Hi All,
I thought I'd share the repair that I'm doing on my Agilent E4406A Vector Signal Analyzer. I picked up this unit as part of a great test gear auction haul (you can catch the videos here:
Part 1,
Part 2 which includes an awesome 7090A Measurement System, and
Part 3).
I really wanted to get the signal analyzer because I'm hoping that the demodulation capabilities of this and it's PC software will help me in a project I have planned.
I should apologize for the image quality as I didn't actually take any images (I should have) but I recorded a video of the work - These images are stills from that video.
Turning the system on showed the self tests which all passed - Pretty positive:
So I tried putting a 50 Mhz, 0 dBm signal into it and saw this:
Maybe it was something to do with the input attenuator:
Nope - Bummer - It still looks like it is 15 dB or so down and I've exceeded my knowledge of the machine (FYI The HP Yahoo group is an awesome place for guidance on any HPAK gear - Highly recommended) - Based on suggestions, the first step was to check out the block diagram which shows a 7dB attenuator connected to a relay and then into the mixer:
A few people suggested that it might be that attenuator or it could be the relay - Time to start pulling the machine apart - The internal shield has a cool diagram on it showing roughly the layout - Well thought out design:
First thing to check was that 7dBm attenuator - You might be able to see it where my finger is pointing here:
It's more visibile with the front cover off in the bottom right:
Here is what it looks like taken out - 7dB 5W made by Weinschel:
Unfortunately this turned out to be working fine - Here you can see it connected to my E4418B & 8657B:
Now it was time to look at the actual RF board - Here it is out of the machine but still in the enclosure:
And with the enclosure removed - The input part is in the bottom left corner of the board:
Time to check out the schematic - This shows AT1 being the solid state attenuator, U38 being the solid state relay and Z2 being the mixer:
The key piece of information on the schematic is that a 50 MHz Cal signal is switched in to do the self tests. So if the unit is passing the self tests then AT1 should be in good shape. Let's flip the board over and take a look at it - It's pretty funky looking, check out the legs:
Interestingly there were some scratches on the surface of the ICs - I can't see any visible rework on the board so someone either had the board out but couldn't find the problem or they were made during production. The other side of the board shows them on U38 as well:
With nothing visibly wrong I needed to stop and take a think about it, so I produced the first part of the video series on the repair - You can watch it here if you'd like:
https://youtu.be/D7jdur-MGQII'll do another post on Part 2 shortly.
TonyG