Tektronics 2246A Problem...

Mikebits said:

Just a note, when I worked as a tech rep on Navy ships, 9 out of 10 times my service calls were to repair equipment that had failed, but the original failure was masked due to the ship board tech shotgunning the problem and just swapped and replaced components, all the while the excessive swapping of parts did more damage. I would have to fix what the techs did before going after the original fault.

Point: Take care when replacing parts.

Click to expand...

Point well taken.

Have to say though that back in my day the subs could not go to sea without repaired and calibrated test equipment from our lab. As such, the equipment was returned in working order.

But that was our lab. Can't speak for any others and I don't doubt that happened. Interestingly, however, never saw a single factory tech rep in my seven years.

Just noticed I've been misspelling "Tektronix".

Here is the possible schematic for the 2246: http://www.ko4bb.com/manuals/index.php?dir=Tektronix/Tektronix_-_2245A

Malcomb, as I recall, you probably can't see the mesh from outside the CRT and even if you could, it may be that you'd not be able to see a minor misshapening that would cause the problem. Still, unless the case and related parts were replaced, I'd think that you would see external case evidence of dropping. Had a 465 in the Tek Service Center that had been dropped. Had to replace the CRT, front casting and a few knobs and a couple of TRIGGER LEVEL pots. Swapping out the CRT is child's play. Replacing the front casting is an all-day job.

Power supply fixed...

Well I removed and replaced all electrolytic caps and some other suspect components on the PS board. I re-installed the board and I still get the same result as when I started this project. So, the next thing I did was to connect channel 1 to the calibration point on the scope to get a square wave display. Due to the problem the display is distorted as shown in the original picture I posted. I connected a second scope I have to the +y signal on the tube of the problem scope. I have a nice square wave on the test scope but a distorted wave on the bad scope.

Am I correct in thinking that the problem must be in the tube? My theory is that the y deflection signal is what you would expect, i.e. a square wave but the tube doesn't display a square wave.

Thanks

I replaced the crt in the Scope today and it is now working fine. Thanks for your suggestions and help.

Good job, Malcolm.

And "Thank You" for the update (and info to add to our list of "fixes").

CBB