« on: February 06, 2019, 05:18:07 pm »
Recent "good" buy on 501J due to 4sd "8" bit stuck on. Seller thought it was intermittent and probably the switch so took a chance. The switch pulls a 74158 input to ground to select that BCD input (8mv on 10v range). Swapping 74158 with another digit did not move problem and measuring at ic showed switch could not pull input to ground. Alpha work around was pull ic and just have that position dead, no output but no problem. Next was pull input to ground with 650 ohm and rest of switches work so only missing 8 and 9 mv. Next day pulled front panel and switch panel prepared to swap switches or flush it or whatever. Plastic toggle appeared jammed to one side and not capturing very short stub on switch. Properly installed toggle and all's well. Now needs "CAL" to limit of existing gear. If the LED is lit, that BCD selection is input to the dac. Pull the chip for no inputs or pull pin low to have the remaining 3 (in this case 1,2,4 for 4SD and 1-15 for 5SD + 6SD SO 1-8.65mv).
« Last Edit: February 18, 2019, 05:17:34 pm by VNUTDENYER »
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HP 3478A, HP 75000-C w/ HP1406A + HP E1410A x2, EDC 501J x6, Guildline 9152/4 Std Cell x2, KEITHLEY 150A Microvolt meter, L&N 4735 W.B., D. Malone 3.0000v ref, DP311 DEKAPOT, CA1569 DEKAPOT, 5KV electrophoresis PS, C.S. 3711A E load, Enviro chamber (truck camper)!?
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