Tag Archives: contact repair

HP 8569B Spectrum Analyzer: reference level adjust repair (broken contact)

A very common fault for the 8569B (and 8565A, 8569A) are defective front panel assemblies because of missing or broken contacts. One particular case is a broken input attenuator switch assembly contact, for the manual/variable attenuation level encoder. This variable attenuation adjustment actually uses a potentiometer (green part), and this mechanically coupled to a BCD encoder, formed by a few contacts and a gold-plated circuit board.

This repair is part of a re-assembly tasks – a gentleman out there had disassembled the switches, and I promised to help out with the re-assembly. But as often, things are a bit more difficult than they first appear, and it turned out not to be only an assembly job, but a repair job.

8569b assembly job

8569b contact repair level adj knob

One of the contact fingers is clearly not making any contact to the circuit board.

8569b contact repair level adj before

To fix, just support the contacts with a piece of circuit board, or other plastic or metal sheet of adequate thickness.

8569b contact repair level adj supported

Then, using 2-component epoxy glue, apply a good amount along the section holding down the contacts. with some contacts still properly mounted, this will hold down the others, for a lasting repair. Sure, you can also use a small amount of JB Weld or similar compound, but I would always advise to apply it evenly over all contacts rather than just trying to fix an individual contact – this will provide added strength.

8569b contact repair level adj

Make sure to properly cure the epoxy before putting things together again. I usually let is sit for close to the heater for a few days.