Vector and ST506 (was ST506 and-or ST412 hard drives

[dwight elvey]

> From: lynchaj at yahoo.com
>
---snip---
>
> Hi Chuck,
>
> Yes you are correct. I spoke with the VG engineer to get more details on
> "constant index" and you described it exactly.
>
> Apparently there is a cut and jumper modification which can be made to the
> ST506 circuit board to bring the /INDEX signal to the interface constantly
> even when the drive is not selected.
>
> Once I get a ST506 drive I will find and make the modification. Assuming I
> can get the ST506 to work, I will try making modifications to ST225's or
> other more common hard drives.
>
> I'd like to get the standard case working to establish if my VEDMCS is
> working properly before adding in other variables of different drives etc.
>
>

Hi Andrew
 When you find your drive, it should be easy to make the mod.
Follow the signal back from the pin. There should be a line
driver there. Usually something like a 74S38 or a 7545x.
These usually have two inputs. Using a scope or a logic probe,
you'll see one input with the index and the other will be
static. The static one is the one to tie high to get a constant
Index. The easiest way is to cut the IC lead near the board
and lift it away a little. You can then put a pullup resistor
on this lead.

 I like doing this more than cutting the circuit board.
If restoring, one can replace the IC or just bend the lead back
solder it back.
Dwight

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