(Fixed) Tek 2445A Small Display problem

[okney1lz]

Has been sitting for a while, but was working, recapped and power supply gone through then.

Now has display, but it's small and centered. See pic.

Readouts are too small to use onboard tests.

Ideas where to look? Horizontal amp?

[rf+tech]

Hi okney1lz,

Your photo shows the scope is stuck in "Beam Find" mode. Beam Find reduces gain of both H and V amps. Cycle the switch rapidly and repeatedly, it may intermittently show the proper display. Clean the switch with Deoxit and see if the problem resolves.

RF+ Tech

[okney1lz]

Had tried that, but will give it another try and clean the switch then report back.

[rf+tech]

The real test is to measure the voltage at U600, U800 pin 15 - or - with the power off, measure resistance to ground.

Per the attached schematic clip, normal operation depends on U600, U800 pin 15 being held at ground via the normally closed contacts in the Beam Find switch.

When the Beam Find switch is depressed (NC contacts open), pin 15 of both U600 and U800 are pulled up to + 5Volts via 10 kOhms.

RF+ Tech

[okney1lz]

Got it sorted! Thanks for the replies.

Traced it out and verified it was the switch, thoroughly cleaned and back up and running.