Hi guys
I'm now trying to repair a high power (1.5W) RGB Laser
The original fault I found was a blown (blackened) fuse and two s/c rectifier diodes on the PSU HT side
Having replaced the diodes the laser then powered up for a second and blew the fuse again (just popped this time)
I then disconnected the feed to the main PCB and powered up the PSU again with a new fuse. The cooling fan worked so I checked the voltage to the main PCB it is +12 0v- 12
So I thin powered up the main PCB from my bench supply. The current limit was kicking in and the PSU was supplying about +5/-5V on current limit. When I increased the limit a bit something suddenly changed and the negative rail stopped drawing power (well it went to about 30mA), the positive rail went to about 0.8A and the unit powered up
All lasers working, and the diffusion grating motot rotating and selecting 'patterns'. The laser diodes kinda flashed on for a second and then and off with each pattern slection.
I noticed however the projected patterns did not rotate as they should - because the X-Y morror motors were not moving
I had a quick look athte main PCB and saw what looked like an output device... in fact it looked like a stereo amplifier chip.... and indeed it was. A TDA7625
datasheet here http://pdf.datasheetcatalog.com/datasheet/SGSThomsonMicroelectronics/mXtzzzq.pdf
I then tried moving the XY mirrors with my finger. They indeed did freely move and I very quickly discovered that a 1500mW laser can actually burn!! OUCH
OK so now using a PCB tool I discovered that once the mirrors are roughly in range of the intended beam direction (firing through the defraction gratings - the lasers switch on. If i then keep waggling either of the mirrors a little bit the beam will stay on. Once I stop moving the mirror the beam shuts off after a second. I take this as a good thing as it suggests the microcontroller is alive and well and that the XY motor feedback circuitry is working.
Both motors check out at around 5 ohms. I then used my bench PSU to power each motor in turn and I can make them move either way by reversing the polarity. All good so far yep?
I then used my scope on the TDA7265 and noted there is no drive going to the motors, but when I move a mirror with my pcb tool, the corresponding amplifier input swings +ve or -ve which suggests to me that the microcontroller is sensing the position change and trying to move it back.
I also noted that the Mute/Standby pin on the TDA7265 is at 11.5V (supply voltage is +/1 12V which according to the datasheet the TDA7265 is in standby
However I kinda thought maybe what has happened is the TDA7265 had a short circuit output on the negative rail to ground, which is what blew the PSU diodes and the fuse in the first place, then once I connected up my bench PSU which has a bit more grunt, the TDA7625 drew more current then went open circuit on the output - hence the sudden current drop. On this thought Ifigured maybe the microcontroller put the TDA into standby when the motors did not move on power up. However this did not tally with the fact it looked like it was trying to drive the mirrors when I moved them
Anyway today a replacement TDA7265 arrived and I fitted it. It made no difference.
My next approach was to track down what is driving the TDA Mute pin .... and I have some pics of the circuit attached
Now my question is this
Shouldn't the transistor driving the TDA mute pin be on, therefore have voltage low on the collector which connects to TDA pin 5 via a 10K resistor and therefore switching the standby function off (TDA7265 outputs powered up)?
The transistor has 0.49v on the base and the emitter is connected to ground (0V) There is another transistopr of the same type 'J6' which has 0.02V on the base and 6V on the collector - however this can't be driving the other transistor base as the diode just to the right is reverse biased. There must be something else connected to the transistor base to pu 0.49V on it. The thing is, both transistors look OK in circuit (both have the same voltage drop B-E B-C on my multimeter which makes me think they are both OK. But then what else could explain the high voltage on he transistor collector unless it is faulty even though it meters out OK? Anything??
I drew some red lines so you can see how this all connects up. R17 is 10K
If there is no voltage drive to the TDA7625 mute/standby pin does it just float high and go into standby on it's own? I have no experience of these amplifier chips
I am thinking now, because the micrcontroller actually tries to move the motors when i waggle the mirrors that it 'thinks' the TDA7265 is not in standby, otherwise why would it do that?. So some problem in the standby circuitry itself?? Maybe that transistor is faulty. I am tempted just to connect a low value resistor TDA pin5 to 0V to force it out of standby and see what happens. Good idea or bad?
Oh the transistors are marked J6 and I think this may be the datasheet http://www.s-manuals.com/pdf/datasheet/s/9/s9014_galaxy.pdf
Cheers for reading this and for any advice offered
Rich
I'm now trying to repair a high power (1.5W) RGB Laser
The original fault I found was a blown (blackened) fuse and two s/c rectifier diodes on the PSU HT side
Having replaced the diodes the laser then powered up for a second and blew the fuse again (just popped this time)
I then disconnected the feed to the main PCB and powered up the PSU again with a new fuse. The cooling fan worked so I checked the voltage to the main PCB it is +12 0v- 12
So I thin powered up the main PCB from my bench supply. The current limit was kicking in and the PSU was supplying about +5/-5V on current limit. When I increased the limit a bit something suddenly changed and the negative rail stopped drawing power (well it went to about 30mA), the positive rail went to about 0.8A and the unit powered up
All lasers working, and the diffusion grating motot rotating and selecting 'patterns'. The laser diodes kinda flashed on for a second and then and off with each pattern slection.
I noticed however the projected patterns did not rotate as they should - because the X-Y morror motors were not moving
I had a quick look athte main PCB and saw what looked like an output device... in fact it looked like a stereo amplifier chip.... and indeed it was. A TDA7625
datasheet here http://pdf.datasheetcatalog.com/datasheet/SGSThomsonMicroelectronics/mXtzzzq.pdf
I then tried moving the XY mirrors with my finger. They indeed did freely move and I very quickly discovered that a 1500mW laser can actually burn!! OUCH
OK so now using a PCB tool I discovered that once the mirrors are roughly in range of the intended beam direction (firing through the defraction gratings - the lasers switch on. If i then keep waggling either of the mirrors a little bit the beam will stay on. Once I stop moving the mirror the beam shuts off after a second. I take this as a good thing as it suggests the microcontroller is alive and well and that the XY motor feedback circuitry is working.
Both motors check out at around 5 ohms. I then used my bench PSU to power each motor in turn and I can make them move either way by reversing the polarity. All good so far yep?
I then used my scope on the TDA7265 and noted there is no drive going to the motors, but when I move a mirror with my pcb tool, the corresponding amplifier input swings +ve or -ve which suggests to me that the microcontroller is sensing the position change and trying to move it back.
I also noted that the Mute/Standby pin on the TDA7265 is at 11.5V (supply voltage is +/1 12V which according to the datasheet the TDA7265 is in standby
However I kinda thought maybe what has happened is the TDA7265 had a short circuit output on the negative rail to ground, which is what blew the PSU diodes and the fuse in the first place, then once I connected up my bench PSU which has a bit more grunt, the TDA7625 drew more current then went open circuit on the output - hence the sudden current drop. On this thought Ifigured maybe the microcontroller put the TDA into standby when the motors did not move on power up. However this did not tally with the fact it looked like it was trying to drive the mirrors when I moved them
Anyway today a replacement TDA7265 arrived and I fitted it. It made no difference.
My next approach was to track down what is driving the TDA Mute pin .... and I have some pics of the circuit attached
Now my question is this
Shouldn't the transistor driving the TDA mute pin be on, therefore have voltage low on the collector which connects to TDA pin 5 via a 10K resistor and therefore switching the standby function off (TDA7265 outputs powered up)?
The transistor has 0.49v on the base and the emitter is connected to ground (0V) There is another transistopr of the same type 'J6' which has 0.02V on the base and 6V on the collector - however this can't be driving the other transistor base as the diode just to the right is reverse biased. There must be something else connected to the transistor base to pu 0.49V on it. The thing is, both transistors look OK in circuit (both have the same voltage drop B-E B-C on my multimeter which makes me think they are both OK. But then what else could explain the high voltage on he transistor collector unless it is faulty even though it meters out OK? Anything??
I drew some red lines so you can see how this all connects up. R17 is 10K
If there is no voltage drive to the TDA7625 mute/standby pin does it just float high and go into standby on it's own? I have no experience of these amplifier chips
I am thinking now, because the micrcontroller actually tries to move the motors when i waggle the mirrors that it 'thinks' the TDA7265 is not in standby, otherwise why would it do that?. So some problem in the standby circuitry itself?? Maybe that transistor is faulty. I am tempted just to connect a low value resistor TDA pin5 to 0V to force it out of standby and see what happens. Good idea or bad?
Oh the transistors are marked J6 and I think this may be the datasheet http://www.s-manuals.com/pdf/datasheet/s/9/s9014_galaxy.pdf
Cheers for reading this and for any advice offered
Rich
