How to test a RF Gen board out of circuit

[NY2KW]

I have a R&S SM300 RF board that appears to have a bad HMC307 digital attenuator.  There are 4 of them that control the RF level output (-125 to +13 dBm) and each can attenuate in 1 dBm steps from 0 - 31 dBm.   Service manual is useless and no schematics available (i called R&S) Picture is attached.  The HMC307 has control lines that are controlled by (-5v).   The HMC307 datasheet is also attached.   

I know what has to be done - tie in Vee and a GND then test each control line while providing a input signal and look at the output on my SA.  The issue for me is the space is so damn tight. 

Any advice appreciated

Jerry NY2KW

 HMC307.pdf (207.97 kB - downloaded 82 times.)

[NY2KW]

sorry here is the picture

[PA0PBZ]

Are they controlled from the same board or from somewhere else? If it is from the same board you can probably not override the lines without the chance damaging the controlling stuff? On the other hand, if they are controlled from outside you could maybe pickup the control lines...

[NY2KW]

It has a PC control board (Linux) for display and remote.  The generator is made of 2 boards, an analog and digital.  No schematics so hard to say where the control circuitry is located but it is probably located on the PC control card or the generator digital board.  The attenuators are on the analog generator board.   Any advice how to work in such tight space around each HMC307?

[PA0PBZ]

There is some kind of controller IC (D8) on the analog board:



The control lines for D8 are coming from the digital board:



Maybe it is possible to use the control lines if you are able to find out how they work?

"Service manual" is here: https://elektrotanya.com/rohde_schwarz_rs_sm300_vector_signal_generator_sm.pdf/download.html

[chick0n]

I built an Extender Cable for the RF-Board, out of this:
https://www.amazon.de/gp/product/B071794QXD/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Works great. You have to cut it for 30Pins.