Products > Test Equipment

JDSU J745A spectrum analyser / VNA repair & mini review

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Tiberius1:
Update to previous post.
2 attempts to reflow . 1st attempt failed . 2nd attempt good. Use a good magnifying glass 10x or better to check for good solder between cct board pads and the 2 Rf switch ics just before the 20db attenuator. The soldering around these 2 ic's is the reason for intermittent issues around input signal level.

Hydron:

--- Quote from: ag4zp on May 01, 2023, 04:22:44 pm ---Did you need to change any settings to enable SCPI commands on port 66?  My GC747A allows me to connect to port 66 but does not respond to any commands (e.g., even basic ones like *IDN?).

Also, tangentially related, have you heard of any efforts to reverse engineer the trace file format?  I would love to be able to retrieve S-parameters with these units.

--- End quote ---
Using telnet to talk SCPI on port 66 works on mine, there is a setting in the System->LAN menu (page 2) to set "App Interface" - I selected SCPI (though I didn't try the other settings).

FlexibleMammoth:
Hi all,

I also got my hands on a JD785A.

Did anyone manage to get root on a JD785A, JD745B or JD785B (possibly others from that time)?

JDSU/VIAVI changed the firmware recovery mechanism and the USB script trick from the 745A no longer works. Instead, fw recovery are 2 identical Linux ELFs, plus one system archive with .ko files inside.

Firmware is different yet again, one huge blob with MySQL stuff inside.

The newest 5G devices are different yet again, so no inspiration from there.

BR Andreas

Gri:
Would you happen to know the values of the capacitors C29 and C30 as well as R14 in the preamp circuit? It looks like your photo shows a 551 on the resistor but want to confirm as the chip data sheet seems to suggest a lower value for biasing. I'm working through repairing one now that's been screwed with by someone before and is missing components, hoping I can bring her back to life.

nctnico:
C30 and R14 are some kind of feedback circuit. Likely to flatten the frequency characteristic. The bias resistor for Q1 is R8. Unfortunately I don't know the capacitor values. For C29 100nf will likely work fine.

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