AGFA IUP3 Photomultiplier Tube Amplifier


The teardown of a AGFA ADC Compact Plus computed radiography developer became the basis for a range of reverse engineering projects. A complicated system like a automated developer for computed radiography has a lot of different parts inside. The Agfa IUP3 Photomultiplier Tube unit consists of a signal amplifier and high voltage power supply.

Computed radiography is based on reusable phosphor imaging plates, the plate is used instead of film. The x-ray exposed imaging plate is scanned with a red laser timed to a photomultiplier tube. The PMT signal reads out the single pixels on the imaging plate. The returned light from the scanning laser has different intensity dependent on the amount of absorbed x-ray energy. Therefore the photomultiplier tube can translate this into a 12-bit grey scale resolution.

This article covers the reverse engineering of the AGFA IUP3 PMT module. It contains the photomultiplier tube, high voltage power supply and analogue amplifier.


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AGFA IUP3 Reverse engineering

The photomultiplier assembly sits in a aluminium housing with the tube going out through a plastic cover. The inside of the plastic cover has a grounded layer of mu-metal for shielding the tube from electrostatic interference.

The 15-pin SUB-D connector is the only connection to the module. It is both for supply voltages, input and output signals.

Opening the lid of the aluminium enclosure, the entire  assembly can be taken out with 4 screws undone. The photomultiplier tube is soldered directly to the circuit board. It has a supporting aluminium base ring to sit tight in. There is another grounded layer of mu-metal around the rest of the base.

It is not possible to see any kind of markings or stickers on the tube to identify its exact type. From the number of pins only, I guess this tube only has 8 dynodes and in the computed radiography application this gives plenty of sensitivity. The thick blue glass front window makes is impossible to make out how the tube is constructed on the inside.

The tube is soldered to the circuit board on which the 15-pin connector connects to, upwards sits another circuit board on which the high voltage power supply is. Underneath the tube there is a LED coupled with a light receiving diode. This LED is used for testing the tube.

The different markings on the boards are as follows: AGFA-IUP3 on the main circuit board along with serial number SN 02583 and photomultiplier tube number PMT 111296. High voltage power supply circuit board is marked with AGFA-HV1.

On the following picture of the bottom side of the main circuit board I have marked pin header for the 15-pin connector and the pins connecting the high voltage board to the main circuit board. These markings are essential in relation to the attached schematic.

AGFA IUP3 circuit pinout

The arrangement of pin 1 and 9 quickly shows that it is a meant to be supplied from a positive and negative power supply, from the polarization of diodes and electrolytic capacitors. The +/- 15 VDC power supply is the only power source connected and the +5 VDC house keeping power supply is generated with the LP2951 IC.

  • Pin 2, 6, 10 and 12 is connected directly to ground plane and pin 13 is connected to the ground plane through a 1K resistor.
  • Pin 3, 4 and 11 goes straight to the high voltage power supply circuit board. Pin 3 through a 1K resistor. Pin 3 is the high voltage enable input.
  • Pin 5 is the processed data output from the AD823 op-amp, a signal between ground to +15 VDC is outputted on this pin in regard to light detected by the tube. There is also a pin header near the tube connections where the raw signal from the tube can be taken out.
  • Pin 7 and 14 are not connected to anything.
  • Pin 8 and 15 connects to a DG202 IC which is a quad SPST CMOS analogue switch. Two switches each have their inputs connected in parallel, but only one of the outputs are utilized. Pin 15 activates the test LED with its auxiliary circuitry of the coupled light receiving diode on the second op-amp of the AD823 IC. Pin 8 imposes a +400 mV reverse bias on the negative input of the first op-amp of the AD823 IC and is used to reset the tube output data faster than the fall time of the tube itself so it is ready to read the next pixel faster.

The upside of the main circuit board only has pin header connector for the 15-pin SUB-D connector, 4 electrolytic capacitors and 2 inductors.

From the pin HV9 comes the negative high voltage supply for the photomultiplier tube. The cathode of the tube is connected to a large orange painted capacitor that is tied to ground, to ensure a stable voltage at the start of the high voltage chain.

As more electrons are accelerated from the first dynode to the next and so on, less current is needed to drive them. This can normally be done with a pure resistive divider network between the dynodes. But it has its drawbacks with loss of linearity and output deviation in the region of 10-20% at high output current. A improved divider network uses capacitors to insure stable supply voltage at peaks. Individual power supplies for each dynode can be used to do the same.

The solution on this circuit board is however much more elegant and complicated. A network of resistors are used between the first 4 dynodes and there after capacitors, but load dependent driven transistors are used to linearise the output depending on load and that brings the output deviation to around 1-2%.

The high voltage power supply circuit board has no components on the backside, only a few traces that is marked on the following picture.

From the photomultiplier tube handbooks from Hamamatsu, the requirements to a PMT high voltage power supply reveals that quality control is needed to achieve a line/load regulation at +/- 0.2% and ripple noise/temperature drift at 0.05%.

Pin 3 and 11 from the main circuit board connects to pins HV1 and HV2 and are somehow related as they both goes to the positive and negative input of the TL032A op-amp. The output from this goes to a LM393 op-amp positive input and with negative tied to ground through a 50K resistor. The output of the LM393 drives a transistor that ties the ZVS Royer oscillator to ground and thus enables it to oscillate. The ZVS oscillator uses two IRFL110 MOSFETs, 100 VDC/12 A rating, driving the small transformer through a isolation toroid. The output of the transformer is fed through a Cockcroft -Walton multiplier to generate around -600 VDC.

When the circuit is applied with power it is however only pin 3 that has to be pulled high with +5 VDC to enable the high voltage generator and get the photomultiplier tube circuit running.

From the high voltage output end of the Cockcroft-Walton multiplier there is two 100M resistors, one leads back to the -15 VDC supply rail and the other to the second part of the TL032A op-amp, possible for high voltage measurement feedback.

AGFA IUP3 PMT Schematics

Schematics are divided into a signal and high voltage page. I have not been able to map all tracks and component values.

Experimentation: Getting the unit to run

5th March 2016

After having drawn a fairly accurate schematic from reverse engineering the circuit boards, I was confident to test the module with power on. I was using a power supply with +15 VDC, -15 VDC and GND. On the oscilloscope I have a differential probe on the high voltage supply output on channel 1 (yellow), raw signal output from the photomultiplier on channel 2 (blue) and processed signal output from pin 5 on the main circuit board on channel 3 (purple).

I shielded the window of the PMT with aluminium foil to block out any light

Judging from the house keeping power supply IC that generated +5 VDC and the datasheet for the DG202 analogue CMOS switch IC, I tried my luck with putting +5 VDC on the input pins I had located. This is how I found the high voltage enable on pin 3.

When +5 VDC is applied to pin 3 the high voltage supply is generating -600 VDC.

Now that the module was up and running it was no problem doing a few tests, as the test LED was controlled by the CMOS switch, it was merely to pulse + 5 VDC on pin 15 to activate the test LED and capture a shot of the output pulse. The result was a raw signal of -20 mV and processed signal of +4.2 VDC on pin 5.

To test the sensitivity and assumption of maximum processed output of being positive supply voltage for the op-amp, +15 VDC, I used a LED flash light to blink at the tube through a pin hole in the aluminium foil covering the window. The result was a raw signal of -770 mV and a processed signal of +12.6 VDC on pin 5.

As a photomultiplier tube can be a very sensitive instrument, there must be a explanation on why a blink of a flash light is not completely drowning the tube and giving a maximum output. From the PMT handbooks we can see on graphs for common PMT behavior that the amplification is highly dependent on the high voltage supply.

The -600 VDC this module uses gives a mere amplification of 40.000 times, marked with a red line on the graph. This level of amplification is sufficient for the computed radiography, but for a more interesting task like radiation detection with a scintillation crystal, it is suggested that 1-2 kV is needed and as it can be seen in the marked blue area that gives a amplification of 20.000.000 times and up towards times.

Experimentation: Scintillation plastic for radiation detection

9th June 2016

To conduct this experiment I knew that I needed a crystal or plastic scintillator of a fair size to make up for the low tube voltage with more detector volume. Plastic are the cheapest and for a reason, in the detection of gamma rays, organic plastic scintillators have a low absorption coefficient and exhibit less probability for the photoelectric effect, making them unsuitable for energy analysis applications. BC408 is however very good for fast neutron detection.

I bought a BC408 cylinder piece that measures 50 mm in diameter and is 30 mm thick, this corresponds to a volume of 59 cm3.

I borrowed a unknown square piece from a friend with the measures 32 x 32 mm and a length of 100 mm, this corresponds to a volume of 102 cm3.

The test setup was fairly simple, power supply, oscilloscope and photomultiplier tube with a scintillator on it and covered in 2-3 layers of aluminium foil for blocking out light.

I captured the waveforms in single shot mode and just kept raising the trigger limit to see how high output levels I would get. It was however necessary to use a scan range of about 200 uS to catch the signals and then zoom in for the following screenshots.

In the following screenshots from the oscilloscope is the test done with the square plastic scintillator and  I was able to catch up to 4.16 VDC pulse out of the processed output pin.

In the following screenshots from the oscilloscope is the test done with the round plastic scintillator and  I was able to catch up to 5.6 VDC pulse out of the processed output pin.

The noise floor is well below 200 mV with this preliminary test I do know for now that I have a sensitivity between 200 mV to 5600 mV. To be rough and assume this is the maximum values I had found already, have a step of 100 mV that actually gives me a resolution of 54 steps. This is a much better result than what I expected from the standard setup of the tube, future experiments with a proper data collection setup will reveal much more information about its sensitivity.

Agfa IUP3 PMT module from 2009 using XP3314/FL1 tube

The user bktemp on posted pictures and reverse engineering schematics from his unit.

The transistors in the PMT divider I was talking about are the one between cathode and dynode 1 and the one between anode and dynode 8. Unlike the transistors buffering the voltage divider, those two have a zener diode at their emitter/source pin.
I measured all zener diodes to get a better idea of the voltages and currents in the circuit. Both zener diodes near the transistors measure 6.2V.
I also measured the voltages at both stages and they match the calculated voltages based on the voltage divider around the transistors and the zener voltage. It looks like both transistors circuits act as simple zener diodes using the low voltage zener diode as the reference.
Both 160V and 22V are common zener diode voltages, so I have no idea why they used a transistor here instead of the appropriate zener diodes. Maybe they wanted to be able to adjust the voltage? Or maybe they selected 6.2V because at 6.2V zener diodes have the lowest temperature drift? We can only guess why they did it that way, but it seems the voltages at the first and large stage needed to stay fairly constant regardless of voltages on all other stages.
The current flowing through the voltage divider is around 440uA (at 1200V). This is much higher than the measurement range of the anode current amplifier, so it should give a good linearity even for high DC levels.
They probably needed this because when scanning images the circuit must be able to measure large bright sections without having time dependent linearity problems.

Having a flyback converter with no current sensing is often considered a bad design, because it risks blowing the transistor when there is an overload condition at the output.
But maybe it is not possible to use the current ramp due to the additional current draw of the voltage multiplier circuit (in a typical flyback converter, the current during on phase only flows into the inductance of the primary winding, therefore the ramp is linear. But here it has additional peaks making the current waveform useless for peak current control)
The active current limiting circuit starts to limit at around 700uA. That makes sense for a 440uA current draw of the PMT voltage divider at 1200V.
I can not see any connection to the 2.2ohms resistor except between GND (actually -15V) and source of the mosfet. The only way it can limit the current is when the voltage drop gets so high enough the gate voltage seen by the mosfet gets reduced and it goes into linear mode.
That happens at around 5V voltage drop, so the peak current limit is set to about 2.5A. Considering an avarage current draw of the circuit of <50mA, this is a rather high value. The resistor is probably only used for avoiding a self destruction of the mosfet in case the transformer goes into saturation. At that current level, the resistor dissipates >10W.

Using a 0-10V control input voltage, the PMT voltage can be adjusted to almost 1200V. The useful operating range is maybe 500-1200V. Although the datasheet of the PMT says minimum 800V, I have set the lowest voltage to 500V (4.2V at the control input).
At 500V it works fine, but going below 400V the PMT voltage divider current gets too low for the PMT to reach the full range anode current.

How did you plan to get the pulses into the microcontroller?
When researching how to build a multi channel analyzer as cheap as possible wihthout affecting its performance too much, I found two possible solutions:
The first one was using a high speed ADC connected to an FPGA. Based on the pulse width, the ADC needs to have at least 20MS/s to make sure it samples close enough to the peak value of each pulse. The biggest advantage of this solution is the zero dead time, because the ADC is always sampling and the peak detection is done in the digital domain. So after seeing a pulse, it can rearm immediately when the falling slope of a pulse is over.
Today fast ADCs are cheap, but a couple of years back, high speed ADCs mit >10bits were more expensive so I decided for an analogue sample&hold stage, followed by a medium speed ADC.
The S&H stage is basically a peak detector with a reset switch. There is also a highspeed comparator for triggering the ADC when a pulse is detected going above a threshold level.
Then the ADC samples the voltage level and the peak detector gets reset. A small microcontroller collects all the samples. The circuit has a dead time of a couple of microseconds, but otherwise works quite well after a lot of tweaking of the S&H stage.

Feel free to use my schematics/picture on your page. It is always nice to see somebody collecting all the information for such interesting devices.
I knew the PMT came from some medical device, but I had no idea that it was an x-ray image scanner.

bktemp on

Additional information about other Agfa PMT modules [3]

Circuit boards AG-IUP32-8 has a special 15-pin connector which includes a coaxial output.

The following 15-pin SUB-D connector pinout is not verified by myself, but use it as a help if you have to work with the same unit

Coaxial connector is for the signal out

  • Pin 1 Ground
  • Pin 2 -15 VDC supply
  • Pin 3 Ground
  • Pin 4 +5 VDC supply to PIC and EEPROM
  • Pin 7 I2C data connection to PIC
  • Pin 8 Ground
  • Pin 9 +15 VDC supply
  • Pin 10 Ground
  • Pin 11 Ground
  • Pin 15 I2C data connection to PIC

Pinout of the connections for the high voltage circuit board when looked at with SUB-D connector pointing downwards.

  • Pin 1 is connected to PIC Pin 13 (RC2/CCP1)
  • Pin 2 adjust? connected to PIC DAC 1A
  • Pin 3 feedback? connected to PIC ADC? PIC Pin 7 (RA5)
  • Pin 4 Ground
  • Pin 5 +15 VDC supply
  • Pin 6 -15 VDC supply
  • Pin 7 High voltage out
  • Pin 8 Ground
  • Pin 9 -15 VDC  supply
  • Pin 10 +15 VDC supply

Circuit boards AGFA-IUP16 has a normal 15-pin connector and looks very similar to the AGFA-IUP3.

The following 15-pin SUB-D connector pinout is not verified by myself, but use it as a help if you have to work with the same unit:

  • Pin 1 +15 VDC supply
  • Pin 2 Ground
  • Pin 3 High voltage enable
  • Pin 4 Connects to LP2951 +5 VDC power supply IC
  • Pin 5 Processed signal output
  • Pin 6 Ground
  • Pin 7 Not connected
  • Pin 8 CMOS analogue switch, either test LED or positive bias
  • Pin 9 -15 VDC supply
  • Pin 10 Ground
  • Pin 11 Connects to LP2951 +5 VDC power supply IC
  • Pin 12 Not connected
  • Pin 13 1K resistor to ground
  • Pin 14 Not connected
  • Pin 15 CMOS analogue switch, either test LED or positive bias


Reverse engineering the Agfa IUP3 circuit board with only discrete and analogue components is not hard, just time consuming and it takes thinking and experience to make the proper guesses on SMD components as they do not have a unique identification system.

Agfa IUP3 Demonstration

Not yet.


[1] Hamamatsu, “Photomultiplier Tubes – Construction and Operating Characteristics”, January 1998.

[2] Hamamatsu, “Photomultiplier Tubes – Basics and Applications”, Third edition, Handbook, 2006.

[3] V. Baumann and Benedikt H. –, 2013.

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