Tektronix 2755 repair

Picked up a Textronix 2755 at a flea market recently for a "hefty" $60 USD. It looked to be in reasonable condition (nothing that can't be reasonably attributed to a couple of decades of service). Absolute worse case there might be some savagable RF components and for the price, I'm willing to ignore the big dot sticker on the front.


No big suprise that nothing happened when I first plugged it in and pushed the power button. So before diving in I did some searching for schematics. ArtekManuals had all the user and service manual for just a tad over $25.

There was also a helpful repair notes by ke5fx.

Power supply

Armed with the schematics I popped the power supply out and started probing measuring things with a multimeter.

There was rectified AC but the primary side switching was completely dead. It wasnt long before I tracked down the dead zener that was suppose to be regulating the 10V that supplied the primary side switching. Looks like there was a previous attempt to repair it by reducing the resistor feeding the zener. Undoing the 'repair" and swapping in a new 10V zener got the 10V rail back up and running.

But no further signs of life.

Next dead component turned out to be one of the pair of power transitors that switched the primary side. With no reasonable way to get a replacment for the original part, I opted for a modern replacement with some 'repair not restoration' fixes.

Modified heatsink
Modified heatsink

The heatsink was updated to also accept a TO-247 package and dropped in a pair of BUV48A.

As a precaution, all the ripple filtering caps for the output rails were replaced.

With the repaired power supply reinstalled I eagerly powered on the 2755.