PDP-11/44 problem - RUN stays on

Gooijen, Henk henk.gooijen at oce.com
Mon Nov 13 05:48:06 CST 2006

Don wrote:

> Well, that's kind of a bummer that it wasn't just a dirty contact.
> What I'd do at this point is verify all the P/S voltages are 
> within spec, and then pull all the boards that are not 
> necessary (FPU, CACHE, and any UNIBUS I/O) for basic system 
> operation. Run with just the base CPU and a memory card.
> I'd try the exam and deposit commands with the /TB (take bus) 
> option to see if you can access memory directly (you still 
> have to be able to halt the CPU).
> If the behavior is still not normal, try the CPU microstep 
> commands and see if you can step thru the microcode cycle by 
> cycle, and that the flow makes sense (the microflows are in 
> the printset).
>  From looking at the prints the RUN signal is just a FF 
> triggered by a one shot on the CPU control board. For either 
> board combo (the one that never comes out of RUN, or the one 
> that stays in RUN) I'd back track thru the logic too see if I 
> could find something wrong.
> Sorry, but I haven't had this kind of behavior in my 11/44, 
> so can't suggest a more specific place to look.
> Don

Yes, I also kind-a hoped that cleaning the fingers would correct
the problem. I actually did think of the power supply, but didn't
do any measurements for 3 reasons.
1. the BA11-A is still in the H960, only top lid is removed
2. I read about the "reputation" of the 5-fold switcher PSU ...
3. I read the documentation ...

Regarding reason #3, the System Tech manual says on page 3-10
that the CPU only needs the +5.1V power supply. I was thinking
that if I get anything on the VT100, that +5.1V must be present.
So, I did not check that! BTW, I wonder if the table 3-7 is
correct. Doesn't the CIM (M7090) need +/- 12 or 15 V. for the
RS-232 signals?  Or the MFM, I'd need to check the schematics.

I did try with FPU removed, and I did read that you can run the
11/44 without CACHE. I will try that too this evening.
And running without UBI didn't even occur to me! The memory has
dedicated slots, so it is not accessed through the UBI module?

I will try the /TB option, but I understand that if I can't halt
the CPU, the /TB option will not help much ...
Anyway, thanks for the tips, Don!
I will try the system without FPU, CACHE, UBI and just one memory
module installed. To get a running CPU that can be halted, I assume
you can even run the 11/44 without *any* memory modules?
OK, to do EXAM/DEP a memory module is useful :-)

If all this fails, I guess I will need to pull out the scope, as
I assume that microcode stepping will not work eitehr as long as
you can not halt the CPU ...
Oh well, something good has come from this. I updated the 11/44
pages on my site a little :-)

- Henk.

This message and attachment(s) are intended solely for the use of the addressee and may contain information that is privileged, confidential or otherwise exempt from disclosure under applicable law.  
If you are not the intended recipient or agent thereof responsible for delivering this message to the intended recipient, you are hereby notified that any dissemination, distribution, or copying of this communication is strictly prohibited.  
If you have received this communication in error, please notify the sender immediately by telephone and with a "reply" message.  
Thank you for your cooperation.

More information about the cctalk mailing list