11/34 sanity check

Josh Dersch derschjo at gmail.com
Sat Apr 25 11:30:51 CDT 2015

> On Apr 25, 2015, at 4:58 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:
>> From: Josh Dersch 
>> the power supply was completely dead. I've rebuilt the supply
> Just out of curiousity, what was the failure mode? (Also, trying to figure
> out of the failure could have killed things…)

After replacing the capacitors, everything was working except the H745 (-5, +20V) which immediately smoked a resistor in a very spectacular fashion (flames).  This was due to a shorted output transistor, and now things are OK.

> BTW, is it in a BA11-K box, or a BA11-L?

It’s in a BA11-K.

>> the AC LO and DC LO signals are high (these are active low, right?)
> Yes. All UNIBUS signals are active low _except_ for grants, if memory
> serves...
>> The status register display is dark.
> Hmmm.
>> The system does not respond to any keypresses on the panel.
> Sounds like you've got the variant with the real ("Programmer's") front panel
> - that's a plus. Although it's too bad that variant doesn't have a
> "HALT/CONTINUE" switch - it would have been good to power it on with the HALT
> on, which would have prevented it from trying to do any bus cycles.

Yeah, I have the programmer’s panel (yay!).  

> No response to HALT/CRTL, though? Although I'm not sure if it would respond
> to that if it was in a double-bus fault loop (NXM on trying to respond to a
> NXM).

No response at all to HALT/CTRL (or anything else).  I kind of expected that I’d at least be able to halt the processor and punch in numbers even if the CPU faulted, but I’ve never dealt with an 11/34 before.  The run light is on, the other lights are all halfway-lit (dim).  If I pull the bootstrap terminator and the unibus terminator at the other and and fire it up, the run light is on but the other lights are completely off (and the panel is still unresponsive).

>> I've taken it down to a pretty minimal configuration, sans any memory
>> or other stuff.
> Always wise... :-)
>> Slot 3: (AB) M9301 (bootstrap terminator) / (CDEF) M7859 (front panel board)
> Most 11/34's run those cards in slot 4, not 3 (probably to leave room for the
> FPP/Cache in slot 3), but slots 3 and 3 are (AFAIK) identical, so it should
> be OK to run them there.
>> the NPG jumpers on CB1-CB2 are all present on the backplane. 
> Err, I hope that's a typo for "CA1-CB1" - tying CB1 to CB2 (+15V) would not
> be good (although if you did do it, it should be harmless in this
> configuration).

Er, yeah.  Sorry, it was late when I wrote that :).

> I don't really have much to add to Don's message, about the next things to
> try. There doesn't seem to be a way to configure the M9301 to have the
> machine halt on power up, which would to my mind be the ideal. It might be
> worth throwing a 'scope probe on MSYN, to see if it's trying to do bus cycles.

The machine came with an SLU and an 128KW memory board and with those installed (SLU in slot 4, memory in slot 5, which is precisely how it was configured when I got the machine) I get exactly the same behavior.  Just in case I hooked up the SLU to a terminal and I get nothing there either…

Thanks (and thanks to Don as well) for the tips…

- Josh

> 	Noel

More information about the cctalk mailing list