Repaired! Agilent 33120A AFG question

[WattsThat]

I think I’m on my way to becoming a certifiable TEA member...

Just received a nice condition Agilent branded 33120A and while it appears to function, the encoder seems wonky to me. When attempting to use it to set a frequency or output voltage, it requires a counter-clockwise/anti-clockwise rotation to increase the value, clockwise to decrease. This is certainly backwards compared to the HP power supplies I have of the same era. Yes, I know, open it up and have a look. Just haven’t gotten that far.

Is this normal for this device or does this instrument have a problem? The user manual is no help, it doesn’t mention which direction of rotation is required when changing a value.

[J-R]

Mine is clockwise to increase.

[Someone]

Many types of rotary encoder wear out and behave poorly, replace it and it should come good.

[WattsThat]

Yep, I put the scope on the output and both channels are behaving badly, noise and not changing state in a predictable manner. Time for a new one.

Thank you for the confirmation of proper operation.

[WattsThat]

Surprised to find it was a mechanical encoder, Alps brand. Upon disassembly, it was obvious the unit had been over lubricated and the grease, which looked and smelled like petroleum jelly, had migrated everywhere, contacts and encoder disc included.

Cleaned everything, re-tensioned one of the three contacts so they had the same profile, applied a thin film of de-oxit and reassembled. Good as new until the next time when I’ll replace it.

PS: getting the encoder out was more work than repairing it. Remove the front panel assembly then pop out the translucent window in front of the vfd with three latch points along the top of the panel, remove the encoder nut then slide the pc board off the three detents that hold the keyboard area in place. Obvious once you’ve done it, not so obvious from the outset with no help from the service manual.

[J-R]

Any good software for this that works over serial?

[james_s]

I haven't tried the serial port on mine but I was able to control it using EZ-GPIB with an Arduino based GPIB to USB interface.

Haven't (yet) found a simple way to load waveforms onto it though, a script in EZ-GPIB or a Python instrument control library I found look promising though.