Repairing rare paintball gun circuit board?

[eskoskimo]

Maybe in in over my head for a first post lol.  I have limited experience with arduino, messing around with beginners 555 timer kits and bread boards, and have plenty of experience soldering from working with RC hobby stuff.

Want to try repairing a rare circuit board for one of my paintball guns.  It functions flawlessly except for a constant current draw, even when powered off so it will drain a 9v in about a week to the point where the gun powers up, but will not longer fire correctly. I have another identical gun that works fine and the battery will last seemingly indefinitely if not used.

I have isolated the board from grounding on the gun frame, and all other electrical components so I know its somewhere on the board.
I recognize what most of the components are, just really not sure where the logical place to start desoldering components for testing/replacement.

Here's a link to an identical board that i'm considering fixing, it fits and EGO8/Sl8R paintball gun  http://www.pbnation.com/showthread.php?t=3928481

thanks for any help or guidance peoples!

[Vgkid]

Is it part of a e- trigger, or electronic hopper. Sounds like there could either be an issue with its sleep mode, or a display drawing tomuch current( if there is a issue with the sleep function). What batteries are you using, and what are the results of others using that board?

[eskoskimo]

Its the e-trigger gun board, running on 9V battery.  When you turn it off, it draws a very small amount of current, just enough to be a problem.  The other gun, and that board placed in the problem gun I have runs prefect in the gun, zero current draw and powered off.  Both boards were tested with an amp meter to verify suspicions.

Already talked to the manufacture about possible repair, or reflashing it and thats not an option anymore.

[digsys]

Well, you've started off good, with the comparison idea. Unfortunately, now you're stuck with component level tracing. Start with comparing voltages
(after the power down period SHOULD be up). If that doesn't help, start removing components, start with DC caps, LCD power etc.
I don't think there's a simple solution. You can also SWAP parts with the "good" unit.

[Blastcap]

I miss my Sl8R, godspeed with your repair.

[eskoskimo]

I had never even considered the LCD screen, that one would be tricky to remove if I ended up going down that road.   I have been trying to learn as much as I can about zero power draw circuits so caps kinda makes sense to me though.

Either way I'm definitely not swapping parts with the good board, dont have that much faith in my abilities just yet lol.

[digsys]

Another method we used in the old days when test tools were limited - make up a voltage / current probe "head", with 2 very sharp pins a few mm from each other -
some people clamped pins in a piece of wood. Then on VOLTAGE range, you can actually trace down which Vcc track it is heading, even right up to the "bad" part.
With the low currents you're talking about, you'll need a high resolution voltage scale. Basically, you're following the Voltage drop along the tracks.

[eskoskimo]

So with the 2 pins spaced closely like that you hook up the positive, and negative leads the pins, like super tiny probes?  Then measuring the voltage between them, and follow the path to the problem kinda idea?

Sounds tedious but i like it, something that might actually provide some information i can see before I dive in to soldering.

[digsys]

So with the 2 pins spaced closely like that you hook up the positive, and negative leads the pins, like super tiny probes?  Then measuring the voltage between them, and follow the path to the problem kinda idea?
Sounds tedious but i like it, something that might actually provide some information i can see before I dive in to soldering. 

NOT tedious at all, and actually quite FAST. You literally just probe along the power lines, and when the current takes a turn, you know instantly.
The idea is that the pins are thin and sharp, so easily puncture the csolder mask, with no damage.
Admittedly, circuits drew a lot more power in the TTL days, but with a sensitive enough VM, it MAY be still possible.
A quick pre-test is to probe the VM between power pins of all devices connected to Vcc. Just compare the voltage drops, some +ve, some -ve.
You then get an idea of where the current is going. ie Between Vcc pins

[Ian.M]

If its taking a week to drain a PP3, then the leakage current is under 4mA (3.57mA for one week is 600mAh.  It looks like the board has 10mil or 16mil traces, which are 19 or 12 milliOhms/cm respectively in 1 oz copper, so at best you'd be getting around 70uV/cm along the trace that's got the excess standby current.  Thermal EMFs  are a real problem when you are trying to measure uV so even if you've got a great bench meter that can resolve down to 1uV, probing along the power lines is unlikely to work well, if at all.

Unfortunately high standby current is typical of MCUs that have suffered ESD damage to an I/O pin that hasn't quite killed it.  If that's the case, unless you have the full firmware image, a spare MCU and the correct hardware tool to flash it, you are FUBARed.

[digsys]

If its taking a week to drain a PP3, then the leakage current is under 4mA (3.57mA for one week is 600mAh.  It looks like the board has 10mil or 16mil traces,
which are 19 or 12 milliOhms/cm respectively in 1 oz copper, so at best you'd be getting around 70uV/cm along the trace that's got the excess standby current
.... you are FUBARed. 

Yes for sure, but the OP has limited options, unless he starts desoldering and/or swapping. Maybe he can get some ideas using options listed.

[eskoskimo]

Huh, well then lol.  Sounding more like I might just leave this thing alone and start learning about arduino so maybe I can replace it when if finally dies completely.