HP 8165A adjustments - Page 1
Forum section: electronics / testgear

author: Buga
author_rank: Newbie
timestamp: February 13, 2013, 03:52:37 am
content: Hey guys,I recently acquired an HP 8165A, and while testing out its functionality, I noticed that it's duty cycle in the 1kHz to about 3kHz and 10kHz to about 30kHz is wacky. The sine wave ends up skewed, and the 50% duty cycle square wave is closer to 30% duty cycle.I am unable to find any reference to adjustments for the duty cycle in the service manual, so I was wondering if anyone here has any knowledge on the matter.Thanks!

author: Skimask
author_rank: Super Contributor
timestamp: February 13, 2013, 06:35:40 am
content: WOW!http://lmgtfy.com/?q=hp+8165+adjustmentYou can't search it with Ctrl-F, but it's all right there.

author: free_electron
author_rank: Super Contributor
timestamp: February 13, 2013, 06:48:42 am
content: Very funny skimask.. If you got nothing usefull to add please shut up. buga has the service manual.Now, here is what i think is going on ( i've never fixed a 8165a but am familiar with this 'series' of machines ).These machines generate a triangle using two current injectors. A sine shaper then translates this into a sinewave and a co parator translates the triangle into a pulse. Since both your sine and pulse are wonky my guess is there is something wrong in the current injectors.Page 8-61 in the service manual shows you which relays are actuated in what mode. The slope control is done using relays. If one is stuck or does not actuate you will have an assymetrical triangle and the sine and square will be weird...The range control is also done with relays by switching around capacitorsCheck that stuff out first... Oh and, make sure you are set to 50% duty cycle on the front panel...

author: Skimask
author_rank: Super Contributor
timestamp: February 13, 2013, 06:51:20 am
content: And you and I both know that half the time, the O/P really does NOT have the service manual (or has the wrong one, perhaps the "user" manual)...the other half the time the O/P hasn't bothered to really go thru it...and the other half of the time...well, that last remaining .00001% actually has an issue...

author: free_electron
author_rank: Super Contributor
timestamp: February 13, 2013, 07:13:15 am
content: Since Buga posted he has the service manual.... i can only takes his word for it.Post that say 'google it' are not very helpful. It is to be assumed that any hobby electronics enthusiast buying test equipment and trying to adjust it has at least two braincells. You only need one braincell to use google.But, even having the service manual is not a guarantee for being able to fix these machines. Some of these hp machines contain incredibly clever stuff or obscure techniques and you really need to read the entire manual and study it. They use a lot of current driven stuff as opposed to voltage driven things and that makes measuring thing very difficult.Troubleshooting this kind of machine without a modicum of experience with similar machines may take days or even be out of grasp for a first-timer.The fact buga is asking where the 'adjustments' are tells me he doesn't know the operating principle ( current injection and sine shaper) . Pointing him to google is useless as you won't find the answer there... . there are no adjustments.. not in that range...There is two possibilites to find the answer : the service manual(which he has) or someone that knows these machines. While i am not familiar with this particular one i know some of its 'generational equivalents'. I quickly looked up the service manual, doublechecked that uses indeed the principle i am familiar with from its family members, and found page 8-61 that describes the ranging and slope switchover. None of that suff could have been found by google as google is not a service technician and has no understanding. It is a mindless search machine. It doesn't know the family members of the 8165a so it can't cross correlate.The other option would be to go to the yahoo group on hp/agilent test equipment and hope someone has had this problem , posted it and another person answered. I quickly scanned the group before delving into the manual. Nothing similar to bugas' problem. Other problems plenty.So also there google would have found zilch.People post questions in the hope of finding answers. Telling them to 'google it' is not helpfull at all and shows you didn't put any effort in even trying to help. It's like receiving a pre-printed answer letter where they just fill in your name. We can do without those. They end up in the vertical file with all the other nonsense and spam.

author: Buga
author_rank: Newbie
timestamp: February 15, 2013, 03:34:38 am
content: free_electron,Thank you very much!The issue appears to be due to the first capacitor that gets switched in for the 1kHz and 10kHz range. The thing I do find strange is that only the rising ramp has the issue, but looking at the circuit, that would imply a capacitor has an issue charging that it doesn't have discharging, or that the extra capacitance loading causes the positive current source to behave non-linearly. The relays are functioning correctly.Your push in the right direction was very helpful! Thanks!