I think group member Milan Vasic has some CLIP files (Component Level Information Packet) that contain schematics for various HP gear including the ESGD B variants of these signal generators. These are proper schematics and they are not in the service manual. HPAK do sometimes release CLIP info into the wild, but sadly not often enough.
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I'm not sure if there will be much difference in the display between A and B variants so it might be OK to work with the B schematics in your case?
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There's an example CLIP here that shows part of the display for the B variants for example:
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This may be of some use but Milan Vasic may have something more relevant?
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In case it is of any interest, my D4000A was running very early firmware when I bought it and the firmware had a nasty bug that showed up when doing an IQ calibration. Instead of muting the RF output it briefly turned the output to full unlevelled and this could get close to +20dBm. This could be enough to damage some test gear. This was not a nice feature...
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I upgraded to later firmware and this seemed to cure this issue. I just checked and the latest firmware and the loader SW is still available on the Keysight website.
