Any unknown HP 8640B service manuals? - Page 1
Forum section: electronics / repair

author: _rushin_or_draggin_
author_rank: Regular Contributor
timestamp: September 14, 2024, 04:47:40 am
content: Hey all,I am in the process of repairing my HP 8640B and I seem to have a serial number that is right in between all the service manuals I find. I have a 2404a prefix. I have been able to do most of the work on it with the manuals I have found, but I am currently having trouble diagnosing the counter/lock section of the instrument. I have found the 1991 manual listed on the keysight webpage, but it only shows the service part, not any of the adjustments (and it wants an adjustment before any troubleshooting begins if the "pre-troubleshooting check" fails, which is my case). I have checked all of the keysight page as well as KO4BB. Does anyone know of some manuals I might be missing? Or perhaps a complete 1991 issue of the manual with all backdating included?Thanks

author: HalFoster
author_rank: Frequent Contributor
timestamp: September 14, 2024, 09:13:28 am
content: Artek has one (08640-90197) that includes the change sheets that cover that SN.

author: factory
author_rank: Super Contributor
timestamp: September 14, 2024, 10:15:14 am
content: There are some change sheets on the web somewhere dated 16th Feb 1984, they cover prefix 2408A, can't remember where I found the pdf, but it's far too big to attach here.Edit: It's the 59MB file labelled "HP 8640B Signal Generator Service Manual-8640B sup 1" on KO4BB, first page showing the prefix list is attached below.David

author: Stray Electron
author_rank: Super Contributor
timestamp: September 15, 2024, 01:01:56 am
content: FYI before you tear into that 8640 go online and read about some of the experiences others have had trying to repair those. For one thing they are very prone toejectingthe tiny gold springs that are used in the attenuater switches, never to be seen again.

author: Zenith
author_rank: Frequent Contributor
timestamp: September 15, 2024, 10:15:53 am
content: You'll very likely find the plastic gears are cracked and useless. There's lots on the web about dealing with this, and there are brass gears available, but it's all more to do, and more expense.

author: factory
author_rank: Super Contributor
timestamp: September 15, 2024, 11:39:48 am
content: Also check the little internal/external timebase switch on the back, apparently the small toggle switch can get knocked into the external position, when handling this heavy signal generator, this would stop the counter from working (unless you have an external reference hooked up). The same problem I've found with some Venner counters.David

author: _rushin_or_draggin_
author_rank: Regular Contributor
timestamp: September 16, 2024, 05:38:15 am
content: Thanks for all the help. I’ll be sure to check that out. I saw the manual backdating on KO4BB but it didn’t register in my mind to read it! The whole unit functions correctly, it just has some quarks.One being the counter itself doesn’t like to lock over a wide range. I see the manual says you should be able to turn the fine tune knob a quarter turn and it stay locked. Unless I’m turning it too fast, it doesn’t do that. Now it will stay locked by itself for awhile which is all I need, but I’d still like to return it back as close to factory as I can.Another weird thing is the level meter likes to display zero when I turn it on, and only when I crank the output power up to +20 and max vernier. After that it works fine.Finally, the internal counter works fine, on all ranges, but towards the top end of each range it will begin to count back down (while increasing the frequency) and then just zero out completely. Connecting the output to the external counter works perfectly. (Also been verified with a counter and an oscilloscope).It’s just weird stuff like that, but it’s definitely a usable unit as of now.

author: Dave Wise
author_rank: Regular Contributor
timestamp: September 17, 2024, 10:32:07 pm
content: If anyone has "HP 8640B Signal Generator Service Manual-8640B sup 1.pdf" from KO4BB, please upload it here. KO4BB's website seems to be broken right now.

author: factory
author_rank: Super Contributor
timestamp: September 18, 2024, 12:26:15 pm
content: Quote from: Dave Wise on September 17, 2024, 10:32:07 pmIt's too big to add here, 59MB!This was uploaded to the HPAK groups by me in March, I did rename the file, to add the manual part number it is used with & the print date;https://groups.io/g/HP-Agilent-Keysight-equipment/message/142978?p=%2C%2C%2C20%2C0%2C0%2C0%3A%3Arecentpostdate%2Fsticky%2C%2Chp+8640b%2C20%2C2%2C0%2C105108145It's this one;HP_8640B_Signal_Generator_Service_Manual-8640B_sup_1 Manual changes for 08640-90197 dated 16 Feb 1984.pdfDavid

author: Dave Wise
author_rank: Regular Contributor
timestamp: September 18, 2024, 05:17:17 pm
content: Thank you, David - interested people are reminded where they can get it while KO4BB looks for more storage.