It's all OK now, I took it apart and fixed it :) :) :)
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On the DSP/ADC module A3 the 5V rail is now 4.97V (was 4.70V typical) and the 3V3 rail is now 3.24V (was 2.97V and very drifty).
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I disassembled the main firmware and worked out how it does the power on testing of the power supplies and this gave me the pass/fail limits for all the supplies.?
I was able to trace through the power supply distribution and see where it was losing voltage in a poor connection. A thermal camera helped a lot here. It's now all fixed and fine again!
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I also found out a few things about how it manages the internal 10 MHz reference and how to adjust the high stability 10 MHz OCXO. So that is now calibrated.
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I am so pleased, I thought it was slowly dying on me. There's no way I could afford to send it to Keysight for repair.
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I should be able to fix the other E5052A as well as it has a similar issue with a sagging 5V and a sagging 3V3 supply.
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