Hi,

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I found an 8673D generator for my lab, and had to do some minor repairs (power supply, bad contact problem on a PCB).? It is functional but I'm at the point of doing a more detailed check of its condition, mainly the output RF level.

I did a test on the whole band (.05-26.5 GHz, ALC disabled, auto peak reactivated at any frequency change), the attached graph shows 3 curves:

in green, a test in bypass mode (no YTF in the loop or other additional filtering),

in blue it is the normal mode with YTF,

and finally in black, an extract from the hp datasheet showing the typical maximum available power value (ALC disabled).

The green dotted line shows the HP specification for the bypass mode and the blue dotted line shows the normal mode (ALC on).

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There are 3 places where the level is out of specification, and according to the service manual, the cause is that the YTM (frequency multiplier) is not correctly aligned.

From 21.7 GHz, a light indicating error 90 appears (AUTO PEAK MALFUNCTION)...probably out of the operating limit.

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Looking at the procedure to be done manually, in the service book, it says that I have to use an MPU connector (part of the hp11726A kit) that I have to connect on the top of the A2A8 assembly module.

Activate the service switch to position 5. Power up the 8673D and make a specific adjustment.

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Does anyone have any information about this MPU connector (part of the hp11726A kit)? Or what exactly is its function?

Or some recommendations about the alignment of the YTM?

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Since there is no power on these connectors (J1-J2), my theory would be, that this connector is simply a loop between J1 and J2 and pin 7 of J1 would be grounded to signify its presence and also to activate a certain configuration (see schematic image).

If pin 7 is grounded, the RMA signal activates the ROM U3 for diagnostic mode (Chip Select of the UV EPROM 2716), and the RMB signal (output enable), under R/W control of the processor and the address decoder.

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-Yves

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