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

Robert Jarratt robert.jarratt at
Fri Feb 6 12:39:55 CST 2015

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Noel
> Chiappa
> Sent: 06 February 2015 00:17
> To: cctalk at
> Cc: jnc at
> Subject: Re: It's time to restore the 11/45 - progress!
>     > 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
>     > 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
> but if you understand a lot of what's going on, I'm sure someone here can
> 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
> 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
> universal solvent), a capacitance meter, etc, etc. (Also an ohmmeter, to
> 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_
> need a decent 'scope. Don't even _try_ thinking you can do it without one.
> Fuhgeddaboutit.
> 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
> (We did.)
> Past that? Well, there are things that are nice to have (e.g. a
> station), but you can often work around them (e.g. a pair of dikes and a
> sucker).

I am sooo happy that I finally bought a desoldering station. Not an
expensive one, but it really does make life easier.

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

I am starting to feel the need for one of these. I bought a cheap Thurlby
one a few months ago, but the membrane keyboard doesn't work, even though
the rest of it seems fine :( My backup plan is to use a Spartan 3 dev board
as a self-made logic analyser. I will connect it to the pods I got with the


> 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
> mind immediately - perhaps someone else here can add to the list.
> 	Noel

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