Re: Help restoring a 547 scope

Richard Knoppow
 

Regarding Black Beauty caps. There were several series and not all fail the way the infamous ones do with cracking and breaking cases, however, all are paper and _all_ paper caps regardless of maker have had limited lives. Anything old enough to have had BBs in it is old enough to have all its paper caps replaced regardless of make.
   I don't think polyester caps are the best choice and am not sure they are even made. Polypropylene has the best combination of characteristics for most applications. They are not expensive and have far better peformance than the original paper caps had when new. They have excellent RF characteristics and very low storage factor so can be used in timing circuits. They are available from all the usual component dealers.
    A variation on the cleaning routine is what we used at Hewlett-Packard long ago:
1, Remove anything that can be water damaged.
2, Rinse off with warm water from a hose.
3, Wash with a solution of mild liquid dishwashing detergent, like Dawn, in warm water. We sprayed it from a paint sprayer. A brush or brushes can be used to assist the cleaning.
4, Rinse off using warm water from the hose.
5, Blow out as much residual moisture as possible with compressed air (but make sure the blower is of the oil-free type).
6, Bake dry in a ventilated oven, I think we had ours set at about 130F. We baked for a minimum of 48 hours but I liked to go longer.
   Stuff comes out looking new. 130F is low enough not to damage anything but you should still remove plastic parts.
   Now, we had a thermostatically controlled electric oven, most people don't.  I think one can do well with an oven made of a couple of large cardboard boxes with some holes punched to allow circulation and heated with incandescent light bulbs. Most oven thermometers (from the grocery store) go down to 130F so you can stick one into the box from the outside to keep track of the heat.

On 1/18/2018 4:47 PM, donald collie wrote:
Hi Dave,
Sphere Research Corporation have a document available from their website by
Tek, on how to troubleshoot their `scopes - you might like to read it.
Don`t let this `scope beat you, is the correct attitude, and remember :
most faults are simple - you can see or smell them. Are you sure your
`scope is completely dry? I wash my equipment that I import from eBay in a
bath of hot water, and detergent, rinse in hot pure water, and then dry in
front of a fan heater at about 60 degrees celcius, the hottest you can hold
your hand on, for at least 6 hours, preferably overnight. I usually clear
the faults before washing, as washing can provoke faults. Expect multiple
faults in a piece of equipment this age.Your `scope may have the imfamous
"Black Beauty" paper capacitors in it - these go leaky, and are best
replaced. They are recognised by their shiny [now shiny - you`ve cleaned
them!] black plastic cases. These are best replaced by polyester types. You
have a trace! Good! then you have no serious faults. If the `scopes
performance changes with time : Disconnect from the mains, and dry it out
some more. Make a wind tunnel of a cardboard box, and fan heater, so the
whole instrument gets hot, but not too hot. I think you were wise not to
wet the power transformer - I had a transformer fail once after washing.
Next thing i`d ckeck is the various HT`s for correct voltage, using a
meter, and for ripple/noise, using another `scope. This `scope can kill you
, so be careful. If you have a tube checker, I`d then check all the tubes,
because if the PSU`s aren`t 100%, or you have even 1 doubtful tube, your
pushing it up hill, to find a component fault, so to speak, I`ve just done
a 475 - it had leaky restorer diodes, and 2 defective transistors, which
fortunately weren`t soldered in, buy rather socketed. With determination,
patience, and the humility to ask those who have walked this road before
you, your `scope will be in factory condition sooner than you think. I have
a 547 sitting in storage. Perhaps i`ll start on it soon. What goes wrong
with the 547? The group will tell you.
Good luck, and all patience and determination to you!
Cheers!.....................................................................................................................Don
Collie ZL4GX

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On Fri, Jan 19, 2018 at 1:03 PM, Dave Seiter <d.seiter@...> wrote:

Yeah, sometimes you just have to plug it in and go. Waiting for the relay
to kick in can seem like it takes forever!
It is a great scope!
-Dave
--
Richard Knoppow
dickburk@...
WB6KBL

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