[rescue] Help with Sun 3's

Mouse mouse at Rodents-Montreal.ORG
Mon Dec 24 09:26:54 CST 2018

> Recently acquired a few sun 3's [...].

> I've tried both with a monitor and with a serial terminal using a 25
> pin to 9 pin null modem cable and then a 9 to 25 adapter so I had 25
> on both ends.
> [...]
> But no output to either the monitor or the serial terminal.

> Any ideas what could be wrong here?

I'm going to write assuming you know little-to-nothing about
electronics.  If you're competent in that regard, much of what I've
written below will be unnecessary - but what you wrote didn't give me
any idea how much you know about electronics, so I'd rather give
unnecessary information than leave bits out.

The most likely thing, I'd guess, is that your serial-line wiring needs
to have transmit and receive swapped.  Depending on whether the 9/25
adapters you're using (one with a cable, one without) were designed for
DTE or DCE, they may wire those pins differently.

Personally, I'd just grab a serial cable from my box-of-cables and, if
it didn't work, add a null-modem thingy on one end.  If you don't have
such things on hand...well, it depends on what you _do_ have on hand.
I'll assume you don't, since if you did I'd've expected you to try
adding one (and mention it in your post).

First, I'd check that this is, or at least could be, the problem.  Grab
two LEDs and a 100 ohm resistor and connect them up (with solder,
alligator clip leads, or even just twisted bits of wire) with the LEDs
in parallel but with reversed polarity and the resistor in series with
the result (see below).  Then, unplug your serial cabling from one
device (doesn't matter which one), but leave both devices powered up.
On the device, connect one end of the LEDs-and-resistor (doesn't matter
which one) to pin 7 if it's a DB-25s or pin 5 if it's a DE-9 and then
probe pins 2 and 3 (same pin numbers on either sort of connector) with
the other end.  On one of the pins, one LED should light; on the other,
both should stay dark.  The one that lights a LED is the transmit pin
for that device.  Do the same with the now-disconnected cable end.

If they're both using the same pin for transmit (eg, device pin 2
lights up and so does cable pin 2), this is your problem - or, at
least, it's _a_ problem, one that needs to be fixed before you can get
anywhere with serial console; there may be other problems.  (Video
console won't work without a keyboard plugged in (or, in some cases,
some unusual firmware settings), and you didn't mention any keyboards.)

Don't worry about shorting things to one another.  Serial ports are
incredibly forgiving of such things; the spec says that the driving
electronics must be such that any pins or combination of pins may be
shorted together and/or to any voltage source(s) within range (which
means about 25 volts either way from ground) indefinitely without
damage.  You also have no need to worry about shocking yourself, at
least not unless your hands are wet with salty water or you're bleeding
all over the wires or some such (and quite possibly even then).

In case my description of the LEDs-and-resistor circuit above wasn't
clear enough, here's a sketch (which I hope your UA renders with a
fixed-width font, or it'll look awful and probably unreadable):

             |   LED 1   |    100 ohm
one end -----+           +----/\/\/\/---- other end
             |   LED 2   |

If you don't have even LEDs and resistors on hand, I'm not sure what to
suggest.  If your terminal uses a DB25F (instead of DB25M), and you
have some highish-gauge wire (AWG somewhere in the 20-30 range - small
enough to fit in the holes in the connectors), you can just wire 7 to
7, 2 to 2, 3 to 3, and if it doesn't work then try swapping 2 and 3.

If that's not it...well, I haven't seen a Sun-3/60 that works but won't
drive _something_ out the serial port on power-up with no keyboard.
You can also try port B, which...I can't recall.  Either it's a
separate connector or it's on the same connector but uses pins 14 and
16 instead of pins 2 and 3; I don't recall which way the -3/60 did it.
If you have the single-connector sort, there exist breakout cables,
though they are comparatively rare; I've got only about two that I
didn't solder up myself.  If need be you can stick bits of wire into
the holes on the connector; I've done that often enough.

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