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HP8640B Range Switch

Graham Member Profile All Messages By This Member #141233 Hi All Does anybody know which fingers on the two range switch sections go to which dividers in the time base section.? My counter appears to work from 0.5MHz to 16MHz and then produces silly results in the counter display.? The counter itself works with an external input to 500MHz, so it has to be the time base selector that is causing problems. I don't appear to have a good quality schematic diagram and pcb layout for this section. I have, using the auxilliary output on a frequency counter, the full frequency range from the oscillators and dividers from 0.5MHz to 500MHz. I have already attempted to repair the range switch with replcement fingers, which *look* like they are connecting to the rotary tracks. I can't confirm this on the ribbon cables though. Any help? would be extremely useful. -- Graham G8ZNK
Bill Riches All Messages By This Member #141234 Hi Graham, One of my 8640 gen fx readout started showing all zeros.? Have not trouble shot yet but can use aux output into a counter for readout.? Your problem made me want to take a look at it.? Film at 11. 73, Bill, WA2DVU Cape May, NJ On Saturday, January 6, 2024 at 05:53:27 AM EST, Graham <graham.g8znk@...> wrote: Hi All Does anybody know which fingers on the two range switch sections go to which dividers in the time base section.? My counter appears to work from 0.5MHz to 16MHz and then produces silly results in the counter display.? The counter itself works with an external input to 500MHz, so it has to be the time base selector that is causing problems. I don't appear to have a good quality schematic diagram and pcb layout for this section. I have, using the auxilliary output on a frequency counter, the full frequency range from the oscillators and dividers from 0.5MHz to 500MHz. I have already attempted to repair the range switch with replcement fingers, which *look* like they are connecting to the rotary tracks. I can't confirm this on the ribbon cables though. Any help? would be extremely useful. -- Graham G8ZNK
Froggie the Gremlin All Messages By This Member #141242 Hello there, the 8640B is a classic HP design, but the rotary switch fingers breeak off and the plastic gears eventually all break. Re switches, Very difficult to get reliable connections, as PCB or fingers can have oxidation or poor tension for contact. Get complete service manual and see switch schematic and mechanical. trace the faulty contact. Gear replacement ...very complex mechanical, Ram in India sells replacement brass gear sets for $55 Life of the old white gear is extended by judiciously reduced speed and number of rotations of band switch, level attenuator, modulation rotary switches. Bon courage Jon See the many sites on 8640B restoration.

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