Leadlight 110 resistor mod - unsafe

[deezdrama05]

I did the resistor removal mod on 2 110 pointers so far. The pot only works when these 2 resistors are removed and bridged. I got 30mw out of the first unit but the beam is very unstable. Its current draw is 600uA!!!!!!!! Thats way too much and not safe for the diode!!!!! The second one I did this mod on burnt the diode out while i was turning the pot,the red LED lights up but no green beam. This sucks. Has anyone tried using different resistors rather than just bridging?????? Have you figured anything out with these 110 units lasermod?????

 

[deezdrama05]

Nobody has done this mod or has any info to share????

 

[Goldmagnet]

Hi There

The 110 unit is awsome to mod, have a look on the PL board for my mods, or on the GLF for details. I dont short 2 resistors as you say, what are the details of your mod ?

600 uA is hardly any current, did you mean 600ma ?

I have an 80 mw 110 with the 106 cap mod and the 102 resistor mod, these are the only 110 mods I do.

I bought a few 110s from ebay recently and they are not 110s, have a look at the PCB in my mods, is it the same as yours ?

Gold

 

[Corona]

Here's what I know about the recent 110s (with green LED)

After a few hours of reverse engineering, I've realized 2 things. One, my version of the GPL110 is different than that shown around here, the LED is green , not red, the layout is different - but the circuit looks to be similiar. Two, whoever designed this is either a complete idiot - or a total genius.

Here's my schematic, derived from some digital macro photos, head-scratching, in-circuit measurements, and educated guesses.

The ceramic capacitor values are not relevant, but they are probably 100nF or so. Anyway it's pretty straightforward, but after reading several posts that indicate tweaking the pot does nothing, I wondered why. Looking at the circuit a little closer, it soon dawned on me that the voltage drops of the series string LD, Q1, and Q2 would pretty much total 3V. Besides, with Q3 in series with the 1.35V base drive, and Q1 above the negative rail by the saturation voltage of Q2,there is near zero margin to turn ON Q1 - let alone headroom to maintain the LD current with <3V.

Curiosity got the best of me, and by applying about 3.5V from a partly discharged Li-Ion cell, the output woke up noticably. And the green LED was summarily toasted (I replaced it with a better one after the picture was taken). OK then! The design depends on a solid 3V, either by clever intent, misapplication, or just poor design practice.

So using NiMH batteries (their fully charged voltage is lower than alkaline) with this design is doomed from the start, and I really wanted to be able to use NiMH cells.

Since Q1 is the "controlled" pass element, and Q2 is always ON and basically is there to share the dissipation with Q1 (and that is the Good Idea part), with a 3V supply Q2 can be jumpered without any adverse affect (worst-case dissipation in Q1 is under 250mW at ~200mA through the LD). In fact, removing the forward voltage drop of Q2 will allow the pointer to work deeper in the battery discharge curve. So if you want to get a little more battery life out of your pointer, or use rechargables, have a look at the photo and note where the yellow bar is.

If the pot is left untouched, the green output power should remain exactly where is was before, and in fact will be more stable over battery life - because the APC circuit is still doing its job. Note that I do not condone tweaking the pot as this violates the FDC/CRH classification of these pointers! This information is intended solely as an academic study of the circuit.

Here's the rearview of the PCB. This is apparently a new PCB design that AtlasNova is now shipping (black barrelled APC units). The schematic above is valid ONLY for units with this version PCB layout...

Hope this helps, but if you really don't understand it at LEAST understand that the so-called 106 capacitor mod (which defeats the current limit and APC entirely) and any resistor mod that extends the range of the pot to increase the pump diode current beyond 450mA WILL result in damage to your pointer.

 

[deezdrama05]

great info guys!!! Sofar the only mod i found for this was to remove the 102 resistor and jump the connection and remove A106 and jump the connection, but this blew the diode on one of my units because of the 600ma current draw.

 

[deezdrama05]

Has noone realized that this mod brings the current draw to unsafe levels? Theres gotta be a way to bring the current draw under 450ma. I can solder but im no electronics expert but I guess I will have to order some surface mount resistors and do some trial and error experiments. Does anyone know what type and wattage surface mount resistors i need to get for these driver boards?

 

[Corona]

With my little transistor mod, the pointer will servo the LD current all the way to the crystal/diode output power limit. When adjusting the pot, you MUST monitor the laser power (green LED method) and adjust the pot until the power reaches a maximum. Above this point, the LD current draw will increase without bounds as the APC circuit attempts to reach an unattainable output power. I set mine a bit below this point, to provide some safety margin for thermal variations, crystal aging etc. and have had no problems. I am seeing approximately 6-8x the (green LED measured) power as the unmodified, unadjusted unit. So maybe this one is making 35-40mW.

I did have one unit that went multimode on me during mods and testing, this one was making something well over 50mW (conservatively estimated by LED monitor current measurement). I was pushing about 600mA into the LD. It did not recover when the LD current was adjusted down to 200mA - it's now a multimode laser module (odd!). I think the LD was damaged by the excursion, and the crystal was able to handle a higher total power as there were then TWO active laser spots. Hmmmm.

One thing I noted during all this was that the green LED active area is apparently rather small; moving the beam around in tiny amounts changed the microammeter reading considerably - so when peaking the green output, you must take care to be sure you are "on target" with the laser or you will see misleading (low) results.

BTW I use exclusively NiMH batteries in my pointer, and I don't use the modded one for anything outside my home - it's just too risky. It does spin a radiometer amazingly well, but I have not tried melting electric tape

 

[deezdrama05]

These 110 units are odd, after removing 102 and A106 and jumping them the pot has the capability of 650ma of current. But when I set it to a safe level of around 400ma I notice the beam fluctuates badly and the current draw fluctuates from 200ma up to 650ma- these are very odd units. What is this transistor mod you speak of ?

 

[Corona]

Look at the photos I posted in this thread, and verify that your controller PCB looks exactly the same as mine. Then restore it to original condition before modding it "my" way.

My "transistor" mod is simply placing a wire jumper across the yellow bar in the photo, this shorts out one of the series pass transistors, allows the circuit to work as intended down to 2.5V or so with no other changes, and is safe.

If your PCB is different, post some clear, close up photos of both sides of it and I'll find the time to reverse engineer it (I know Leadlight changed the PCB design at least once in the 110s) and post the appropriate transistor mod for that version...I don't think they changed the circuit much, only the layout was changed. Anyway...

 

[deezdrama05]

Mine is different-give me a minute to get some pics....

 

[deezdrama05]

Here is a link to pics of the driver board I have http://www.greenlasers.co.uk/cgi-bin/yabb/YaBB.cgi?num=1111737381
My driverboard is exactly the same except the red and black wires are opposite of where they are on these pics...odd

 

[Corona]

Oh, they changed it a bunch...mine (a newer one?) has reduced parts count and a slightly different approach to the APC. The photos are fairly good but there is no substitute for having the PCB in hand to look at, measure trace continuity, etc.

It looks like they are using two SMT transistors in parallel as the series pass element (to control the LD current), which is very different than my pointer's design. Shorting the A106/C106 capacitor appears to bypass these transistors entirely - very bad indeed.

What I CAN suggest is to simply change the value of the resistor marked "103" next to the pot; this is the feedback module's terminating resistor and by lowering it's value, more green output beam is needed to develop the same feedback signal. This is easier and better than shorting out any parts; if you have access to SMT devices anyway. I would leave the 103 resistor in place and piggyback a 472 or another 103 on top of it. This will extend the range of the pot by about 3x (472) or 2x (103), while retaining the APC operation.

I haven't tried it myself, but it is technically sound - and should work perfectly. I suppose you could "borrow" a 103 resistor from your module with the dead LD, and solder it onto another PCB, to prove this modification out.

Be sure to back the pot down before powering up, as the LD current will then be somewhat higher and I don't want anyone to kill their pointer! And always be sure to actually monitor the green beam when tweaking, and/or tune just below the point where the LD current starts to "run away".

 

[deezdrama05]

Thanks corona- you are a life saver if this works!!! I may order some surface mount resistors online. What size do I need 1206's? and what value ohm resistors should I order? Is there a certain ohm value resistor you would suggest using if I remove the 103 completely and use one resistor?

 

[Corona]

1206s resistors are really big parts (for SMT, LOL), I think these are 0805 size (I don't think they are 0603, thank God). Since they are so cheap, I would order both 4.7k (472) and 3.3k (332). I would think the 4.7k would suffice, but as I can't test it, it's up to you to determine what works best / gives the appropriate range of adjustment.

Good luck, I can't wait to hear of your results...

 

[deezdrama05]

I cant wait to try it, the reason I asked is because lasermod said they where 1206 smt. I will order some and in the meantime try to use a couple from an old video card or something. So with the 472 or 332 do I want to piggyback on the 103 or completelly replace it?

 

[Corona]

Completely replace it with one of those values, or piggyback it with another 103. IMO it is easier to piggyback another, makes the rework much easier

 

[deezdrama05]

ok, when you read resistors the last digit is the number of zero's to add right? so a 103 would be a 10k (10,000) ohm resistor? Is this right?

 

[deezdrama05]

I dont understand.....
If I piggyback 103 with a 103 that = 20,000 ohms of resistance
if I remove 103 and use 472 or 332 that = 4,700 or 3,300 ohms of resistance
so If I remove 103 and use a single resistor wouldnt I want to use a 203 which would be 20,000 ohms of resistance just like piggybacking the 103????
If not please work with me as im no electronics expert.

 

[deezdrama05]

Im trying to understand what piggybacking 2 resistors is doing. Does it double the resistance for example piggybacking 2 103's =20,000 ohms.
or
By piggy backing its actually letting more current flow through since theres now two routes for it to travel for example 2 103's = 5,000 ohms? I guess the latter makes more sense.

 

[deezdrama05]

Well I tried this mod but cant come to a conclusion based on a snag I hit. I took a 110 that I did the previous mod on, I desoldered the bridges and soldered the cap back on, Unfortunatley I lost the original 200 ohm resistor and could not find another one on any of the junk circuit boards I had. I ended up using a 100ohm resistor and then piggybacked the 103 but the beam was unstable and always settled back at around 5 mw. When removing the piggybacked 103's to try a single 3.3k ohm resistor A trace fell off. Nothing good is happening for me with these 110 units. Im now scared to sacrifice another unit to a mod since I have 3 dead 110 pointers laying on my desk. For one I need a smaller soldering tip for my 15w iron. If anyone else trys this mod please let me know the end result. And corona if you have any further info or suggestions im all ears.