On 2014-12-15 18:06, John Rollins wrote:
So in function checking the PDP-11 now that the
Series/1 is out of the basement and I have room to move the unit around and plug it in, I
have discovered that it doesn't appear to transmit data from the console port on the
back. I have tried two terminals(WY99) and two different PC's(Windows laptop with
hardware serial port and a Mac with a USB adapter) with various software, a half dozen
different cables, and every conceivable switch setting on the PDP with nothing to show for
it aside from a lot of time spent the last couple of weekends.
So when I power up, the LED display on the front counts down through the numbers and
stops at 4. As near as I can tell, this is something of a good sign. But nothing ever
comes up on a connected terminal. Sometimes pressing keys on the terminal results in the
RUN light turning off, other times it does nothing. This would seem to indicate that the
PDP knows that something is trying to talk to it, but it is not sending data out.
Short of spending an entire day disassembling half the machine and tracing every wire
hoping to find something out of place, does anyone have any ideas on what may be happening
here, or what to look for?
Well. The first to check is if you have expected levels on the pins of
the serial port. At idle it should hover at about -12V, although the
RS-232 spec allows for significant variation. But it should be an
obvious negative value anyway.
Also check that your terminal also asserts such a value. And that if the
terminal does it on pin 2, then the PDP-11 should do it on pin 3.
(Obivously.)
What I am thinking is that the level converters might be blown. Not
uncommon in older systems. If so, that is all you need to replace. It's
normally a single chip.
This also makes sure you are not using broken or wrong cables. (Oh yeah,
and ground is on pin 7.)
If this don't help, then we need to dig further...
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol