3458A: A9 voltage reference PCB mechanical data (03458-66509) - Page 1
Forum section: electronics / general

author: niner_007
author_rank: Frequent Contributor
timestamp: July 13, 2019, 06:49:39 am
content: HiI'm looking for mechanical data on the voltage reference PCB in the 3458A.So far below is what I have, validated from my own measurements against a 03458-66509 from my 3458A, but this data is not down to the last 0.1mm and I'm not super happy with it.PCB dimensions: 50.2mm x 42.5mm (W x H)Drill sizes: about 3.8mm (3 drills, for holding down the plastic cap and the PCB on the chassis); the two drills for the plastic cap seem to be a bit larger by about 0.5mm or so than the other drillDistance between plastic cap drills: 17.2mm, this seems to be fairly accurate, TiN'a data here (17.05mm) fromhttps://xdevs.com/doc/HP_Agilent_Keysight/3458A/cad/a9_cap_drw.pdfis either incorrect or the cap was not made to be perfectly centered in the holes intentionally, for some sort of fit/snap reasonJust to be clear, with the data I have, it will definitely work, but does someone have more accurate data?Thanks!

author: MiDi
author_rank: Frequent Contributor
timestamp: July 13, 2019, 07:48:30 am
content: If you want a replica, there is already one incl. gerbers, but at the moment I cannot find the link.There are several threads about that, you might want to search for it.Edit: I see,you already knew that

author: niner_007
author_rank: Frequent Contributor
timestamp: July 19, 2019, 09:56:05 pm
content: It all fits

author: TiN
author_rank: Super Contributor
timestamp: July 20, 2019, 08:41:37 am
content: I see perfect 0.0 ppm/year LTZ reference right there

author: Theboel
author_rank: Frequent Contributor
timestamp: July 20, 2019, 09:18:50 am
content: hi niner_007Where You buy the LTZ1000 "cap"I hope its not made use 3d printer

author: 3roomlab
author_rank: Frequent Contributor
timestamp: July 20, 2019, 09:21:37 am
content: This is my interpretation of the ref board in simplified versionI drew the outline into eagle for fun (I do not even have a 3458a)left version is the original (I shamelessly copied this from pictures off some posts and from google), including the LTZ strangely off centerthe right side is if the 2 are aligned and shifted to the edge.in both, all main parts and holes sit on 25mil grid exactlyI think the plastic cap being off center looks to me like they "ran out of design time" or something to that tune. because if you slightly shift the LTZ or the cap, it fixes the problem (and save some electrons haha !)look at your own drawing, you can already see the cap is not center with LTZeverybody copies this exactly. I was hoping someone will already do one that is centeredsince your version is mm, everything is not in alignment esp if the error is in 0.1mm. since everything is THT component, everything needs to sit around multiples of 2.54mm or 1.27mm. but since everything in 3458a could be 0.1mm tolerant, maybe it doesnt really matter.edit an updated stolen overlay in PNG with more details (1pixel=1mil). another weird thing (which I guess is common?). the oversizing of TO126 pads so that the pin space is 2.54mm/100mil and not according to the part which is 2.28mm/90mil.the accuracy of the overlay is only as good as the degraded processed photo. but in this version, there is more to see as pins/parts are highlighted vs 25mil grid scale

author: MiDi
author_rank: Frequent Contributor
timestamp: July 20, 2019, 06:41:11 pm
content: There was a theory that the offset could be due to the pin on TO-5 case.It is not, the pin directs to board edge:

author: niner_007
author_rank: Frequent Contributor
timestamp: July 20, 2019, 09:43:18 pm
content: Quote from: Theboel on July 20, 2019, 09:18:50 amit's from the 3458A reference; not sure you can buy it standalone; what's wrong with 3D printing it? you could 3D print it in ceramic if you want (SLA ceramic resin)

author: niner_007
author_rank: Frequent Contributor
timestamp: July 20, 2019, 09:47:08 pm
content: Quote from: MiDi on July 20, 2019, 06:41:11 pmwasn't it so it doesn't get too close to the mounting hole? could be great to print a transparent cap and look at the alignment and position of the LTZ1000 within the cap, or print half of a cap; I have transparent resin, and could try it, but lots of pain swapping the print tank