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Default Tektronix TDS-744A SPC fails

On Sat, 15 Oct 2011 10:18:11 -0500 Andy Cuffe wrote in
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On Fri, 14 Oct 2011 22:04:54 +0200, Reinhard Zwirner

Andy Cuffe schrieb:

May I dare to direct you to the Tek Scopes Yahoo group? You'll find a
lot of Tek specialists there.



That's worth a try. I'm waiting for them to approve me now.

As a side question, has anyone here ever removed the LCD color shutter
from the CRT? I have two similar scopes (a 544 and 744). The 544 has
a mint CRT, but there are some bad spots on the shutter. The 744 has
a lot of burn in, but a perfect shutter. I would like to swap the
good shutter onto the good CRT, but only if I can expect the results
to be good.

Hi Andy,

While I've done a few successful transplants, I would not recommend trying
this. It's a very delicate and difficult operation. The spots you are
seeing on the shutter are due to air bubbles in the optical gel. Usually,
this occurs between the shutter and the CRT itself, but I have also seen
it happen between the glass plates of the shutter. If between the CRT and
the shutter, it is repairable. you'll have to separate the shutter with an
X-acto knife, remove all the gel, clean the surfaces and RTV the shutter
back onto the CRT. If between plates, you'll probably break the glass
trying to separate them. If you do attempt this, be very careful when
removing the shutter that you don't cut the wires that are embedded in the

There's a guy who sells LCD replacement kits if your operation fails.
Expensive, but a well made kit. I've installed a number of these.

As for your signal path failures, I'll bet that one or more relays in the
attenuators have excessive contact resistance. I have found that you can
test them in-circuit in their NC state with a four wire capable DVM.
Anything higher than .1 ohms - replace. You'll likely find some in the 5+
ohm range. I've repaired more than a dozen TDS500, 600 and 700 series
scopes with this failure. Note that you'll need a soldering iron with a
*very* long tip to solder the pins as you have to work under the relays.
You'll see what I mean when you take a look!

For replacement relays, I use Panasonic DS1E-M-DC12V. There are four of
them in each attenuator.

Digikey has them.

Or save some money he

Lastly, if you are running the scope with it's cover off, be sure to run a
fan over the ACQ board as some components get pretty hot.

BTW - I think you were the guy who emailed me the TDS cal software - did
you ever get that to work? (I never tried...)

Let me know how you make out with a follow-up or email is jayw_comark AT