HP 3458a repair. Need part # & source - Page 1
Forum section: electronics / general

author: Oldtestgear
author_rank: Regular Contributor
timestamp: April 21, 2025, 12:14:31 pm
content: I still have a few A1 boards that I would like to fix but one part seems to be a common issue on these boards - it's missing. Keysight will not sell it & want to charge for a full repair on a complete instrument. Obviously this is not an option for me, so has anyone got details of Part # 1810-1170 aka RP7? It is described in the CLIP as: 9 NETWORK-RES 9-SIP MULTI-VALUE (28480) 1810-1170. Manufactured by Vishay. I need a few of these so any help greatly appreciated.ThanksPhil

author: Kleinstein
author_rank: Super Contributor
timestamp: April 21, 2025, 12:30:16 pm
content: The part should be RP7, the high voltage divider. This could be a high quality custom part.If the footprint works OK, one could use one the better available high voltage dividers from Caddock, like USVD2.

author: MiDi
author_rank: Frequent Contributor
timestamp: April 21, 2025, 01:19:44 pm
content: Seems Vishay does not offer those kind of dividers at all, so if RP7 is still made by Vishay it is a complete custom part.From the 3458A specs RP7 should have TCR of <1.5ppm and LTD <2ppm/a.USVD2-B10M comes close regarding TCR, LTD is much worse.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 21, 2025, 03:32:38 pm
content: With the ACAL procedure the long term drift should not be important. It would only be the relative TC and related power coefficient that can cause thermal nonlinearity.

author: Echo88
author_rank: Frequent Contributor
timestamp: April 21, 2025, 06:29:27 pm
content: Id assume its most likely a version of the Vishay VTF series:https://www.vishay.com/docs/60038/vtfstd.pdfGood quality Nichrome, cheap compared to bulk metal foil and the 1kV range spec wasnt that important to them/ACAL only needs a short term stable divider, so it wont be a bulk metal foil resistor anyway.Minimum order of 25 pieces applies for this when ordering from Vishay as far as i know, so maybe the USVD is the better deal for only a few A1 boards.Wonder why they are capable of speccing +-0.01ppm/V VCR here and just give a way more conservative spec as < 1 ppm/V (typical) for the TDP1603 series.

author: laichh
author_rank: Regular Contributor
timestamp: April 22, 2025, 03:31:04 am
content: The closest off-the-shelf divider you could get is perhaps the Vishay CNS471 series.https://www.vishay.com/en/product/60043/DigiKey does carry a 5 decade version:https://www.digikey.com/en/products/detail/vishay-sfernice/CNS471A5/10746258It is not a drop-in preplacement, you will need to figure out the pin mapping.

author: Oldtestgear
author_rank: Regular Contributor
timestamp: April 22, 2025, 01:14:05 pm
content: Thanks to everyone that contributed & gave me food for thought. I finally managed to persuade one to come free of the PCB in one piece & there are actually 3 pins connected (9.9MOhm & 100KOhms). Now all I need to do is find a part that is an equivalent. The Vishay VTF range is a good match except the maximum resistance is too low. Caddock makes a suitable equivalent -- USVD2-B10M-010-02-ND -- which may be acceptable in practice. The big question is would anyone be willing to buy a board using the Caddock part?I have been able to do a functional test on boards with 10MOhm & 100KOhm resistors which means I will have a degree of confidence that these boards are usable IF a suitable part is fitted.Comments very welcome as I am not sure if it is worth spending more money on these boards.CheersPhil

author: coromonadalix
author_rank: Super Contributor
timestamp: May 06, 2025, 09:29:28 am
content: if you sell a board and be honest about the needed part(s) i don't think there is a problem, if you a clear and precise from the startif originals are hard to find or no longer available and a substitute can be found or does exist, simply tell a future buyer about themif any repairs on a pcb is clean and no damage, i would not be afraid

author: Oldtestgear
author_rank: Regular Contributor
timestamp: May 07, 2025, 09:04:39 am
content: Code:if you sell a board and be honest about the needed part(s) i don't think there is a problem, if you a clear and precise from the startThanks for your comment.If I get any A! boards that are close to working without the dreaded RP7 resistor. I will offer these clearly stating what is needed & the level of testing I did.CheersPhil