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pmt

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PMT

PMT = Photo Multiplier Tube.

{More things to be added}

Tests Performed to Ensure High Speed Amp Function

If the function of the High Speed Amp is in question it can be tested using an oscilloscope. Monitor test point TP4 on the high speed amp board, and then pins 1,2,3,4, and 12,13,14, 15 of the IC, SN75114N. Each should produce a clean square wave, the frequency of which should vary with light intensity

Disassembly

Removing the PMT Tube with Filter wheel 3 (Mk4 and selective Mk3)

Removing the PMT Tube with Filter wheel 3 (Mk4 and selective Mk3)

  1. Remove the coax cable (1)
  2. Remove the db9 connector (2)
  3. Remove the db9 connectors (1 & 2)
  4. Carefully remove the thermister from the PMT (3)
  5. Remove the 10-32 socket head screws (4,5,6,7)
  6. Carefully slide the entire PMT tube out (Note the orientation when you put the PMT back in later)

Removing the PMT Core

Removing the PMT Core

  1. With the PMT standing up, remove the top cap (Note: It is a very fine thread, carefully remove the lid as there are electronics right under it.)
  2. Remove the two 4-40 socket head screws
  3. Move the PCB board (High Speed Amp) out of the way and Loosen (do not remove) the 3 (1,2,3) 4-40 socket head screws (about 3 turns)
  4. unscrew the threaded plate and carefully remove the PMT core
  5. un-solder the resistor off the post
    1. Tip 1: Due to the old solder, it maybe a good idea to add a little bit of new solder then remove it.
    2. Tip 2: You don't need to completely remove all the solder, once most the solder is gone, use a pair of plyers to move the coiled up resistor off the post
    3. Tip 3: there may be a bit of silicone on it, make sure you remove the silicone first
  6. Put on a pair of gloves!
  7. Remove the PMT's shield to expose the PMT core
  8. Slowly wiggle out the old PMT core

Notes for Reinstalling The PMT

Notes for Reinstalling The PMT

  1. When reinstalling the “new” PMT core note the keyed section of the PMT socket
  2. Once the PMT core and PMT shield is reinstalled, ensure the resistor is soldered back onto the post. This is very important otherwise it will not measure/count well! Add some silicone to it to protect it from shorting it with anything else
  3. All the threads on the PMT are fine threads, be very careful and not cross thread anything
  4. Repeat the steps backwards to reinstall everything.
  5. In step 10, you do not need to thread it until it is tight, the 3 screws will keep it tight from letting it spin. Spin the thread so that the coax cable and db9 is in the correct orientation.
  6. After re-installation, in sure you seal the instrument up with fresh desiccant. It may take a couple of days for the PMT to settle down on the counts and dark counts after being opened up. In more humid location, this may take longer.
pmt.txt · Last modified: 2025/12/18 12:11 by reno