01.09.2019 In a couple of days I expect to receive a 1GHz probe that i found on ebay personal ads. The lowish price and the long open offer might look a bit suspicious, but due to that I could arrange an even slightly better deal and hope that I´m lucky again. The seemingly low interest could be caused by the fact that the probe was specifically designed as part of the HP54100A/D digitizing oscilloscope system in the late 80s. As such the back front of the small amplifier casing holds not only the BNCconnector but also 6 additional pins for identification, supply and other purposes. It won´t fit on any other scope. But what doesn´t fit will be made to fit (gg)

The service manual of the scope also contains that of the probe. You can read from the manual that 3 pins are reserved for +10V(6), -10V(1) and gnd(5, and BNC outer rim). Pins ID2(2), ID1(3) and ID0(5) are for identifikation. Pin 4 is a second parallel output, decoupled with a 10k resistor and named "Overload Sense".

My idea now is to unmunt the black backside panel and to modify the casing so that only the BNC connector protrudes from the back and that the supply voltages from a laboratory supply or a pair of 9V accus be fed via a additional connector.

As one can see takes the ASIC over most of the circuitry. A Dual OPAmp from PMI (Precision Monolithics, later Analog Devices), a PMI1826 does the Job of Offset-correction and -setting. Unfortunately I couldn´t find anything about this type on the internet. The requirements are rather moderate though.  Typical Offset-OPAs like the OP77 etc. should be useable as replacement.

In the meantime I designed a small dc-dc-converter supply fed via USB and am layouting a small fitting PCB. There will also be a new screening casing so that the probe gets a professional appearance

again.