is my 300 mw blue labby DOA?

[Docjohn]

Thanks Rob, and Zuff. I learned more about grounds.

I'll take some pictures and label them. I really appreciate all the input so far from all the PL members.


John

[stanwax]

Thats what we are here for - and hell what else would we have to do an a Saturday night?

Rob

[Docjohn]

A little more data. Making and breaking the connection between -12v and +5v to create and destroy the rail does not change anything that is stated in post #44. Same voltages and currents are there and the nutty business with the 5v input to the driver PCB.

The only difference is that I can measure 15.1 volts between -12v and +5v when the connection or rail is created. (12+3.1=15.1)

Taking pictures tonight.

Also, I have 2 more bench supplies. Would adding one or more separate additional supplies to the equation change anything, like eliminate a potential problem?


EDIT: Also, when I unplug the laser head at the head, there is no current then drawn on the 5v or 12v supplies. So the driver is not loading the supplies down all by it self.

John

[Docjohn]

Here are some photos of it fired up:

#1 is laser bench
#2 is laser hookup (the DVM is reading across the rail-- 15.26v)
#3 is 12v supply
#4 is 5v supply (shows about 3.1 volts-won't go higher)
#5 is Mod supply
#6 closer up
#7 closer up yet (5v to left--12v in center--mod voltage to right)
#8 closest view
#9 another view

Hope this helps

John

[fuzcub]

It sound as though the bench power supplies are current limiting themselves -
might be some weird grounding issue as discussed. Be carefull about turning the supply voltage up
abouve 5v. If something "comes good" or "goes bad" (failed overheated zener) it might kill the laser.

Ok, try this:
Grab a multmeter and set it to test continuity (so the probes beep when touched together).

With the bench supplies unplugged from the mains supply, test for continuity between the
ground (earth) pin of the mains plug and the negative (0v) on the low voltage output on all three bench supplies.
We're hoping that there's no connection between the input and the output of the bench supplies.Especially the one providing the 5v.
If there is you'll need to find another type of power supply for the 5v rail.

After dissconnecting the supply wires to the driver board, test for continuity between the chassis of the laser head and the -5v, +5v, -12v ,
and +12v points on the driver board.
Also check to see which voltage point( -5v, +5v, -12v , and +12v ) connects with the (MOD -) input.

Connect everything back up and set the multimeter to read millivolts and attach it across the header marked CUR.
When the unit is powered up & idleing (no mod input) you should get a reading . This will be the threshhold current through the diode.Make a note of it.
We can see if the diode is working without using the modulation input by turning up the threshold slightly , to the point that the diode starts to operate.
Turn trimmer P7 ( marked threshold) one turn clockwise, the current measured should rise slightly ( maybe it's counterclockwise),
a faint beam should start to come out of the laser head. If it doesn't happen,carefully try another 2-3 turns.
If still nothing, then return trimmer P7 back to where it started.

If we still havn't much luck, in the next few days I can pull open a system using one of these diodes and make some measurments for comparison.
Or contact http://www.rgblasersystem.com/ directly.

B.

[thesk8nmidget]

ohhh i like your bench!

i need to spend a day there and have you school me on how to use them all

[Docjohn]

understood Fuzcub. Will do.. Thanks


Josh---Come on up. Are you allowed to cross the mason-dixon line? LOL


John

[Docjohn]

the 5v supply had primary and secondary ground connected. It was changed to a supply that did not. So now using 3 supplies with no connection between primary and secondary ground. Made no difference, however, in what was reported previously. The 5v supply still limits at 3.1 v and 8 amps when the head is connected. When the head is disconnected there is no current draw and voltage selection works normally. So things go nuts when the head is connected.

Then resistance readings made:



Resistance between laser head chassis and the following

-5 (1.1K) counts up like capacitance is in the circuit}, but settles at about 1.1K

+5 ( 0 ohms)

-12 (Infinite)

+12 (infinite)


-mod (connects to) -12


300mv across CUR. No change with turning P7 or raising mod voltage

No blue seen of course


Any other suggestions or requests?

Thanks,


John

[fuzcub]

Mmmm I was hoping it would spring to life if it were just a power supply fault.
The 300mv you're reading from the current measurement terminals seems to be a bit too nice a rounded number. Perhaps the multimeter you're using maxes out at 300mv- though most will show "Err" or "Ovr" on the display, or maybe it's not autoranging . Try the next range up ( dc volts) and see if there's a readable value.
Also read ( and post) the value of the chunky resistor(R72) on the heatsink - it should be labeled something like "R050" .
B.

[Docjohn]

The DVM is autoranging and reads from 000.1mv to 1000v without doing anything. The readout is 4 digits.

The thing you refer to is labeled (U32 PBV R050 0.5%)

It has 4 leads. 2 are tied together and go to -5v. The other 2 are tied together and go to T3 the transistor to the right of it on the heatsink. I measure no resistance across it. However it could be .1 ohm. Resistance that low is hard to measure due to the readout jumping from 0 to .5 ohms due to probe lead resistance and varying contact resistance from the ends of the probes to the thing they are measuring.

EDIT: wouldn't it be GREAT to have a schematic of the driver

John