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I think there may be a few forum members who have access to the HP LogicDart logic probe instrument. I have one which I have recently been using extensively. I would like to ditch the battery mode of operation and go to an AC adapter. Apparently I have put my AC adapter (9100-5557)in such a safe location, that now I cannot find it. The LogicDart owners manual has no description or spec for the AC adapter. On the rear of the unit it states 12V at 0.1 amp , which seems quite reasonable. There is no mention of AC or DC. It is the diagram of the contacts that bothers me. This drawing indicates the center pin as a negative contact and the outer shell as the positive contact, which at least suggests a -12V DC supply which is not a conventional approach but possible. That is not something that I would expect.

I just don't want to connect -12V DC to the unit and accidentally damage the instrument. As far as I can determine HP never released a service manual for this device, therefore I do not know if it is reverse polarity protected. I suppose it is even possible that the device needs 12V AC. I just don't have enough information.

Does anyone on the forum have that AC adapter that they could measure and confirm the contact polarity? Does anyone have a LogicDart with that same diagram on the top rear?

Any information that anyone can provide is really appreciated.

I'm looking at a 9100-5557 right now. It is marked 12V DC 150 mA, tip (center) negative, ring (sleeve) positive.

The applied voltage isn't positive or negative; that has no meaning without a common reference. In other words, you don't have to find a -12VDC supply, as a +12VDC supply will work perfectly well. The requirement is simply that the tip be at a 12V lower potential than the ring. 0V tip and +12V ring would work fine, or -12V tip and 0V ring, or -6V tip and +6V ring.

Of course, this supply should be electrically isolated from the circuit you're testing with the LogicDart; with a wall wart this will generally be the case.


Thanks very much for the info. You have confirmed the diagram.

I understand, that of course, everything is relative to the reference, but I thought it odd that the center pin would be the reference. That is a little unconventional in my experience, but no reason why it should not work.

Now I can strap it to a bench supply and leave it running full time. I was getting annoyed by the automatic turn off after 5 minutes. I cancelled the turn off in system settings and of course 2 nights in a row forgot to tun it off manually. Now I can quit wasting batteries and just run it off a bench supply.

The information available from the members of this forum, once again, proves invaluable.


I wish the LogicDart had been more commercially successful, so that I could buy the new Agilent LogicDart II now.

Hi Donald,

I am not sure if the Agilent page Logic Dart User's Guide can help you.


hpnut in Malaysia

Agreed. It is one of the handiest little gadgets I have ever owned. It would have been great to see it evolve over time. Somehow I got the impression it was not developed in house. I was always interested in the design of the unit but could never locate any schematics. I think that the $800.00 initial price was what killed it. At about half that it would have been wildly successful.

Thanks for the info. I do have the manual but the manual gives no details on the AC adapter. Eric has provided the details I need so all is good.

Actually it was developed in-house at HP, and some of the people involved were from the calculator division. Eric Vogel of HP gave a presentation to the Philadelphia club on June 5, 1997. Jake Schwartz has information and photos here.

Interesting| My assumption was based on the lack of documentation. Usually HP eventually releases documentation after an instrument became obsolete and the warranty period expired. Not so with this instrument. I just assumed they didn't possess the doc's. If they exist, I cannot find them. I may try to get that video.

In the 1990s HP moved toward keeping the innards of some test instruments secret, as had been done from the outset with calculators.