Bob-O-Rama
Experienced Member
Hi,
I have a AT&T 4425 Teletype Terminal I am trying to restore for daily use by some students. I am having to give up on restoring the original Astec AA12433 PSU ( -12v, +5v, +12 ). It has a TTL "DC OK" signal which goes high or low depending on all three outputs reaching the proper voltage. The new PSU does not. The terminal requires this DC OK signal to boot, and it seems to inhibit much of the internals. If I wait a second after turning on the new PSU and pull DC OK high to 5v with a pullup resistor, it boots perfectly.
I was thinking "brute force" with a set of relays ( I have some very small 12v NO relays, and the 5v pull up passed through the relays is its own "proof" of 5v being OK. ) Other suggestions or flaws with this plan welcome.
-- Bob
I have a AT&T 4425 Teletype Terminal I am trying to restore for daily use by some students. I am having to give up on restoring the original Astec AA12433 PSU ( -12v, +5v, +12 ). It has a TTL "DC OK" signal which goes high or low depending on all three outputs reaching the proper voltage. The new PSU does not. The terminal requires this DC OK signal to boot, and it seems to inhibit much of the internals. If I wait a second after turning on the new PSU and pull DC OK high to 5v with a pullup resistor, it boots perfectly.
I was thinking "brute force" with a set of relays ( I have some very small 12v NO relays, and the 5v pull up passed through the relays is its own "proof" of 5v being OK. ) Other suggestions or flaws with this plan welcome.
-- Bob