Altair

From: Dwight K. Elvey <dwightk.elvey_at_amd.com>
Date: Mon Oct 14 14:18:00 2002

>From: "Walter Peterson" <walterp_at_cyberstreet.com>
>
>The A11 light dosn't function due tyo a blown 7405 chip in the front panel. I
have had to replace several of these myself on my altair and on my IMSAI. 7406
seems to make a better replacement as it can take higher voltages
>
>
>

Hi
 I've notice these as being a common failure item, as well.
I don't think it is the voltage that is killing them. It is
more likely a timing overlap issue with other parts driving
the bus and stressing these parts. One might consider adding
some resistors in series ( small value ) to limit the current
when a tristate drive also drives the bus at the same
time as the '05 is active ( driving low ). I would suspect
that something in the order of 15 ohms would be enough
to protect the '05's and still drive a solid '0' onto the
bus lines.
 There is no reason that any voltage issue should cause
problems with these parts.
Later
Dwight
Received on Mon Oct 14 2002 - 14:18:00 BST