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Old 07-09-2007, 12:54 PM #17
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Default Re: Try to mod a NewWish but no pot?

Well, judging by your test results, that laser is most liekly operating at or above peak efficiency as is - that MUST mean that it uses an APC circuit - in other words, it is using feedback from a photodiode to monitor the current all on it's own, and there is very little you can do to change that, I am sorry


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Old 07-09-2007, 01:54 PM #18
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Default Re: Try to mod a NewWish but no pot?

It's often hit or miss with trying to ID SMD components from their top marks. It looks like the IC may be a dual op amp/comparitor. Q1 & Q3 low Vce sat transistors and the device at Q2 sets a reference voltage (2.5V).

It's harder to work out the functioning when you cannot see the traces under the components, but it looks like the circuit functions as expected on feedback from the photodiode, compares it to what it wants to see from the reference voltage divider and modulates the current to the laserdiode via the transistors.

You could try modifying one of the voltage divider resistor pairs (R8/R9 or R3/R?).

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Old 07-09-2007, 02:37 PM #19
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Default Re: Try to mod a NewWish but no pot?

Hmm I see no photo diod on this thing, I even took the brass casing apart. I dont think it uses photo diod for feedback on this one.
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Old 07-09-2007, 06:15 PM #20
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Default Re: Try to mod a NewWish but no pot?

How many "legs" are connecting the circuit board to the diode assembly? If there are three, one is for the laser diode, one for the photo diode and one is common.

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Hmm I see no photo diod on this thing, I even took the brass casing apart. I dont think it uses photo diod for feedback on this one.
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