HP 3458a repair. Need part # & source

[Oldtestgear]

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.

Thanks

Phil

[Kleinstein]

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.

[MiDi]

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.

[Kleinstein]

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.

[Echo88]

Id assume its most likely a version of the Vishay VTF series: https://www.vishay.com/docs/60038/vtfstd.pdf
Good 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.

[laichh]

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/CNS471A5/10746258

It is not a drop-in preplacement, you will need to figure out the pin mapping.

[Oldtestgear]

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.

Cheers

Phil

[coromonadalix]

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 start

if originals are hard to find or no longer available and a substitute can be found or does exist,  simply tell a future buyer about them

if any repairs on a pcb is clean and no damage,    i would not be afraid

[Oldtestgear]

Code: [Select]

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 start
Thanks 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.

Cheers

Phil