the cicuit,
I think).
Or do you adjust for 50% duty cycle at some other point?
-tony
>> > Also, does anyone have a proper
data sheet for the MC3470 (disk read
>> > amplifier etc).
However, I still have one unaswered question :
There's a DC balance
preset in the differntiator stage. What's the proceue for adjusting it?
It's to adjust the data symmetry, and for Sony and Apple drives that use
a 3470, you adjust it so that the data signal has a 50% mark/space ratio
when the input is a constant frequency (125kHz or 250kHz).
5:28 p.m.
On 03/02/2008 23:59, Tony Duell wrote:
Do you mean that? I thought the output (pin 10) pulse
width was set byu
the RC network on pins 8 and 9. Do you really mean that the offset adjust
preset is used to get all the pulses equally spaced, rather than occuring
in pairs (which is the most likely result of an imbalance in the cicuit,
I think).
Or do you adjust for 50% duty cycle at some other point?
You adjust the offset adjust preset for a 50% duty cycle output,
according to the Sony manual.
--
Pete Peter Turnbull
Network Manager
University of York
4 Feb
4 Feb
2:21 p.m.
On 03/02/2008 23:59, Tony Duell wrote:
Do you mean that? I thought the output (pin 10)
pulse width was set byu
the RC network on pins 8 and 9. Do you really mean that the offset adjust
preset is used to get all the pulses equally spaced, rather than occuring
in pairs (which is the most likely result of an imbalance in the cicuit,
I think).
Or do you adjust for 50% duty cycle at some other point?
You adjust the offset adjust preset for a 50% duty cycle output,
according to the Sony manual.
--
Pete Peter Turnbull
Network Manager
University of York
2:59 p.m.
On 03/02/2008 23:59, Tony Duell wrote:
Do I conclude that you've never actually done it? Neither have I, of
course. I think I am going to have to experiment with a 'spare' drive PCB
-- I'm sure I can find a drive with ad heads or something. It'll not be
soon (too many other things to do, but I'll let you know how I get on.
-tony
Do you mean that? I thought the output (pin 10)
pulse width was set byu
the RC network on pins 8 and 9. Do you really mean that the offset adjust
preset is used to get all the pulses equally spaced, rather than occuring
in pairs (which is the most likely result of an imbalance in the cicuit,
I think).
Or do you adjust for 50% duty cycle at some other point?
You adjust the offset adjust preset for a 50% duty cycle output,
according to the Sony manual.
5:24 p.m.
On 04/02/2008 22:59, Tony Duell wrote:
Do I conclude that you've never actually done it?
Yes, I have. The last time was probably 25+ years ago, but that's
exactly what I did -- constant stream of data and set the pot for a
square wave on the scope.
--
Pete Peter Turnbull
Network Manager
University of York
3 Feb
3 Feb
1:43 p.m.
On 2 Feb 2008 at 22:22, Tony Duell wrote:
However, I still have one unaswered question :
There's a DC balance
preset in the differntiator stage. What's the proceue for adjusting it?
From the MC3470 data sheet in the 1990 Motorola Linear
and Interface
Integrated Circuits databook:
"The potentiometer across the differentiator components is adjusted
until a symmetrical digital output cycle is obtained at Pin 10 for a
sinusoidal input with the minimum anticipated Ep(omega) product."
-- Dave
6164
days inactive
6169
days old
9 comments
4 participants
participants (4)
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aek＠bitsavers.org -
ard＠p850ug1.demon.co.uk -
jdbryan＠acm.org -
pete＠dunnington.plus.com