On 10/13/2011 01:11 PM, Hank wrote:
In ,
Scott wrote:
wrote:
I wish you lived a little closer, Chris. I have a Tek 546 scope
(50MHz) with the original cart, original manual, and a 1A1 and
a couple of 1A2 plugins. BTW the scope had developed HV problems
and would lose the trace within about a minute after turnon.
I understand that was a fairly simple problem to fix, however.
I also have original manuals for the plugins.

Most HV problems on those scopes can be solved by scrubbing the thing out
with soap and water and letting it dry thoroughly.

Occasionally you'll see HV rectifier problems and bad ceramic caps, but
leakage from built-up dirt is the number one problem.

Our local surplus dealer in Tidewater, VA just pulls the tubes out of
those things and dumpsters them; he says they aren't worth the money
to drag them out to hamfests and nobody wants them any more.

I actually have a 545 on my bench at work, although the cal guys hate me
and they keep trying to replace it with an Agilent DSO. It just runs
and runs, and it's easier to cal than they claim.

The scopes that Tek made in the 1955-70 era were all-time classics,
particularly the 530-540 series and the later 422/453/454. The real
"go-to" guy on these is Stan Griffiths, W7NI, in Portland.
http://www.reprise.com/ash/clients2/home.asp
Stan's self-published book, "Oscilloscopes: Selecting and Restoring a
Classic" is a must-have for the serious Tek collector.

Stan and I both went to work for Tek in 1960. My career with them was
a bit shorter---three years in engineering, and two as an instructor
in Field Training. What I know about high voltage problems on the
530-540 series fifty years later runs along these lines:

1. The original 531/535 and 541/545 (built through 1959) used "black
beauty" caps in the HV filter. Those are the caps under the cover
over the CRT socket. Replace them. The 533 and 543 were introduced
in 1958 in a later configuration, and the "A" versions of all these
don't have the black beauty problem.

2. The 5642 diodes don't fail all that often---if the filaments light
and they are not gassy, they're probably OK. I believe there are
solid state substitutes available.

3. The HV transformers in the 547 are a problem area, and need
rewinding. There was a guy in Florida doing this in the 1990's; dunno
if he's still around. Can't recall whether this affliction applies to
the other 50 Mhz frames (544 and 546), but my recollection is that all
three used the same CRT and HV setup.

4. On all of them, take the two covers off the HV compartments and
clean them out. I do not use soap and water. Household ammonia on
Q-tips and rags is all the moisture you want to get in there.

On any Tek scope, inspect the wiring under the lower chassis, looking
for hardware that has fallen into the wiring. Tek used 6-32 screws
and lockwasher PEM nuts in construction supposedly secured by Glyptol,
but they come loose and fall into the wiring between ceramic strips.

When you first power one up, have a voltmeter on the heater supply,
and make sure you've got 6.3 volts on power-on. If the heater circuit
is shorted (hardware in the wiring), you'll cook the power transformer
fairly quickly. So it's "on---check voltage---off" on first power-on.

About 20 years ago, I bought a few pickup-loads of these old Tek
classics, and brought them back to life. What I kept for myself was a
533A with a new Tek CRT, a 575 mod 122 (reverse breakdown check), and
a couple of little 310's. These actually do all I need these days.
Also kept a full set of Tek test and calibration boxes that we
actually used when the scopes were new.

Hank



Great info, Hank! Thanks! Hope mine is not the transformer.
I'll follow your advice about the ammonia.

73, David K3KY