I just dug out my 5216A Manual. Attached here are pics of the power supply schematic and the board layout to start with. Let me know what you need specifically, and I'll try to get good pics for you.25 CPS wrote: ↑Mon Aug 07, 2023 9:55 pmThanks for the suggestion. I had been giving some thought to how the miscount is present whether the counter is running off the internal timebase or external 1 MHz because this implies pretty strongly that there's a problem taking place outside of the internal timebase. A noisy power problem would affect the whole machine for sure.mansaxel wrote: ↑Sun Aug 06, 2023 11:52 amCheck the supply crapacitors. I've read about more than one counter that had power rail ripple and added 50 or in your case 60Hz and its overtones to the result. Depending on the timebase trigger frequency the outcome varies, of course.25 CPS wrote: ↑Fri Aug 04, 2023 2:19 am
I'm beginning to suspect a problem downstream of the internal timebase. This counter takes a 1 MHz reference input so I couldn't directly connect it to my 10 MHz reference distribution but I used a signal generator that is locked to it to generate 1 MHz out and it was still off.
I did get a bit more playing time with this counter and I also wasn't able to adjust out the miscounting by varying the frequency of the external reference off 1 MHz either. I'll check the power supply performance on it next whenever I have another chance to play with it. The other possibility that comes to mind is the division and counting network downstream of the timebase source. It's possible something in there could be damaged; hopefully that's not the case because power supply components are much easier to source than difficult/unobtainable HP parts. The other thing I need to do is see if there's a better scan of the manual out there than the one on the Keysight website where the illustrations did not come through well at all.
![Image](https://photos.smugmug.com/Electronics/HP-5216A-Electronic-Counter/i-Xf98rxL/0/e8c6dc4b/X3/2023080800573125-4857549290206237937-X3.jpg)
![Image](https://photos.smugmug.com/Electronics/HP-5216A-Electronic-Counter/i-DwPgw5H/0/6b0283f5/XL/2023080800573125-7159061616136300480-XL.jpg)
-Pat