HP8116A *almost* working perfectly

Different make but the symptoms surprisingly the same and rang a bell, nasty to work on IIRC

Philips PM5770 pulse generator Output on 10V setting but not lower settings. Inside the screened attenuator box a secondary switch mechanism comes into action in the 10Volt position but was failing to return on spring action on lower settings.

from my repair briefs file

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Do you have the manual?

Some of the programmable generators use relays to switch pads in and out, to set the output level. They fail, from heavy usage. I had most of them go bad in an old HP 3325B over a couple year period of daily use.

Does it have a switchable output attenuator that should switch at that level? I would look for something like that.

Chris

Yup. Got it, but no schematics on that one...

Thanks! That gave me the clue I needed. I found a number of reed relays and 'scoping out their coil inputs while switching between 9.99 and 10.00 volts noticed that one of them was only getting down to about 2 volts. Traced it back to a 74LS374 octal latch - it's pin 9 output was bad. The chip is located on the bottom board of the 3 stacked boards in the unit. The chip is located on the right side near the front panel when the unit is oriented facing you.

Thanks again, Michael. And thanks to N Cook and Chris as well!

You're welcome.

-- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85.

Michael A. Terrell Central Florida