HP 8656B Stepped Attenuator troubles. Solved

[zebulon1]

No output
It started out getting weak and intermittent.
I think I broke it.
Several years back I converted the back panel output to the front panel.
It seemed to work fine.
This afternoon I opened it and found the RF conduit from the attenuator output to the front panel D connector twisted and in the way of the bottom PCB hinge.
While sorting things out I twisted the attenuator RF output off.
I actually think I probably damaged it way back. It was a mess before I moved the panel connector. I should have left it.
Anyway.
Can this be salvaged?

The RF connection seems looks a pin socket arrangement. I just need to solder this RF connection back on.

 

[rcs16]

Yikes. I need a refresher, been a while since I worked on one.
How did it get twisted off?
The output of the attenuator, the part that broke off, was it semi-rigid coax? Or a SMA?
Show a pic of both sides of the part that broke off so I can see what you are dealing with.
The output connector on the front/rear panel, is a type "N".
Probably should have contacted/emailed me directly. I doubt anyone on AK has ever worked on a 8656B.

 

[rcs16]

does your attenuator look like this pic from the service manual?
So you broke A9J4 off?

 

[zebulon1]

I was able to solder it back using a small butane torch.
The SMA fitting has a ceramic insulator.
It's all back together with the actual HP feet. I used the Marconi 2350 to check the operation and its spot on.
I also took the time to go through the faceplate control board, cleaning and lubing the buttons which were problematic through the years. Checked all of them using a meter for good continuity.
The one thing I noticed is whenever the generator is plugged in, its in standby. There's no indication of it being in standby on the front panel. I might not use it for months. Kinda torqued me off I didn't read that in the OM. The Owners Manual is something I really need to check out better. Particularly, using the stepped attenuator setup. Mine is still what it was set up with when I got it.

 

[rcs16]

Very good.
Marconi 2305 modulation analyzer? Nice
Makes sense to have standby power, it's for the high stability 10MHz crystal oven temperature stabilizer option. Put it on a power bar if you want to switch it off, instead of pulling the plug in the back.
IIRC the crystal oven takes hours to stabilize.
I have a printed service manual from way back in the Motorola days. The damn boss was throwing them out because we had so many of the them. I grabbed one thinking maybe I'll be able to afford one later on, years later when they are auctioned off, out of warranty. Mine came from a eBay member, went to his house to pick it up. he was a Motorola EE that was laid off, they auctioned off the lab test equipment to the staff. It had a calibration sticker, failed AM cal, I determined it was a Motorola 10-bit DAC, mc3410, in the AM modulation level ckt. I was lucky enough to have one in stock. I have a non-op spare if you need any parts. Of course the attenuators are missing.

 

[Bill Ferris]

I was able to solder it back using a small butane torch.
The SMA fitting has a ceramic insulator.
It's all back together with the actual HP feet. I used the Marconi 2350 to check the operation and its spot on.
I also took the time to go through the faceplate control board, cleaning and lubing the buttons which were problematic through the years. Checked all of them using a meter for good continuity.
The one thing I noticed is whenever the generator is plugged in, its in standby. There's no indication of it being in standby on the front panel. I might not use it for months. Kinda torqued me off I didn't read that in the OM. The Owners Manual is something I really need to check out better. Particularly, using the stepped attenuator setup. Mine is still what it was set up with when I got it.

FWIW, I would plug it into a Kilowatt, etc, and monitor it`s standby current/wattage consumption to see what the reference RF oscillator`s oven`s circuit consumes, and decide if it`s standby current/watt draw is uncomfortably "vampire" high and go from there, if no owner manual specification standby current info is available.

Like rcs16 indicates those reference crystal ovens take a few hrs. to fully warm up & stabilize, and longer if the unit is initially cold powered up & especially operating in cooler winter time temperature environment.

Just a suggestive thought.