MAC 2000 Wash Movers F1ER Light Sensor Fault

[paul_g_787]

We have a whole bunch of Mac 2000 Wash movers here all developing the same fault F1ER.

In each of the MAC 2000s the light sensor (connected to no. 41 on the loom) has yellowed over time (presumably due to the UV from the lamp over time) which I believe is the cause of the fault.

I have verified this by swapping a sensor from a working unit into each of the faulty units and they work fine after this.

The problem is I cannot identify this component?

I would have thought it is some kind of phototransistor but it has 3 pins and don't they usually have two?

Can any one shed some light (pun intended) on what this component is? 

[SeanB]

You are looking for a side looking phototransistor, though the 3 lead type is not too common, and you need one with either human eye response or visible response, in a clear epoxy package.

[paul_g_787]

You are looking for a side looking phototransistor, though the 3 lead type is not too common, and you need one with either human eye response or visible response, in a clear epoxy package.

The only three pin one I can find is this one here: PL550A

https://uk.rs-online.com/web/p/phototransistors/4557954/

https://www.ebay.co.uk/itm/274338056591

The layout of the metal parts inside look the same as the original one, That is all I can tell really

[paul_g_787]

I managed to have a little poke in the MAC 2000 today.

I took some voltage readings (see picture).

Would I be correct in assuming that on this component the 5V is the power supply pin and that the 2.27V is the data pin?

I need to try to work out if the OPL550 would work as a replacement for this part? 

https://docs.rs-online.com/a9eb/0900766b8025c322.pdf

[Twoflower]

That could be something like a integrated light sensor like TSL235R-LF or a similar device.

Can you measure if there's a frequency at pin 3 that changes if the light the device sees changes?

[paul_g_787]

I haven't got access to an oscilloscope so I cannot measure the signal that way unfortunately.

However I could perhaps measure the voltage and cover the sensor and see if that has an effect?

[Twoflower]

That wouldn't help as the meter will always show the same voltage (DC). Unless your meter is quiet fast as the lowest frequencyis 0.4Hz in case absolute darkness. That is if that is the exact type.

You can measure the AC voltage. If 0V AC that's a different device as no frequency is emitted. If you see approx 5V AC that might be the right device type.

If you have a cheap disposable headphone you can abuse as frequency detector with a series resistor you might be able to hear if there's a light depending frequency. Please note that the frequency can be outside of hearing range (0.4Hz...500kHz).

[paul_g_787]

That wouldn't help as the meter will always show the same voltage (DC). Unless your meter is quiet fast as the lowest frequencyis 0.4Hz in case absolute darkness. That is if that is the exact type.

You can measure the AC voltage. If 0V AC that's a different device as no frequency is emitted. If you see approx 5V AC that might be the right device type.

If you have a cheap disposable headphone you can abuse as frequency detector with a series resistor you might be able to hear if there's a light depending frequency. Please note that the frequency can be outside of hearing range (0.4Hz...500kHz).

Ah yes good suggestion! Next time I am in the theatre I will take AC measurements. I will also check what the DC voltages are on the connector with the sensor board unplugged.

[Twoflower]

But to confirm that the device has the same behavior (light to frequency) you probably need a scope or a frequency meter (some multimeter has that option).

As the sensor is obviously placed in reach of the burner I wonder if the light-range especially the upper end requirement is one important parameter that not easily can be checked.

And as I'm from Germany I'm officially eligible to add some German-Angst: If the self-build replacement fulfills the requirement is unknown. That sensor could be part of the security mechanism preventing to operate the burner outside of the safe operating parameters.