"Blue Beam of Death"?

[keebs]

Hey all,

I have 2x 1.8W units from Able and have been having an issue with one:

Shortly after powering the unit on, the blue laser immediately turns on and stays on at what may be full brightness.

I've opened the unit to try and debug and gotten as far down the signal chain as disconnecting the connector on the ILDA board which (I'm fairly sure) sends the analog RGB signals to the laser's power modules, but the blue module still outputs the solid blue beam.


Based on this, I'm assuming either the laser module or the power module has gone bad.

I have 2x units, so I *should* be able to determine where the problem is by doing some swapping... but taking these apart is a bit scary due to the number of cables/connectors/routing etc, so was wondering if anybody on here had any advice/thoughts?

Thanks so much,

Todd

[matratzki]

Is it ttl or analog?
When it is ttl it could be a problem with a floating modulation signal. Does the second diode the same, when removing the modulation signal plug?

[keebs]

Is it ttl or analog?
When it is ttl it could be a problem with a floating modulation signal. Does the second diode the same, when removing the modulation signal plug?

It's analog modulation.

No, the good diode doesn't output anything when the modulation signal plug is pulled.

I guess my big question is, if the diode is on non-stop: is this an indicator of the laser *diode* failing or is an indicator of the laser *driver* failing?

T

- - - Updated - - -

PS - I'm fairly sure it was a bunk surge protector that blew it. Lesson learned.

[ZeroPoint]

My guess would be the laser driver. Depending on whether it is a high side or low side driver it seems you either have power being shorted to the laser or you have a short to ground somewhere. In other words, if it's a high side driver (meaning the driver controls the input current to the laser diode) then it is possible that there is a voltage bypassing the driver circuitry and powering the diode directly. If it's a low side driver (meaning that power is always present at the laser diode and the driver just controls the connection to ground) then it is possible there is a short to ground that is, again, bypassing the driver circuitry. Most drivers that I'm aware of these days are high side drivers as it's safer for the diode. You could take some voltage and resistance measurements to help narrow it down. Check for continuity between the laser diodes ground wire and chassis ground with the projector off. Also check for continuity between the laser diodes positive wire and the drivers power wire and any power wires for fans, TEC, etc, that are also connected to the driver. If it has continuity between both a power wire and a ground wire then there is a physical short somewhere. If there is only continuity between one or the other then it's possible that there's a faulty component on the board that shorts when power is applied. My guess is that you should have continuity between the diode ground wire and chassis ground but not between the diode power wire and any other power wire on the driver (or any other power wire in the whole projector for that matter).

Edit: To fully answer your question, the laser diode is likely just fine. When a diode fails it will almost always stop working completely. I don't know of any situation in which the diode would fail in an "always on" condition. For it to be on it simply needs power (controlled current) and ground. It's the drivers job to decide when the laser should be on or off. If it is always telling the laser to be on, even when you're telling it to be off then the driver is most likely the culprit. There are certainly other ways for this condition to happen but removing the modulation input should terminate the beam. Since you have removed the input signal, all that's left connected is the driver and the diode. See if you can measure any voltage on the modulation input pin while it's disconnected. Obviously, if you disconnect the input there should be no voltage present at the pin. If you do measure a voltage there then the trick is trying to find where it's coming from. If it's not a frayed or damaged wire that's accidentally touching the board or a wire that's been clipped into the wrong port of a connector somewhere then it's probably a failed component on the driver board. Has this projector had this problem since you bought it or is it an issue that just started happening randomly?

Edit 2: Just noticed you mentioned the blue laser is delayed slightly after power-up. Are we talking 5-10 seconds, or a minute or more? Almost all quality drivers will have a "soft start" delay build in to them so that no power can be sent to the laser until all the voltages have settled down after being powered on. This prevents any voltage spikes or in rush currents from damaging the laser when you flip the switch. The soft starts are usually about 5-10 seconds long. If this is the case then it may help point us in the right direction. A physical short between power and ground through the laser would completely bypass the soft start feature (not to mention un-metered current through the diode would probably blow it up after a few seconds anyway). If the soft start is functioning properly then we can conclude that the power causing the laser to be on is still going through the driver circuitry. It doesn't necessarily mean there isn't a physical short somewhere but it may help us narrow down where that short may be.


Luke

[ZeroPoint]

Does the second diode the same, when removing the modulation signal plug?

Perhaps I am a bit confused here. Are you referring to the other red and green diodes or are you suggesting 2 blue diodes? I guess I assumed there was only one blue diode in the module. Certainly if there are two blue diodes and only one is displaying this condition then that helps narrow it down quite a bit.


Luke

[keebs]

Perhaps I am a bit confused here. Are you referring to the other red and green diodes or are you suggesting 2 blue diodes? I guess I assumed there was only one blue diode in the module. Certainly if there are two blue diodes and only one is displaying this condition then that helps narrow it down quite a bit.

There is only one blue diode per projector. I believe he was referring to the other projector that I have

Todd

[keebs]

My guess would be the laser driver. Depending on whether it is a high side or low side driver it seems you either have power being shorted to the laser or you have a short to ground somewhere. In other words, if it's a high side driver (meaning the driver controls the input current to the laser diode) then it is possible that there is a voltage bypassing the driver circuitry and powering the diode directly. If it's a low side driver (meaning that power is always present at the laser diode and the driver just controls the connection to ground) then it is possible there is a short to ground that is, again, bypassing the driver circuitry. Most drivers that I'm aware of these days are high side drivers as it's safer for the diode. You could take some voltage and resistance measurements to help narrow it down. Check for continuity between the laser diodes ground wire and chassis ground with the projector off. Also check for continuity between the laser diodes positive wire and the drivers power wire and any power wires for fans, TEC, etc, that are also connected to the driver. If it has continuity between both a power wire and a ground wire then there is a physical short somewhere. If there is only continuity between one or the other then it's possible that there's a faulty component on the board that shorts when power is applied. My guess is that you should have continuity between the diode ground wire and chassis ground but not between the diode power wire and any other power wire on the driver (or any other power wire in the whole projector for that matter).

Edit: To fully answer your question, the laser diode is likely just fine. When a diode fails it will almost always stop working completely. I don't know of any situation in which the diode would fail in an "always on" condition. For it to be on it simply needs power (controlled current) and ground. It's the drivers job to decide when the laser should be on or off. If it is always telling the laser to be on, even when you're telling it to be off then the driver is most likely the culprit. There are certainly other ways for this condition to happen but removing the modulation input should terminate the beam. Since you have removed the input signal, all that's left connected is the driver and the diode. See if you can measure any voltage on the modulation input pin while it's disconnected. Obviously, if you disconnect the input there should be no voltage present at the pin. If you do measure a voltage there then the trick is trying to find where it's coming from. If it's not a frayed or damaged wire that's accidentally touching the board or a wire that's been clipped into the wrong port of a connector somewhere then it's probably a failed component on the driver board. Has this projector had this problem since you bought it or is it an issue that just started happening randomly?

Hey Luke, Thanks so much for the response. This is exactly the type of experience and advice I was looking for.

This is the first time the projector has had this problem. After re-tracing the events of the evening, I suspect it resulted from (somebody else) plugging the unit into a sketchy surge protector / UPS that was on stage. It may be unrelated, but I noticed that the blue driver is the only one which does not have the ground wire coming to it from the mains, so I wonder if the lack of a return path is what fried it.

Anyway, I think with your advice I at least have some things to try once I tear it apart on the bench, rather than purchase a new diode/driver which was quoted at $450. Unfortunately, the blue driver is at the very bottom of the case, so from what I can tell I will need to take the optical plate off, then a riser on stand-offs with the red and green drivers just to access the blue driver. It should be doable, but will take some time and care considering the cabling and whatnot.

Edit 2: Just noticed you mentioned the blue laser is delayed slightly after power-up. Are we talking 5-10 seconds, or a minute or more? Almost all quality drivers will have a "soft start" delay build in to them so that no power can be sent to the laser until all the voltages have settled down after being powered on. This prevents any voltage spikes or in rush currents from damaging the laser when you flip the switch. The soft starts are usually about 5-10 seconds long. If this is the case then it may help point us in the right direction. A physical short between power and ground through the laser would completely bypass the soft start feature (not to mention un-metered current through the diode would probably blow it up after a few seconds anyway). If the soft start is functioning properly then we can conclude that the power causing the laser to be on is still going through the driver circuitry. It doesn't necessarily mean there isn't a physical short somewhere but it may help us narrow down where that short may be.

Great point. The delay is about 5 seconds or so.

It may be a little bit before I rip this baby apart, but I will update the thread when I do so. Hopefully it will be to simply say, "I got it working!", but it may be looking for more advice

Thanks so much again,

Todd

[kecked]

I have had weird stuff happen with surge protectors and lasers. Something about the ground. Also make sure you have enough current and voltage. That can cause issues.

[ZeroPoint]

It's possible that a poor surge protector could cause some problems but they usually remedy themselves once you plug the projector into a proper power source. There should be no direct connection between mains power and the driver board or laser diode. Mains power should go directly to one or two DC converters inside the projector. A high voltage spike could certainly damage one of the converters but I feel it would be very rare for that spike to make it through to the other electronics. a low or dirty mains signal could also certainly cause irregular behavior from the projector but shouldn't cause it any damage. Once a clean signal is provided the projector should work fine again. I'm assuming the ground wire from the mains (A/C) that you're referring is earth ground. This shouldn't be necessary for the driver since it only needs a D/C power and ground connection. Generally, any D/C electronics find earth ground through the chassis and don't need a dedicated wire. Additionally, while the lack of a proper earth ground might cause some unwanted noise in sensitive electronics I doubt that it would cause the problem you're experiencing. At most it might cause the diode to glow slightly or cause a small fluctuation in output power due to a noisy signal but it shouldn't cause the diode to default in an ON condition.

Out of curiosity it would be good to check the A/C mains voltage at the power supply as well as the D/C voltage from the power supply to the driver. They should both be steady voltages. Without knowing the design of the drivers it's too hard for me to suggest any detailed tests to make other than the basic input/output tests but I think the most concrete test would be to hook up a second driver to the projector. I realize this involves some disassembly but at this point I think the current driver should come out to be bench tested anyway. Keep us posted.


Luke