[attachmentid=361][attachmentid=362]I need help.I just bought a tek tas220 20mhz scope.(don't ask me why)It worked fine for about ten minutes.Then the display went crazy.The display is blurry,unable to focus and is exagerated.This seems to be a common problem with these scopes.I'm new at this electronic stuff.I poked around inside for loose connections and possible cold solder joints.I'm hoping someone has some suggestions,besides tossing it in the garbage .I would appreciate any help.THANKS. powellsd@cox.net .

 

That would be kinda difficult to diagnose without proper schematics and service notes, could be caused by a number of things. When you say it worked for a few minutes do you mean that when you turn it off for awhile ( a cool-down period) and then turn it back on it works again for a few minutes ?

 

Originally posted by Nettron@Jan 22 2005, 10:34 PM
That would be kinda difficult to diagnose without proper schematics and service notes, could be caused by a number of things. When you say it worked for a few minutes do you mean that when you turn it off for awhile ( a cool-down period) and then turn it back on it works again for a few minutes ?

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S.powell,1/22/05,10:55pmThanks for the quick response.It does it continuously.From first power on.Hot or cold.I got it off ebay.I unpacked it and it had beautiful traces.After about ten or so minutes it went blurry.That was yesterday.I fired it up tonight to take the attached pics and it was blurry from the start.THANKS.

 

Hi,

Tek likes to use voltage quadruplers for the CRT high voltage. Yours is probably current enough to have semiconductor diodes rather than vacuum tube rectifiers.

It's lots of fun to check one of these out. Current handling is very small, so any leakage in a capacitor, or an open junction in a diode will drop the HV and cause the CRT to bloom and get fuzzy. Try getting an equivalent capacitor and shotgunning it through the chain. Pray it's that, because the diodes are hard to find.Use care in working around the CRT - it can hold a lethal charge even with low voltage present. The trick is to use a clip lead with one end attached to the chassis, and the other to the metal shaft of a long, small screwdriver. Hold the insulated handle and slip the blade under the boot where the HV snaps into the CRT. You'll hear a pop when the HV jumps and discharges to the screwdriver. Leave it in place for a couple of minutes to be sure, and it's safe to work with the HV circuit.