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 :-)

  thanks,
- Henk.




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