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SIPEX CHIP DAC 9377-16-4 NO LONGER SOLD, BUILT A REPLACEMENT USING T.I. DAC712

Our old Leybold e-beam controller acts weird: its 24-pin DAC chip is corrupted and no longer gives trustworthy output voltages. (Weird! the values of the internal resistor chain must be changing over many years!) No DAC-9377s to be found anywhere, but first check ebay.

I find that the Texas Instruments DAC712 (digi-key) is fairly close match to Sipex 9377-16-4, but different pinout. I can build a little hand-wired adapter board that carries the DAC712 and plugs into the 9377 original socket. Differences: the DAC712's /CLR pin needs to pull up to +5, so I add a 4.7V zener and 33K on the 10-volt ref-out of the DAC712 pin-5. I ground A0 and A1 to make it behave as a transparent latch. The MSB pin has to be inverted to map the negative values to positive, so I make a simple inverter to drive "DB15" pin-13 using a 2N3904 transistor. The new gain and offset trimmers go on this little board (see DAC712 spec sheet, while the original ones on the main PCB are now unused.)

Works great; our controller HV output is again accurate to a fraction of a percent.

Now the T.I. part isn't on Digi-key! DOH. Mouser neither. But several on ebay.