Older PHI scanning auger systems use the model 97 SED preamplifier to obtain secondary electron images. Occasionally you will not be able to get a TV image on your scanning auger system but are not sure what the problem is. This post will explain how to test the 97 SED preamplifier to determine if it is working properly or not.
For purposes of this test, we will run the J3 video output from the 97 SED preamplifier directly to the TV monitor video input. If you have a 660 or 4300 scanning auger system where the image is displayed directly on the PC monitor you can leave the J3 cable connected.
- Turn off the 32-100 electron multiplier supply main power. For 660 and 4300 systems, turn off the card rack power.
- Disconnect the J1 NEG and J2 POS cables from the 97 SED preamplifier. That will remove the high voltage from the preamplifier and ensure that there is no risk if electrical shock.
- Carefully remove the 97 SED preamplifier from the SED feedthrough flange. Hold the 97 SED preamplifier firmly when loosening the screws and lift the preamplifier straight up and off of the SED flange so that you do not risk breaking the ceramic feedthroughs on the SED flange.
- Remove the J3 video out cable and connect a BNC cable from J3 video out on the 97 SED preamplifier to the Video In on the back of the TV monitor. If you have a 660 or 4300 scanning auger system, disregard this step.
- Note the position of the COL tab on the 97 SED preamplifier as shown in the pictures below.
- Turn on the 32-100 electron multiplier supply or card rack power supply.
- Make sure that the 32-100 SED voltage is turned to OFF and the SED voltage knob is fully CCW. On 660 or 4300 systems, after going through the turn on sequence set the SED voltage to Zero in the scanning dialog box.
- Use a wire or screwdriver and “tickle” the COL tab on the 97 SED preamplifier.
- When tickling the 97 SED COL tab you should see a significant amount of noise on the TV monitor. If so, then the 97 SED preamplifier is working properly. There could be contrast or gain issues with the preamplifier that may not show up with this test, but essentially you can rule out the 97 SED preamplifier as the reason that you are not getting a TV image.
On 660 and 4300 systems this test may be inconclusive as the 79-170 or 81-175 scanning electronics may have a problem on the video board. If you do not see noise in the TV dialog box when performing this test then you can monitor the J3 video output on the 97 SED preamplifier and except to see what appears as high frequency noise in the range of 0 to +2V DC when the 97 SED preamplifier COL lead is being tickled.
If the 97 SED preamplifier test passes but you are not getting a TV image there are a few other possibilities.
- No TV raster. An easy way to test that is to acquire an elastic peak in the point mode and then turn on the TV with a low magnification. The elastic peak should become jagged if the TV raster is working properly. You can also use an oscilloscope and measure the waveforms on the end of the CMA deflection cable.
- No SED voltage. You can use a high voltage probe and measure the voltage between the NEG and POS cables that connect to the 97 SED preamplifier. CAUTION – high voltage is present! Refer this test to qualified personnel who are trained to work with high voltage.
- A defective or worn out electron multiplier. If you have a megohmmeter that can measure over 100 Meg ohms (many meters can only measure resistance to 20 Meg ohms) you can measure the resistance between the NEG and POS feedthrough on the SED flange. Typical resistance for a good electron multiplier is 80 to 120 Meg ohms. If the resistance is 150 Meg ohms or higher the electron multiplier should be replaced.
- Use care when remounting the 97 SED preamplifier to the SED flange as the SED feedthroughs can be easily broken. Make sure the 32-100 or card rack power supply is OFF when reinstalling the 97 SED preamplifier or cables.
RBD Instruments provides repair services and loaners for the 97 SED preamplifier, and we also provide the electron multipliers. If you need help diagnosing problems your system or parts, please visit our website at rbdinstruments dot com.