Products > Test Equipment
Old HP 1651B Logic Analyzer cable question
44kgk1lkf6u:
I assume you are talking about the pod such as this one.
https://bmisurplus.com/product/hp-pod-2-data-k-clock-plus-logic-analyzer-probe/
The large box is a plastic frame that holds the probes together. The probes are detachable. The manual says it is to make debugging fewer signals less messy. With all the probes removed, only a plastic rectangular tube is left. The probe has 2 pins that connect to the ribbon cable. They connect to the blob of plastic via a piece of coax. With 18 probes in total, that is, 16 data, 1 ground, and 1 clock, the 4 outermost holes in the ribbon cable connector are not connected.
The 2 pins plug in directly to the connector on the ribbon cable. They are signal and ground. The ground row is shorted in the connector on the ribbon cable.
The part molded in plastic on the other end of the coax is the important part. It may be hard to persuade someone to destroy it to take a picture. The compensation network is between the center conductor of the coax and the single wire. It is not connected to ground. I only happen to have the service manual for the 16557D. It says on page 149:
--- Quote ---
The probe tip networks comprise a series of resistors (250 Ohm) connected to a parallel combination of a 90 KΩ resistor and a 8.5 pF capacitor. The parallel 90 KΩ and 8.5 pF capacitor along with the lossy cable and terminations form a divide-by-ten probe system. The 250-Ohm tip resistor is used to buffer (or raise the impedance of) the 8.5 pF capacitor that is in series with the cable capacitance.
--- End quote ---
There is no difference between the data and clock probes besides the label.
The picture is from the link.
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