Check page 5-3 of the Service Guide here - ? .? The Guide is for the 21, 31, 51 Bs but is spookily similar to the 21, 31, 51 As that is on the Keysight sight.? To boot, the B manual is actually OCRed.
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It is not exactly what you asked for, but worth a look.
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Hope this helps,
Bert
