PSG E8257D-540 troubleshooting
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Hi all,
I was attracted to this group while googling around Agilent IC part #s. I stumbled upon the following thread?/g/HP-Agilent-Keysight-equipment/topic/synthesizer_module_in_esg/28079593?which had a lot of excellent info that will no doubt prove useful in this Agilent synthesizer repair journey.? Now to the heart of the matter. I recently bought an Agilent branded E8257D-540 in (almost) perfect condition with some good options. The synthesizer works but has two problems which I identified. The first was sporadic loss of output at lower frequencies (randomly between 950-2000 MHz). The RF output across all bands is synthesized from a 3.2-10 GHz YTO. Since this only occurs sub-3.2 GHz, that RF path is directly traceable to the A6 Frac-N. Replacing the original A6 Frac-N with another from a different PSG cures this problem.
Reading the ESG repair thread carefully, I'm 90% sure that at least one of the two 1GC1-4210 which divide the incoming YIG RF are to blame for this. I will have to try probing these microwave dividers once I have a spare moment to power the A6 outside the unit with no covers and investigate. I've taken some high resolution pics of the A6 Frac-N here (PSG service manual also on here): https://drive.google.com/drive/folders/1bfuvlu2nFoTb8uSpvdKbUk0NGnOv90ml?usp=sharing
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The other problem has me stumped. When switching the instrument into ramp sweep mode (it has option 007), it experiences a 508: Frac-N loop unlock error.?
Running a full self test reveals two errors: a 707 Sweep Phase Detector error (A6-Frac N) and a 605 Sweep Loop unlock (A9 YIG driver). The 707 error is determined to be the root cause by the self test diagnostics.
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I tried replacing the A6-Frac as previously mentioned. Neither A6 board fixes or changes any of the errors (508, 707, 605). I also tried swapping the A9 YIG driver out as well with no perceived changes. I've already installed and reinstalled the latest firmware, including the YIG ramp sweep FPGA driver dsp version.? My next course of action would be to identify where the sweep phase detector circuitry is on the A6 Frac-N and trace the voltages and input signals. I've read the PSG service manual word for word, so I have a decent understanding of the high level operation in ramp sweep mode. The blurb which describes A6 Frac-N operation in sweep mode (page 150 of the?E8251-90359 service guide) details the following: "Sweep Mode: The A6 Frac-N maintains phase lock in sweep mode by providing the frequency correction voltage; in CW mode the A5 Sampler provides the frequency
correction voltage.
On the A6 Frac-N, the RF signal is downconverted to 5 MHz using fixed and
programmable dividers. The RF 5 MHz is compared to a 5 MHz reference
developed by dividing 10 MHz from the A7 Reference by 2. The difference in
phase is integrated and a correction voltage is applied to the crossover circuit
on the A9 YIG Driver. By using programmable dividers, the RF side of the
comparator can be kept at 5 MHz while the RF frequency sweeps. Because the
instrument can maintain phase lock while sweeping over a finite frequency
range, the A6 Frac-N divide numbers are changed at filter switch points and
band crossings."
Now, as far as I can tell, the 10 MHz from the A7 reference and the 3.2-10 GHz from the YIG (fed to the A6-Frac-N from a coupler on the A29 20 GHz doubler) are both present and at the correct levels. Of course, I've checked all the power supply voltages and local power rails at the A6 Frac-N and they are within the described tolerance as per the service manual. What really has me perplexed is that replacing the A6 Frac-N did not resolve the 707 Sweep Phase Detector error, yet all the requisite signals which feed this circuit appear to be present...? |
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Some updates. After browsing carefully on ebay, found a reputable seller for new 1GC1-4210s. A few days later and DHL drops off the parts from Hong Kong. They look brand new, still in the tape and no tinned leads/pads, so I'm inclined to believe these are new parts. Swapped them out on the A6 Frac-N board and the sub 3.2 GHz lowband is working great now!
Unfortunately, this didn't solve the 707 Sweep Phase Detector error I'm still seeing during the complete self test.? I'm also seeing a new error message "310: Hardware communication error during ramp sweep".? ?If the sweep phase detector circuit is painfully obvious on the Frac-N board pictures, feel free to spitball any ideas... |
Kevin A.
