Antique MCA

A friend gave Tim this old MCA that was disused and about to be discarded. Tim took it on as a winter project and enlisted the help of the group one by one. This is a real museum piece from the late 1960. It has a conversion gain of 256 channels and uses *volatile* core memory.

The refurbished MCA displaying a 137Cs NaI gathered spectrum.

The core memory board. Luckily this was still in-tact.

The pulses from the spectroscopy amplified as seen on a period correct, Tek 547 Oscilloscope.

The MCA actually had a digital output to drive a teletype at ~110 baud. The output circuitry was modified to output RS-232 at 1200 baud. But, one of the RS-232 bits was locked high. It just dumped the data one way, there is no handshaking.

Baud rate was confirmed with my inline RS232 protocol analyzer.

We had to trouble shoot the modified communication board, which was deeply nested in the unit. To make matters a bit more challenging, the home-made data lines were all purple without any other form of labeling… (be kind to the next person, even if it is 5 decades later)

Using an oscilloscope with infinite persistence on, one can see that the 7th bit is alway high.

A bit of surgery and we have all bits talking…

To be cute, I started it out, carried on a bit by Brother Lou, then Jimbo, and Brian, we wrote a little HP Basic code on the HP85B to listen for the RS232 dump, save the data, and plot the spectrum both on the CRT and make a hard copy to the thermal printer.

Nice 137Cs spectrum.

Looks about the same.

Mounted it all up in a small relay rack.

The complete 1960’s dream nuclear spectroscopy lab! (thought the HP85B was from the 70s)

We end with a 60Co spectrum.