5 Aug
2011
5 Aug
'11
10:37 a.m.
On Thu, 4 Aug 2011 19:37:35 +0100 (BST)
ard at p850ug1.demon.co.uk (Tony Duell) wrote:
My point (and I am being pedantic I suppose) is that this is not an SPC
slot. It's a special slot for the console controller.
Eh? The SPC signasl are a rearrangement of the
Unibus signals
I know.
The HALT signal is not, AFAIK, a Unibus signal at
all.
And this is the problem. These signals are available in a SPC slot and used by the console but not covered by the Unibus
documentation. I
still have to google for a description of those signals.
Good luck!. There may be something in an 11/34 techncial manaul, but much
of the time on thigns like this I find I have to work them out from the
schemcatics.
Incidentalluy lookign at Unius cycles with a
logic analyser is quite
easy. I normally trigger on the falling edge of MSYN, qalified by the
address lines. You need a lot og LA channels to be useful, though.
I have 40
channels at 50 MHz or 16 at 300 MHz. That should be enough for some basic testing. A friend gave me an isolating
transformer. So I
can exclude ground loop problems. He will give me a logic probe also
next week. This seems to be a simple but helpfull and effective test
tool.
A logic probe is very useful,but bve warned it doesn't give the full
story. The prove will tell you if a clock is running, or if a data line
is stuck high or low, but if it shows a signal as changing, it tells you
nothing abotu the timing of that signal. That;s what you use the 'scope
of logic analyser for (and yes, I have been cuaght by this...)
My favourite tool for going over a machine looking for silly faults is a
LogicDart, which combines a logic rpboe with a simple3-channel logic
analyser. Problem it,s it's not an easy thing to find (and AFAIK there's
no modern replacemetn that does quite the same thing).
I checked the +5 V supply again using the isolating transformer.
Voltages look much cleaner now. But I get a dampened oszilation with
ca. 0.5 Vpp. This occures at about 17.8 kHz. Seems to be "ring" from
the SMPSU as I have only a very low load
That sounds like noise at the switching frequency. My guess is that it
means the output capacitor (IIRC the second-largest one in the module)
oin the 5V regualor brick is developing a high ESR. Probably worth
testing/replacing it.
-tony