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HP8753D input problem

Question asked by scottrf on Jul 29, 2010
Latest reply on Aug 3, 2010 by scottrf
B input is bad. If I split RF OUT and send one output to R, then split the other output to A and B, the B trace is fairly flat across frequency, but is not consistant between sweeps, and B/R is 35 dB below A/R. My wild guess would be that the first stage input of B is blown.

Downloaded service manuals for ABC models and D. D manual does not have figures, so I hope ABC manual will help with that. Have taken top, bottom, and side panels off. Removed many gopher sized dust *****. Samplers are all 5086-7413 with SN 5164x (x=1,3,5), so I figure they are all original. BroadcastRF, you've just been though some of this, so I wondered if you could give me a jump start in how to remove the Samplers. Looks like I could do an easy test by swaping the input and/or output cables on A or B samplers. From Dr Joel's answer to one of BroadcastRF's questions, it seems like the Samplers are the same as in the A-C models, so if I had to replace one, I could get it out of a scrap ABC?

I've not powered it on yet with the covers off. You must not have to remove covers to do a cal, because it has a 2007 cal sticker on it, but a million years of dust inside. Huge dust wads just fell out when I opened it up.

Also, some of the front panel buttons take a few presses to make them work, so i wanted to see if I could clean any contacts. Any advice on button contact cleaning on a D? Primarily it's the ones on the right of the display.