It's time to restore the 11/45 - progress!

Noel Chiappa jnc at
Thu Feb 5 18:16:53 CST 2015

    > From: Jacob Ritorto

    > I guess this crowbar thing tripping, is just its way of trying to
    > protect the rest of the system from overcurrent, right?

Over-voltage. Voltage != current. :-)

    > And the dried up cap is one thing what could make it think there was an
    > overcurrent situation, correct?

I think the concept is that the cap could have shorted out, thereby causing a
too-high voltage to pass through it - or something like that! :-) In general,
cause the circuit to mis-behave.

    > I don't know that I'm going to understand how to read the schematic.
I struggle with the analog circuits too. Just keep plugging away at it, each
will slowly start to make sense. (Not the most complicated/sophisticated
aspects, but if you understand a lot of what's going on, I'm sure someone
here can help on the tricky bits.)

    > Also going to try to find a manual that describes the power supply.

DEC's maintainence/technical manuals are very good indeed for explaining how
the analog circuits work - especially for those of us who can't just glance at
a schematic and instantly, intuitively understand how the whole thing
works. For me, reading them is really pretty much a must before trying to
debug/repair analog stuff.

    > But what is a valid test once I find it?

This is where you need test instruments; an ESR meter (although that's not a
universal solvent), a capacitance meter, etc, etc. (Also an ohmmeter, to
check for shorted caps.)

    > I don't have much electronics gear here.

If you seriously expect to repair something like an 11/45, at a _minimum_ you
need a decent 'scope. Don't even _try_ thinking you can do it without one.

I like Tektronix 465's - they are common on eBay, and if you're patient, you
can get one for $60-70. They are also a 'scope much used on these machines
BITD. (We did.)

Past that? Well, there are things that are nice to have (e.g. a de-soldering
station), but you can often work around them (e.g. a pair of dikes and a
solder sucker). A logic analyser would be nice, and I keep meaning to get one,
but I haven't, yet, so they aren't essential. (Although for _some_ faults, a
'scope just doesn't cut it. If you can write a loop, fine. If not... time for
a logic analyzer.)

I'm trying to think what else is absolutely essential, past the 'scope (and
the meter - you ought to buy your own, they aren't that much). Nothing comes
to mind immediately - perhaps someone else here can add to the list.


More information about the cctech mailing list