21 Dec
2013
21 Dec
'13
4:03 p.m.
Does anyone have a source for a Fujitsu MB8866 FDC chip? I've found some
mention of it being a direct substitution for a WD1791, but the latter
does not cooperate in this machine.
Steve
--
21 Dec
21 Dec
5:56 p.m.
On 12/21/2013 01:03 PM, Steven Hirsch wrote:
Does anyone have a source for a Fujitsu MB8866 FDC
chip? I've found
some mention of it being a direct substitution for a WD1791, but the
latter does not cooperate in this machine.
Careful--the 8866 is a sub for the bare-no-suffix old WD1791; the MB8876
substitutes for the more common 1791-01 1791-02. The big difference is
in the operation of pin 33 (which shouldn't matter) and the compare
feature bits in the read and write commands, which may be what's
tripping you up.
So if you can't find an 8866, try for a no-suffix 1791.
--Chuck
22 Dec
22 Dec
2:27 p.m.
Does anyone have a source for a Fujitsu MB8866 FDC chip? I've found some
mention of it being a direct substitution for a WD1791, but the latter
does not cooperate in this machine.
I don't know if it was this one, but at least one of the Fujitsu disk
cotnrolelr ICs did not need the -12V supply whereas the
otherwise-compatible WD oen did.
It may be worth checkign you have all the necessary supplies.
-tony
3:40 p.m.
On 12/22/2013 11:27 AM, Tony Duell wrote:
I don't know if it was this one, but at least one
of the Fujitsu disk
cotnrolelr ICs did not need the -12V supply whereas the
otherwise-compatible WD oen did.
It may be worth checkign you have all the necessary supplies.
Ah, now Tony jogged my memory. Pin 40 is NC on the MB8866, whereas it's
+12 on the 1791. Perhaps just a jumper will be sufficient to remedy the
situation.
--Chuck
5:49 p.m.
On Sun, 22 Dec 2013, Chuck Guzis wrote:
On 12/22/2013 11:27 AM, Tony Duell wrote:
Thanks, all! I'm filing this information away for the next
troubleshooting adventure. The 1791 I tried as a sub was an -02 model,
which explains why it behaved so flakey.
I thought the original FDC on my Max-80 was fried, but it turned out to be
a broken lead on one of the pots in the data separator circuit. I didn't
have a 5k 10-turn trimmer in the parts bin, but I was able to grind away a
little plastic and tack a new lead on the original to get things going
again.
Steve
--
I don't know if it was this one, but at least
one of the Fujitsu disk
cotnrolelr ICs did not need the -12V supply whereas the
otherwise-compatible WD oen did.
It may be worth checkign you have all the necessary supplies.
Ah, now Tony jogged my memory. Pin 40 is NC on the MB8866, whereas it's +12
on the 1791. Perhaps just a jumper will be sufficient to remedy the
situation.
23 Dec
23 Dec
1:58 p.m.
Ah, now Tony jogged my memory. Pin 40 is NC on the
MB8866, whereas it's
+12 on the 1791. Perhaps just a jumper will be sufficient to remedy the
situation.
Yes your are right. I was confusing it with the dumb UARTs, some of which
were +5V only, otheres also needed a -12V supply.
IIRC, the Fujitsu disk cotnroller doesn't mind if you apply 12V to pin
40. So you can put the Fujitsu part in place of a WD 1791, but not
necessarily the reverse.
-tony
3940
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