5 Jul
2023
5 Jul
'23
3:08 p.m.
On 2023-Jul-05, at 9:45 AM, <brad(a)techtimetraveller.com>
<brad(a)techtimetraveller.com> wrote:
Thank you! I couldn't remember if I'd posted
it here before, I've been off
the list for a while.
Because I don't know really anything about it, I'd been operating on the
belief the power sent from the PSU was DC. So maybe that's my issue. There
is a single 10 pin connector from the PSU to the motherboard. I tested for
DC and found the following:
Brown - +5V
Red - +5V
Orange - +5V
Yellow - -16V
Green - +16V
Blue - -0.8V
Purple - GND
Grey - GND
White - GND
Black - -2.4V
I'm not sure if the +16 and -16v need to be adjusted, or if they are that
high because they don't have a load during my testing. The -16V is directly
connected to the VEE on a nearby 1488, and I think the max voltage there
should be -15V.
The blue and black are the ones that didn't seem right. But, if they're not
DC then maybe that's my issue. Also last night I found more cold solder
joints, so maybe one or both are affected by that. I will test with my DMM
as AC instead of DC and see if I get something there instead. Barring that,
I'm working on a schematic of the PSU to try and figure out what it's
supposed to be delivering.
Like I said, very tempting to plug in, I suspect it may be just fine.. but..
there's a lot of chips to blow up here if I'm wrong.
Seeing as how you're looking at the connections from the PS to the logic, raises the
question of how the monitor is being powered: does it have it's own PS from 120VAC,
wired to the PS directly, or from the PS via the logic board.
Some points about supplies:
- The memory chips are 1402 256*4 PMOS shift registers. These need supplies of Vcc = +5
and Vdd = -5 to -9V.
The 1402s also need higher voltage clock signals, between Vcc-15 and Vcc-17 (may be -10
to -12 relative to gnd).
The two MMH0026 ICs beside the 1402s are the clock drivers for the 1402s.
- The 3258 character generator needs -12 (and +5).
- The 1602 UART probably needs -12 (and +5).
- The RS232 needs +something and -something line-drive levels of course.
- There's what looks to be a potted crystal clock module on there, might check what
its supply is.
Could be +5, but could be something else.
- There's probably a MOS keyboard encoder that may require some supplies besides just
+5.
- Some of these supplies may be derived via components (e.g. zener & dropping R) on
the logic boards.
- And of course the monitor needs its supply(s).
Seeing as how you have some odd things appearing on the PS, if it were me, I would be:
- RE-ing the PS thoroughly,
- figuring out the power connections on the logic boards to these special ICs,
- figuring out the monitor power supply/sources
.. so it's known how all these requirements are intended to be met before powering the
whole thing up.
I recently refurbished a Teleray terminal from the same period. It uses MOS shift
registers from the same family (1404s) and similar funky clock drivers. The power supplies
design was more straightforward than what you appear to be dealing with. On things like
this I also like to look at the DB25 connector to see exactly how it's wired -
fixed-level ctl-sig outputs, connections for ctl-sig inputs that may be required, DCE vs
DTE, whether there are any non-EIA-standard connections present.