HP 8165A goes a little crazy

Nov 14, 2003 3 Replies
I

I bought an 8165A function generator on eBay and, while the function generating stuff appears to work fine, the display is a bit wacky. It works fine for a few minutes, but then both single LEDs and the seven-segment displays start to do goofy things (like staying lit when they are clearly deselected, and showing 0000 MHz). I have some thoughts on why this is happening - of course, it sounds like some sort of thermal intermittent - but the 8165's control board is not easy to get to *unless* you have the magic extender board.



That's why I'm here. Does anyone know where these extender boards might be found?



While I'm here: has anyone else experienced this sort of problem? Any suggestions? I'm not averse to replacing a "usual suspect" IC and hoping for the best. Thanks in advance for any advice you can offer -- Ian


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J

You have a schematic or service manual? If not, try here:

formatting link
Click on the free manual link, and sign up for free. They might have one.

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E

owners manual and programming guide on ftp://ftp.agilent.com/pub/callpub/EOS/1998/8165 if you don't already have them... erie

works

be

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I

Thanks for the pointer. I have the service manual, which I obtained on CD from this very helpful guy named Dave Miller, and I've printed up the schematics of the board in question. I think it comes down to the way the

8165A maintains state for the displays (both the 7-segment and the individual LEDs in the buttons): it has two RAM chips that hold state information and are scanned to refresh the displays. I suspect that there is some gremlin that is causing the RAMs to be written to at inappropriate times and/or with incorrect data. The unit responds to its pushbuttons and keyboard just fine, and does exactly what I tell it to (including the sweep functionality, which is very cool), but just "forgets" what the displays should say. It's also interesting that if I do something that refreshes the 7-segment - for instance, modifying the frequency - the correct information does reappear, but then goes away again once I hit another button.

Still looking for the extender board.... -- Ian

clearly

intermittent -

hoping

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