Repairing HP BNC connector receptacle 1250-0252

[mightyohm]

Hey all,

I have an HP 4192A impedance analyzer with four very tired BNC connectors on the front panel. The center pin sockets are splayed out and make intermittent contact with any cables or test sets that I connect to them.  (I attached a photo of the very sad looking center pin socket.)

I'd like to replace the entire connector or at least the center pin socket/receptacle, but I'm having trouble finding information about how the connector is constructed or where i can find a suitable replacement.

The service manual lists the connector as HP part 1250-0252, which was used in lots of equipment from the era.  This part is available from Keysight, albeit at a high price. However, it's not obvious from the service manual or part drawing if the replacement connector comes with a new center pin. Does anyone know if this is the case? Is the center pin considered part of the connector assembly or is it a separate part, and if so what is the part number for the center pin by itself?  My concern is that the center pin might be considered part of the cable assembly that attaches to the connector, which is obsolete/NLA.

Is there a guide to repairing these connectors online? I am having trouble finding much information, which is surprising given how common these connectors are in older HP equipment.

Lastly, is there a cross reference for the connector and center pin to a less expensive and more readily available connector from Amphenol, TE, etc?

[edpalmer42]

I've never heard of a BNC connector being sold without the center socket.  I would be very surprised to see such a thing.

But if you wanted to, you might be able to rejuvenate the existing connector.  The nut on the back tells me that it's a clamp connector rather than a crimp connector.  If you remove the nut, the cable and center conductor should just pull out.  At that point, you can try to squeeze the center socket back together.  Chances of success are slim, but maybe....

Since the 4192A only goes to 13 MHz, I would think that any BNC connector would be adequate.  I find the clamp style to be more convenient, but crimp connectors might be more common.  On ebay you'll find pre-made cables with whatever connectors and cable length you want.  But, since it is HP, maybe a brand name connector would be more appropriate than a no-name connector.

Ed

[orin]

Yes, on those old instruments, the BNC shells were often separate.  They were essentially a clamp rather than crimp type bulkhead connector.

Take a look at this Amphenol:

https://www.amphenolrf.com/000-86350.html
https://www.amphenolrf.com/downloads/dl/file/id/7061/product/427/000_86350_customer_drawing.pdf

I'd guess the 1250-0252 would be shell excluding the nut, washer and gasket.  The instrument probably has plastic insulating bushings.  (Certainly that's how the similar connector on my 3335A worked.)  If you are really lucky and poke around the Amphenol connectors, you might find something that would work... I'd undo the nut at the rear of your connectors and measure the length of the contact and compare it against the Amphenol parts.  I failed for the 3335A.

All the rear parts from the contact on came pre-installed on the cable.

I had a dreadful time with a similar connector on my 3335A when I converted from a rear to front O/P.  It turned out that they'd used different size shells for the rear output, so the shell I had didn't work with the cable (so if anyone wants the cable for the front O/P on a 3335A, I have one).  However, the whole assembly was just an SMA male to BNC rear-mount bulkhead connector.  I had WiFi Expert do a custom cable: SMA Male - LMR100 - BNC BIG BULKHEAD for the very reasonable price of $11.09.  It worked perfectly with the existing plastic bushings.

I don't know if the cable lengths are critical on the 4192A - they might be but I'd have thought there would be a way of calibrating them out.  Anyway, if you can't find a contact that would work, I'd be looking at getting some custom SMB-BNC bulkhead cables.

Orin.

Edit: Added picture.

Bottom- cable for front connector
Top left- cable for rear connector
Top right - shell for rear connector

[pigrew]

I suggest just finding a replacement BNC to whichever pigtail to replace the existing one. Keep in mind that the outside shell likely should not be connected to the instrument chassis. At least in the newer 2MHz instruments, it uses particular shields to cancel various currents. Cable length shouldn't matter much. Be careful that you get a dielectric that can't be easily charged. I think that PTFE would work.

Or, based on the posted photos, try disassembling and fixing your connector. On the other hand, I tried that on a Racal frequency counter, but the center could not be removed without damaging everything. That was a shame since it was a beautifully machined part.

[mightyohm]

The center pin comes off pretty easily, just heat up the solder and it slides out without too much effort.
I would like to reuse the connector assembly if possible, and if I can actually find this socket pin then it would be a very quick and easy repair to replace all four.
I looked through the parts catalogs and ran every potential match through the Keysight parts finder.  Quite a few parts were not in their system, but one part did come up that looks promising.  1250-0051 is listed as a BNC female socket pin and the 4192A is listed as using this part.  I'm trying to get in touch with someone at Keysight to confirm and to place an order because it doesn't look like I can actually order that part through the website.  Fingers crossed.