Resolved: Re: 11/34 sanity check

Josh Dersch derschjo at
Sun Apr 26 19:45:36 CDT 2015

On 4/26/15 4:42 PM, js at wrote:
> Choosing to take your words literally...
> "Yes, I can see how this issue would be in precisely the same class as 
> not having the computer plugged into the wall."
> *** To correct you, your issue wasn't "precisely" in the same class as 
> a line cord, nor is that what I wrote or even implied... but having 
> several 11/34 myself, and having initially run into the same cable 
> reversal issue (but now, over a year later, not remembering any 
> details), the very fact that there's no keys or any clear indications 
> whatsoever which way the cable goes, made cable orientation the number 
> one suspect... and to me, an *obvious* thing to try first.
To be 100% clear -- the ribbon cable on my /34 has a clearly marked red 
stripe on it indicating pin 1 (or so I thought), and the BERG connector 
at the end of the cable has an arrow embossed on it, coinciding with the 
red stripe.  On the KY-11 UNIBUS card there is a male BERG connector 
with the same arrow marking (and IIRC, the solder mask has an "A" near 
that as well).  This also matches up nicely with the diagrams in the 
service manual.  So there were some pretty clear indications of cable 
orientation. I had never disturbed the connection at the other end (on 
the front panel) when going over the machine so never considered that 
the markings might have been misleading.  I did double (and triple) 
check the orientation of the cable on the card end before I sent my 
mail, but it never occurred to me to just try flipping it around since 
usually that's a pretty good way to let the magic smoke out of things.

I'll admit that I probably should have double checked the connection on 
the console end, but if you'll allow me, I'll chalk that up to a simple 
oversight rather than being lazy.

> However, I *do* admit to implying in my response that I'm of the 
> opinion that *sometimes* people come running to the list here the 
> instant any slight snag is encountered, without really exercising due 
> diligence, when they might take on the challenge a bit more before 
> doing so, thus have all the more satisfaction from arriving at the 
> solution.
Go back and read my initial mail.  I thought I made it clear that (A) 
I'm pretty green at UNIBUS PDP-11 stuff and that (B) what I was looking 
for was a sanity check -- that I hadn't overlooked anything glaringly 
obvious before I started really digging in with the logic probe.  I was 
not looking for someone to debug the issue for me, I just wanted to make 
sure that my configuration was at least theoretically correct by 
bouncing it off people with more experience before I spent a day 
debugging and finding out it was a misplaced card all along.

Later the focus turned to the front panel itself and I was preparing for 
a long debugging session with it when a listmember suggested not 
trusting the cable markings.

- Josh

> "A thousand apologies for wasting so much of your time. "
> Oh, only a small (1) was needed, but thank you.  :)
> - J.
> On 4/26/2015 4:49 PM, Josh Dersch wrote:
>> Yes, I can see how this issue would be in precisely the same class as 
>> not having the computer plugged into the wall.
>> A thousand apologies for wasting so much of your time.
>> - Josh
>>> J, to save the time of those posting,
>>> it's more or less assumed you've already
>>> tried the obvious things before asking
>>> for help.    Otherwise, posters are --
>>> for example -- left having to first
>>> question whether a machine is even
>>> plugged in to the wall or not.
>>> - J

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