On 2023-Jul-05, at 9:45 AM, <[email protected]>
<[email protected]> 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.
