03-21-2022, 09:28 PM
Hello everyone, the other day I traded an old Reel-to-reel tape recorder to a friend of mine who is also a fellow electronic hobbyist like I am for a couple of 1970s vintage HP Signal Generators, one is a Model 8640B and the other is an 8654B and they both came from a local high school that they used to use them for an electronics repair course they had there years ago that they just now got around to cleaning out their storage unit that had all of this old equipment in it that my friend was able to get his hands on these old signal generators.
Anyways these old HP Signal Generators have some strange quirks to them, the 8640B has an issue with an intermittent audio level control for the test tone so that when the unit is set to certain frquencies for the radio to pick up, the test tone is not audible unless you fiddle with the audio level control knob, the way the control acts, it acts like its a dirty pot, but when I opened up the signal generator, I took a look at the pot, and its completely sealed and there's no obvious way to get contact cleaner inside the pot, and the pot is held in place from the front with a nut and washer, behind two knobs that are held into place on the pot's shaft with one hex-head set-screw on each knob, and the set-screw takes a hex-key that is smaller than 1/16" and I'm not sure how much smaller than 1/16" it is exactly, as there's only two other sizes smaller than 1/16".
The 8654B signal generator has a broken u-joint going from the front panel knob shaft to the switch shaft for the display meter mode switch, and I'm not sure how I would go about repairing that u-joint, I looked over at McMaster-Carr and they do have u-joints for switches over there but I'm not sure what shaft size of u-joint I need, all I know is that the set-screws they used to hold the u-joints onto the two knob-shafts are hex-head set-screws smaller than a 1/16" and I unfortunately don't have any hex-keys smaller than 1/16" in my set of hex-keys.
Any ideas as to how to go about repairing these signal generators, and what size of hex-key I need to remove the aforementioned set-screws?
Anyways these old HP Signal Generators have some strange quirks to them, the 8640B has an issue with an intermittent audio level control for the test tone so that when the unit is set to certain frquencies for the radio to pick up, the test tone is not audible unless you fiddle with the audio level control knob, the way the control acts, it acts like its a dirty pot, but when I opened up the signal generator, I took a look at the pot, and its completely sealed and there's no obvious way to get contact cleaner inside the pot, and the pot is held in place from the front with a nut and washer, behind two knobs that are held into place on the pot's shaft with one hex-head set-screw on each knob, and the set-screw takes a hex-key that is smaller than 1/16" and I'm not sure how much smaller than 1/16" it is exactly, as there's only two other sizes smaller than 1/16".
The 8654B signal generator has a broken u-joint going from the front panel knob shaft to the switch shaft for the display meter mode switch, and I'm not sure how I would go about repairing that u-joint, I looked over at McMaster-Carr and they do have u-joints for switches over there but I'm not sure what shaft size of u-joint I need, all I know is that the set-screws they used to hold the u-joints onto the two knob-shafts are hex-head set-screws smaller than a 1/16" and I unfortunately don't have any hex-keys smaller than 1/16" in my set of hex-keys.
Any ideas as to how to go about repairing these signal generators, and what size of hex-key I need to remove the aforementioned set-screws?
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