I recently added 11 extra AMC7135 chips to the driver of my Shadow SL3, and since doing the mod, the light flickers intermittently on low and medium modes, and even when switched off. It works perfectly on high mode though.
Using a DMM, should i have continuity between the GND and OUT pins?
Cheers
Matt
EDIT: Here’s the SL3 driver before the mod
I don’t know the answer to your question, sorry,
but I would like to see that driver after modding 
I'm no expert, but there should be no direct connection, but I think I usually see a continuity with resistance between those paths on a typical 7135 based driver board. I got a cheap DMM I'll use for continuity tests and I believe it beeps when I'm doing those cross-over tests, but then checking the value it reads, it's not at 0001 that a direct connect would give, but the value is way up there. Guess it depends on the trigger level in your meter.
I haven seen what you are describing, but if you are getting flickering with power off, it may be unrelated to the 7135 mods you made. If the switch disconnects the battery "-", then there's something flaky in the switch, but if it's an electronic switch, then maybe something on the driver. Typically, low and medium modes are done by PWM (high frequency of ON/OFF cycles), so seems like something in the power turn on/off area that's flaky. I'd carefully check through the entire driver, wires leads causing inadvertent contact, mount points/surfaces, possible solder splashes, etc.
sounds like it’s either a flaky switch as Tom said or you’ve got a dodgy connection on one or more of the Vdd pins, which are used to switch the chips on an off (PWM) for low and medium modes.
Thanks for the replays. what’s the vdd?
I’ll post a pic of the noises driver soon, but its not a great pic. Shows my not so great soldering too 
Here’s a pic of the modded driver
Maybe post closeups of both sides of the board for our experts to have a better look. It sure seemed like an obvious mod. Good luck.
I use a pocket 10x mag glass w/light to carefully inspect things - not sure if you did that, but I've spotted things needing cleanup with that glass I would have definitely missed. Also, clean up the flux as best you can from the board with 90%+ alcohol -- flux can cause issues.
Some of those chip legs newly soldered are a bit risky -- I shouldn't be criticizing (
), but look those over very carefully for the slightest little crossover. The back ground legs should be soldered too - helps with the heat path.
Yeah, the soldering didn’t go too well, but I made sure I didn’t bridge anything, and checked with a magnifying glass. I soldered the rear gnd pins too.
Cheers
Matt
the Vdd pin is the one on the right, when you have the 3 pins pointing down. It’s used to “gate” the chip, so current only flows to ground when a threshold voltage (3V?) is applied to that pin. Any current less than full drive is achieved by having the MCU pulse the Vdd pin with its threshold voltage, essentially turning the chip on and off very fast.
As you’re not having problems on high, it’s unlikely to be a heat problem. Does the switch physically disconnect (no current to driver when off) or not? If not, then you could have a teeny tiny short somewhere between +ve from the battery and the Vdd line (shared by all the chips I believe, unless the LEDs are powered by separate banks of chips). That might provide just enough intermittent voltage to switch the chips on erratically, but be too small to maintain the current without opening. No idea if that’s the case, mostly waving my hands around here 
As far as i know, all the chips are wired in parallel, so all the Led should be powered by the same bank.
The switch is electronic, so uses a small amount of power while the light is off, so maybe that is giving enough voltage to switch the chips?
I just cleaned the circuit board and checked for bad joints etc and couldn’t find anything. I then tested the light, it still flickered with the power off, but didn’t flicker on high or medium. It flickered on low, but only a bit, not like before.
One thing i mentioned earlier, the GND pin and OUT pin have continuity between them on the SL3 driver, but i tested a driver in a P60 that has 7135’s, and i don’t get continuity between the GNd and OUT pins on that driver.
Sounds like a bridge or solder splash - maybe somewhat hidden? Hhhmmm. Since all are in parallel, one bad bridge effects the whole thing -- interesting the flickering was reduced after what you did... Sometimes with solder joints really close, I'll lightly rub the area in between to clear flux using a tweezer, even though I can't see anything there. Not sure, wonder if heavy flux would have enough conductance to be a partial bridge.
Thanks for your help Yeah it’s strange. Ill do some more testing tomorrow. When i cleaned the circuit board, i dipped a cocktail stick in the cleaning solution and ran that between the pins etc on the board to get rid of flux and splashes etc.
I wonder if its possible to get hold of another SL3 driver so i can solder up another one and see how that behaves?
Or has anybody else decided to give it a go?
You may try to re-do the cleaning process all over again (yep a pain), and then maybe try the tweezer thing as a test. It seems like I always wind up scraping something off when I do that.
sounds like you’re getting there! I’d go for something mechanical as Tom suggested - you can even use an exacto knife, there aren’t any traces between those pins that I can see, so you don’t have to worry about cutting anything (even if you could, cutting traces is hard work).
no idea why GND and OUT should have continuity, that seems contrary to how those chips are supposed to work? Hopefully someone like PilotPTK could chime in, he’s forgotten more about electronics than I’ve ever known.
Yeah, getting there I hope. I re-tested it again, and its still flickering when off, flickering a bit, but acceptable for usage on low, and perfect on medium and high modes.
I’ll give it another clean and a scrape tomorrow and see how I get on.
Cheers
Matt
What kind of solder did you use? I’m interested in what kind of fllux-core it has. Did you use any additional flux? If so, what kind?
PPtk
P.S. how are you testing continuity between power and ground? Measure it using OHMS mode on your DMM and tell me that value. It’s likely that there’s just a resistor pull-up somewhere in the microcontroller circuit. I’ll bet the resistance between power and ground is many KiloOhms.
I’ll take a pic of the solder and flux and post it later.
I’m getting about 27 ohms between OUT and GND.
Edit: Could a faulty 7135 chip cause the problem I’m having?
Cheers
Matt
Unfortunately, that is what I am beginning to suspect. I have only ran across this problem once when adding a single 7135 to a board. It reduced the overall current, and replacing it with another 7135 solved the problem.
Ok, I think I’ll have to wait for a new soldering iron tip to arrive first before attempting removing anything.