Tuesday, 7 April 2015

Modifying a Packard / Perkin Elmer Photomultiplier PSU

Today i took a deeper look at the packard photomultiplier power supply i removed from the LSA i recently took apart. It has a Packard part number of 7101139.

I wanted to test powering on the PSU from my bench power supply and verify the function of the control input. To allow me to easily use this in future projects. When installed in the 1000 TR LSA 5v was seen on the two input pins which seemed to enable the power supply output at around 1600v.

First i verified the power supply was working. Applied +15v to the power input and +5v to the control line and got the +1600v output i had seen when the unit was in the LSA.

After inspecting the circuit i spotted a MAX584 voltage reference  close to the input with only the 10v output of the reference in use i suspected the board would be adjustable so altered the voltage between 0 and 10v and indeed the supply did alter it's voltage from +970v to +2290v.

I wanted to check the circuit to see if it can be made more stand-alone and still be made adjustable, there are missing trimpots and jumpers on the PCB so wondered if these would allow this.

On closer inspection JMP1 & 2 had a soldered link across two of the three pads with JMP3 unpopulated. These connected the inputs on the control cable connector to the rest of the circuit. In the other position they connected in the two missing trimpots R41 and R42 into the same input.

The pads were cleaned of solder, three pin headers installed and using a salvaged 10kohm trimpot the trimmers allowed full voltage adjustment from +970v to +2150v on each channel. Switching of the JMP3 jumper allows both channels to be turned on or off, but not independently. I maybe able to further modify this two allow that feature.

Soon i will sort out a suitable enclosure, probably with an integrated power supply for connection to the mains and two 10 turn pots to allow voltage adjustment.