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FrozenGate by Avery

Capacitor is messing things up

pocketfluff

pocketfluff

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Oct 25, 2007
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I just got some amc7135's from dx and they are working well, output in the 300+ ma. For some reason, the capacitor across the diode causes nothing to flow. If i desolder it, diode shines (yeh kinda risky without cap but using 2 AA to drive :-/), put it back and the circuit seems dead.

Anyone have this problem or know how to fix it? I was under the impression that these boards were add a cap and go for open cans.
 





Have you tried a different capacitor? It isn't unknown for new components to fail.
I know this is a sucking eggs one but are you sure you got the polarity correct?

Start with the easy stuff, if it fails try something else ;)

Regards rog8811
 
Okies, I tested the cap, was fine. I also tried another similar cap, a bipolar one, and a ceramic one with all the same problem.

But I fixed SOMETHING ;D. Instead of soldering the cap to the wires coming off my diode, I soldered it to the inputs, so the rings on the bottom of the board. Works fine now, dunno why though :o
 
I am having the same trouble with my 7135's, I have talked with Gazoo and He has older boards that work with the cap on the output side of the circuit. I think that there has been some change in the boards, supplier, parts or something. I hope that Gazoo responds on this, his insight will prove to be quite helpful I am sure. Mine work with the cap on the input side also, I just wonder how much protection they provide to the diode there ? Catmandoo
 
Catmandoo said:
Mine work with the cap on the input side also, I just wonder how much protection they provide to the diode there ? Catmandoo
Click to expand...

Good to know that this problem isn't just on me. I hope somebody could shed some light about whether the cap has the same effect at the input or output, hopefully its the same.

Cat are your boards the one with holes evenly spaced along the outside or the ones in the pic at dx?

Btw, the price for the boards has gone up :P
 
Ok, looked at my boards, six holes in the negative ring, three together 180 degrees apart from the other three. Now here's the deal, I got three from Gazoo, bless His evil little heart, that are different from mine, ours ? , one came wired up, cap and resistor at the diode and works quite well. Inspection has shown that the working boards have the following #'s on the black chip on the board, 7135 with 38b below that. The chips on all my boards read L7135 with 0705 below that, these boards don't like the cap on the downstream side.
You'r holes might be a clue but what are you'r #'s ?   8-)
 
Don't want to upset the spam filter but Laser spamfilter Enthusiast spamfilter dot spamfilter com has a thread that I started about this subject in the need help section. If you get a chance check it out and see if it's not the same thing that you have going on. Catmandoo
 
I just read your topic on LE, looks to be the same problem. My boards are the same as yours with L7135 and 705 on the regulator. On the back mine says nanjg10.

While fiddling around, I suddenly found myself unable to get the adjustable output working again. This is with a resistor in parallel with the diode. Fix one problem and another one pops up? If the resistance is too low, does the board detect it as a short and shut down? I'm thinking this because I can't measure current directly off the board, I get 0.
 
I think that they fry pretty easy, I've nuked half of mine trying to solve this riddle, not that much of a loss though if they won't do what we want. Yes some of mine worked with the cap or resistor but none worked with both and those that I tried to put a cap on the output shot craps. What do you think about the cap on the input side ? we're trying to prevent surges from the batteries, I don't think that the board is where the spikes come from. I would like to use these as an add a cap and run an open can solution. Cat
 
How have yours fried? I tried running a laser off 2 full liths and the output dropped and dropped but once it cooled down and i drove it with 1 lith it was fine.

I also fixed my troubles with the pot in parallel with the diode. It WAS the low resistance. As i turn the pot lower and lower, the board doesn't start up consistently. Sometimes it will do nothing, sometimes a reading will flash up for a brief moment then die down, but sometimes it will start up fine. The higher the resistance (more current to diode) the better chance it has of starting up. At about 190-200ma, its pretty much 100% Isn't that perplexing? :-?

About the cap, i think its fine on the input side, I can't think of any particular reason why it wouldn't work.
 
I am befuddled by all of this. I just don't understand why the capacitor is causing problems with the 7135 at the output side.

Catmandoo,
I tested the output of the 7135's you sent be and got a zero reading....they were dead. The output voltage should be the same is the input voltage so I don't understand how any of your boards worked without the capacitor...lol We have discussed this at great length and the capacitor will have no effect on the output as long as the polarity is correct.

pocketfluff,
The only resistors I have used are 33ohm 1/2 watt. If you use a resistor with a lower value then it will need to be capable of handling more wattage. It also depends on the laser diode you are using. All I can say for sure is the SenKat diodes with the 33 ohm resistor in parallel are a good combination. I know the diode is getting about 250ma's and the resistor is absorbing about 100ma's. The quickest way to destroy the 7135 is by applying too much voltage to it. 4.5 volts is the maximum as far as I am concerned. Any voltage between 3.2 volts and 4.5 volts will result in the regulator maintaining a constant 350ma's output.
 
I switched out my problem board and gave it to my open can because it had an unusually high output of about 370ma.

The board i am testing my pot on now seems to be working well ^^.

Gazoo, will a pot at the board's input have the same smoothing effect as one on the output?
 
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