A brief summary of the somewhat tedious job of fixing the 8569B front controls, which are a great feat of engineering but the plastics are prone to aging:
First, replacing the gear, it is a 48-pitch, 48-tooth spur gear, glad that I had one spare, but they are still available:
Next step, some contact cleaning, using a soft eraser, and some isopropanol.
The frequency control – for some reason, there are different versions around, one that has wires attached, and one the has pins – interestingly enough, the 8565a control fitted has wires, but the 8569b requires pins – also here, good to have a spare assembly around, with the pins…
Defective bias pot – also here, a spare fitted.
Some of the contact fingers broken off-also there were fixed, and everything put back together.
Finally, noticed that the 10 dB segment of the 70 dB input attenuator (5086-7365) is stuck. Nothing dramatic, just one of the little O-rings holding the contact actuators broken off, and parts of it stuck in the contact.
Finally, a quick test – everything seems to be working-
-unfortunatly, still missing something – the sweep time indicator is not showing a time denominator (µs, ms, sec), and the analyzer remains in the digital mode for all sweep time settings – it should switch to mixed analog-digital mode (at the time the 8569b was designed, there was no easy way to run analog-to-digital converters any faster than a few kHz without causing exorbitant cost, so the 8569b uses the digital storage mode only at the slower sweeps).
(1) Identify the issue with the sweep time indicator and missing transition to mixed analog-digital mode. Maybe related to the 8565a control fitted to a 8569b? – Checked by substituting a control assy from a good 8565a – working just fine with the 8569b – accordingly, this is not the reason for the fault. There seems to be a defect on the main front panel board. Maybe a bad switch contact, or a broken trace. Will be quite a pain to test will all the cables, switches and screws.
(2) Manufacture the control knobs for the frequency-bandwidth-span-atten-ref level setting. These were missing and don’t have spares at hand/these wheels are getting brittle anyway. Will make a new set from aluminum alloy, during next stay, in Germany, the only place with access to adequate machine tools.