Re: Help restoring a 547 scope

Chuck Harris

Just a quick note:

There are no systemic bad capacitor failures with the 547. It is
a whole lot newer than tektronix's last use of black beauty
oil/paper capacitors. Its electrolytic caps are very good.

The biggest issues with the 547 are:

1) CRT's HV transformer gets lossy, and causes the HV to
drop after the scope warms up.
2) metal canned germanium transistors grow internal short
circuits... probably tin whiskers.
3) tunnel diodes in the trigger sometimes change threshold
causing the trigger current to need readjusting. In the
extreme, the tunnel diode may need replacing.
4) tubes, yeah, well you knew that. Thankfully, Cathode Interface
problems were pretty well tamed by the time the 547 came along.
5) dirty transistor sockets.

-Chuck Harris

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!
Collie ZL4GX


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!

From: felix_cantor via Groups.Io <>
Sent: Thursday, January 18, 2018 8:24 AM
Subject: Re: [TekScopes] Help restoring a 547 scope

ok.... ignorance is the mother of all mistakes. It worked!

god! i love this scope.... the trace is so sharp! Amazing.

now i need to fix all the other issues.

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