Faulty HP 10007B scope probe witches hat question - Page 1
Forum section: electronics / testgear

author: PlaneSailing
author_rank: Contributor
timestamp: March 23, 2022, 06:58:25 pm
content: I have an HP 10007B scope probe with a witches hat problem and looking for advice.At rest (on or off the barrel) the metal tip is 0.1" proud of the normal position in the groove. The hat will actually rattle if you shake it. When the hat is on the barrel and not "compressed" the witches hat will fully rotate (the metal tip staying still), then needing careful aligning with the groove for normal operation. Please see photos.It is like the spring inside the hat is not as long or springy as it was. In theory, the metal tip could be extended and curved 0.1" "earlier", and then possibly 0.1" surplus cut off the end - but am sure I could not do this neatly. Looking inside the hat I can see deep inside a "cross" - not sure if it unscrews for access/maintenance/manufacturing ?.Has anyone else seen this issue with a scope probe witches hat ? - thanks.

author: tautech
author_rank: Super Contributor
timestamp: March 23, 2022, 07:21:10 pm
content: The hook has been bent or twisted.Try closing the hook gently with pliers so it retracts fully into the hat.

author: PlaneSailing
author_rank: Contributor
timestamp: March 24, 2022, 02:41:57 pm
content: Hi, thanks for the reply. The scope probe is in great shape, as new, and don't think the metal tip of the hat has been bent/twisted. The hook curve shape is similar to another HP probe I have - and would rather not try and bend the hook as would probably mess it up.Is it possible to take witches hats apart ?, if so, think stretching the spring, or replacing it would restore normal operation. If anyone has disassembled a witches hat, preferably HP, would be interested in advice, thanks

author: tautech
author_rank: Super Contributor
timestamp: March 24, 2022, 08:47:48 pm
content: Quote from: PlaneSailing on March 24, 2022, 02:41:57 pmI beg to differ as the hook should fully retract into the hat which going by your pic it certainly doesn't.Clip it on the probe and fully extend it and with a medium/large set (better control than a small set) of pliers ever so gently bend the hook shank so it fully retracts into the hat. If it won't then the hook also needs closing slightly.

author: PlaneSailing
author_rank: Contributor
timestamp: March 25, 2022, 01:06:34 am
content: Hi, appreciate the advice.... yes the hook should fully retract into the hat groove. The reason it is not I think is due to a weak / short spring rather than a bent hook.With the hat off the probe, the hook can be pulled with a fingernail 0.1" high, per the enlarged photo, then with the slightest tap or wiggle of the plastic hat, the hook will fall down into the plastic grove if positioned above it. With the hat on the probe, the plastic part of the hat "falls down", can rotate and be out of alignment with the hook. A longer internal spring would I believe prevent this.I can imagine inside the hat is a spring, and in my case it is weak / short. I tried putting a screwdriver inside the hat to see if it unscrewed - but with no luck. Thinking the hat is fabricated with a metal "cap" attached to initially a straight wire, a spring put over it, then inserted into the plastic piece (sort of retractable ball point pen style). The spring then compressed, and a special tool used to curve the end of the wire into the hook, which keeps it together.Believe my options are to straighten the hook, have it all fall apart, find a new longer spring and reassemble, hoping I can remake the hook OK, or per your advice carefully bend / shorten the tip. Anyone seen this problem before ?, thanks.

author: tautech
author_rank: Super Contributor
timestamp: March 25, 2022, 03:06:52 am
content: Carefully inspect around the brim of the hat and underneath for signs of a latch/catch as they can be hard to see.Usually there's 2 catches and pressing them can release the guts of the hat and allow you to restretch the spring however all probes are different but most you can get apart with a little shagging around.If not replace the thing or intermittent connections will drive you nuts.https://www.ebay.com/itm/313875149996?hash=item49146ab4ac:g:GZwAAOSw-DhiCf8x

author: PlaneSailing
author_rank: Contributor
timestamp: March 30, 2022, 06:25:19 pm
content: Thanks for the advice, I could not see any latches or catches inside my HP 10007B scope probe hat. So carefully straightened out the hook, and as expected central metal "core" and a spring fell out, see photo. I carefully stretched the spring by 3mm, cleaned off the 40 year old grease/graphite ?, applied a small drop of new lithium grease, and reassembled making a new hook slightly lower. It now works more as expected, and the plastic hat does not "rotate round". Not perfect, as with home tools you cannot get the metal "pin" straight then bent as HP could in the factory - but it's a lot better. If anyone else has the same problem suggest try carefully bending the hook first before dissembling (I was interested to see inside), as disassembling may not be necessary. Good luck !..... this problem can drive you crazy.