Vector Graphic Seagate ST-506 5MB Hard Drive "The
ST-506 was the first 5.25 inch hard disk drive."
ST-506 from Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/ST-506
Subject: ST506/ST412 hard drivesFrom: Dennis Ray WingoDate: Mon, 31 Dec 2007
The standard ST-506 drive's index signal is not sent across the interface until the drive is selected. It takes a little while (onthe order of a half second) for the CMOS 4040 PLL (Pin 1 on the chip)to "sync up. The chip is actually a phase comparator that compares a reference signal to the index and the pin 1 is an error signal thatis used as a feedback to the sync circuit.
What you have to do is do a trace cut and jumper on the drive so that the index
signal is always present on the interface. Piece of cake!
You have to get an ST-506 control card diagram to figure out where to
do the cut & jumper. Otherwise the FD/HD does not sync up and you
get an error signal on disk read and the Vector OS does not do enough
retries to get around the issue.
Dennis
Warning: The following modification has not been verified. The instructions
may contain errors or may not apply to all versions of the ST-506 board.
Notes from meeting with Dennis Wingo, while working ant Vector Graphic
Warning: The note jumper 4-5 may be incorrect and should be 2-5. The
chip 7438N is on Control Assy 20040 andControl Assy 20040 EC0138,
however, Control Assy 20019 Rev H has a 64S86N at this location.
Seagate ST-506 Mod for "Constant Index Pulse"
Control Assy 20040
Warning:The following modification has not been verified. The instructions
may contain errors or may not apply to all versions of the ST-506 board.
Trace P20 on the small connector
Find the output pin
Find the input pin
Use an Ohm Meter from one input pin to all other input pins
Input pins will be shorted together
Select Line
Cut leg tied to other pin