HP 8644A/B internal battery - Page 1
Forum section: electronics / repair

author: Roy Mercer
author_rank: Newbie
timestamp: October 22, 2016, 01:36:35 pm
content: Does anyone know if the HP 8644A/B RF signal generator has an internal battery that holds important calibration data? I want to buy one of these. However if there is a battery holding important data that I can't replace, I don't want to risk it.

author: siggi
author_rank: Regular Contributor
timestamp: October 22, 2016, 01:44:58 pm
content: I believe the only battery in these is a NiCAD, that's used only to store self-calibration data. This is certainly the way my HP8643A works, if it's left unplugged from the mains for an extended time, it barks a "calibrating" message at me on the next power up. This takes on the order of 10 minutes or so, after which the instrument looks to be in calibration as well as I can measure.

author: Roy Mercer
author_rank: Newbie
timestamp: October 22, 2016, 02:44:31 pm
content: So you believe that if this battery is replaced the entire unit will not need fully calibrated? Thank you for taking the time.

author: Roy Mercer
author_rank: Newbie
timestamp: October 22, 2016, 02:48:43 pm
content: After re-reading your reply I realize that is exactly what you meant. When left unplugged the internal NiCAD battery dies causing the unit to do perform some kind of auto cal. Based off this I think i'll take my chances again. Thanks!

author: siggi
author_rank: Regular Contributor
timestamp: October 22, 2016, 03:45:38 pm
content: Quote from: Roy Mercer on October 22, 2016, 02:48:43 pmYes, sorry if that was unclear.Incidentally, my 8643A came to me in "doesn't power up state", with the PSU in tick-tick mode. The first fault was easily isolated to a module by disconnecting them one by one. Turned out a SMD tantalum capacitor was making like a short on the + or -15V rail. After that she came alive but threw calibration errors after power up. The displayed error was quite accurate and descriptive, as it was complaining of a low 5V rail. These instruments are wired for quite extensive self-testing, and the 5V rail was indeed *just* out of spec.Re-capping the PSU brought everything back into spec (as near as I or the instrument itself can measure).Artek Manuals have the CLIP, in an excellent scan, although didn't cover the switch-mode PSUs on mine. I believe the 8643A is the only one of the family that has a switch-mode PSU, the others are all linear.

author: Roy Mercer
author_rank: Newbie
timestamp: October 22, 2016, 04:42:25 pm
content: No sir, you were quite clear. That was my fault for not paying close attention.How interesting. I had not known of the 86443 until now. I see it has higher phase noise and a solid state attenuator. I wonder if the SMPS is the reason for the higher phase noise. Even though phase noise is higher it's still plenty low for anything I would need. The specs on these things are "out of this world" good.Thank you for the manual tip. I downloaded one elsewhere but the search function in adobe would not work well. I'll head over there in a bit.Are you aware of a way to know what year a unit was built? Or what years certain models were sold?

author: siggi
author_rank: Regular Contributor
timestamp: October 22, 2016, 05:27:48 pm
content: Quote from: Roy Mercer on October 22, 2016, 04:42:25 pmYes, I believe the 8643 is the "budget" generator of the family, and the switcher is almost certainly lower cost and higher noise than a linear hunk'o'metal supply.Quote from: Roy Mercer on October 22, 2016, 04:42:25 pmMine has a 33X serial, so built in 93.You probably know this already, but these things are huge and heavy. I measure 23 inches of depth just for the case. The power supply cowling and front panel knobs then add at least another inch.Sent from my iPad using Tapatalk

author: Roy Mercer
author_rank: Newbie
timestamp: October 22, 2016, 06:43:38 pm
content: Ye sir I sure do. Thank you for pointing that out in case I wasn't aware. I have an HP 5371A and the weight and dimensions are quite close.

author: grifftech
author_rank: Frequent Contributor
timestamp: October 26, 2016, 02:23:24 pm
content: I suggest that you replace the battery to save you 10 minuets every time you plug it in.