Troubleshooting an HP 8656B Sig Gen - Any Experts Out There

Started by Hawaii596, 03-11-2008 -- 10:25:37

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Hawaii596

03-11-2008 -- 10:25:37
Hey Folks,

As my lab is in a large customer facility, my end customers occasionally scrap old instruments and offer them to us if we can use them.  I received two HP 8656B Sig Gens the other day, one with front and the other with rear output.  So obviously I chose to check the front output unit first.  And wouldn't you know it, it has problems and the rear output unit looks fine.  So this is low priority, but thought I'd throw this question out to any of you fellow RF/Microwave PMEL types in case any of you have seen this problem.  This is a side project, and so I can't give much time to it.  Below is the symptom (which I have some ideas on, but wanted to see if anyone may know this problem (or even want to guess).

SYMPTOM:  As frequency is tuned across operating range (0.1 - 990 MHz), at certain frequencies, the signal becomes completely destabilized.  For example, at 184.99 (tuning up in 0.1 MHz increments) when I hit 185.03 MHz, signal unlocks and begins sweeping across approximately 100 - 270 MHz.  The signal stays in this unlocked condition until I hit about 187 MHz then locks properly.  It does the same thing when I hit approximately 370.05 MHz the same thing happens.  I checked 740 MHz and the same thing happens.

My theory is that there is a problem in frequency multiplier, or problem at the bottom end of the base band that it isn't providing adequate drive level to the multiplier stages.

Shouldn't be too bad a problem.
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

mdbuike

#1
03-16-2008 -- 07:44:29
You could be right...if there's a YIG involved, and considering the number of phase loops..

Agilent still has the manuals for this..  www.agilent.com then type in 8656B and the go to manuals (about 44 of them if I remember)..if you need any of them, download them now, you may not get them in the future, since this generator is obsolete

Good luck, and let us know..I'm still supporting two of these for test stations (one of which will be my Monday morning calibration..and a PR to boot...ah well, the computer is in charge..I'll just follow directions and kick it when it misbehaves  :-D  )

Have a great St. Paddy's day

Mike
Summum ius summa iniuria.

The more law, the less justice.

Cicero, De Officiis, I, 33

RichieRich

#2
03-17-2008 -- 09:14:01
Start with the easy stuff.  Don't kill yourself troubleshooting a pll just to find out you have an open cap in the power supply causing too much ripple.  Always check your power supply for DC and AC ripple before you get deep into any kind of troubleshooting.
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