``IOM'' is just a ``wrapper'' name to the combination of an IOB with its power cable.
The I/O board reroutes both the control signals of the existing Mark~III controller board and the actual data signals for WRM~1 and 3. It also recovers the clock present in those two signals that are going to the decoder by using AT&T clock synchronizer chips.
An assembled IOB is shown in figure iob.eps .
This is a standard double-sided PCB with plated-through holes and 35~μm of copper. A copy of the original Haystack documentation of IOB can be found in the directory ftp://kurp-ftp.hut.fi/pub/mk4/iom/io-board and printouts of these files are provided in the section ``IOM'' of the documentation binder.
(The original files are located at ftp://card.haystack.edu/pub/mark4/4712/io-board .)
Instead of the standard board documentation files discussed in Standard Files , the following files are provided:
pub/mk4/iom/io-board/docmit.drl
pub/mk4/iom/io-board/mit.top
pub/mk4/iom/io-board/mit.bot
pub/mk4/iom/io-board/mit.slk
pub/mk4/iom/io-board/mit.smk
pub/mk4/iom/io-board/mit.ncd
pub/mk4/iom/io-board/mit.rep
pub/mk4/iom/io-board/DisketteLabel
The original Haystack PCB layout fails to connect write voltage disable lines according to the schematic. Thus, two corrections must be made:
P1-5 -- wire -- J1-35 (DISABLE1 -- /REC01)
P1-6 -- wire -- J2-35 (DISABLE2 -- /REC02)
This cable supplies power to the IOB and also transmits the write voltage disable signals from IOB to PWM for further redistribution to WRMs. (WRM~1 and 3 receive DISABLE1 and WRM~2 and 4 receive DISABLE2.) See Haystack drawing 4712A106 for a reference description of this cable. Cut about 160cm/64 inches 6-way 20AWG Alpha cable type ``1896/6C''. Crimp small AMP pin contacts 66506-9 at PWM end and put them into an AMP 206434-1 plug with a cable clamp 206062-1 in the following order:
Red -- J6-1 (+5V)
Blue -- J6-2 (RETURN)
Green -- J6-3 (-5V)
Black -- J6-4 (-5V RETURN)
White -- J6-5 (DISABLE1)
Orange -- J6-6 (DISABLE2)
Strip the outer sheath of cable at IOB end for about 50mm. Use 70mm clear heat shrink tubing and let about 10mm of tubing extend over stripped wires. Cut wires 30mm after the end of heat shrink tubing and push them into an AMP 640426-6 Matenlok connector using AMP hand tool 59804-1 in the following order:
Red -- P1-1 (+5V)
Blue -- P1-2 (RETURN)
Green -- P1-3 (-5V)
Black -- P1-4 (-5V RETURN)
White -- P1-5 (DISABLE1)
Orange -- P1-6 (DISABLE2)
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