Non-responsive Arduboy. Red light charge, but that's it [Solved]

That was the conclusion I was arriving at but I wanted to gather more evidence to support it. (edit: been an hour or so, charge is still stuck at same voltage - so yeah, I think the charge circuit is busted)

Where do we go from here? Is there a part I can swap out?

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The battery charge controller.

image

It’s an MCP73831, I’ve probably got a few floating around if you want I can send you one. But it’s really hard to replace a component with multiple pins if you’ve not done it before. Typically you’d want to use a heat gun but that will damage the OLED. It’s very similar repair to flipping the RGB LED which some users have attempted in the forum, so if you want to take it on take a look at that:

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Since you’re not salvaging the part and just want to replace it’s possible to use a large tip and big blob of solder and flick the part off the pcb. Or cut the pins and remove one by one.

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It could just be a bad/broken solder joint. You could try just adding some solder flux to the pins and reheat (reflow) the chip pins.

Edit:
You could try add some solder flux to the other parts of the charging circuit too. All parts (except the charging LED and current limiting resistor for it) are in the picture below:

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So I found this datasheet https://cdn.sparkfun.com/assets/learn_tutorials/6/9/5/MCP738312.pdf

image

Which makes me think the key pins are Vbat and Vdd

Connected to USB to charge I’m measuring:
Vdd 5.02V
Vbat 4V

But the battery (from the tabs) still measures 3.6V

Keeping in mind I have no idea of the actual circuit here…
image

  1. 3.6V (same as the battery reads)
  2. 0
  3. 0
  4. 4.9mv (millivolt!)
  5. 5.02V (my USB input voltage)
  6. 0

Can someone shed some light on the circuit here? Or where I should chase the voltage? It looks to me like the charge management controller is working fine, but somewhere between it and the battery something has come loose.

From Production Arduboy Schematic

Maybe there is a problem with R7, if all the solder joints look in good condition you might also check the resistance of R7 to see that it is 2K ohms.

So I see R7 in the circuit diagram, but I’m not sure which of the two resistors in the picture from the Arduboy are R7 (since there is also R12).

Removing USB power from the Arduboy and measuring using resistance - I get…

0 between 1 and 2 in my picture above
252 kohm between 5 and 6 (but I’m not sure I’m reading my meter correctly as it is auto ranging)

So a bad resistor between 1 and 2? I have an autoranging meter… but I’m clearly not skilled in this area.

Those are actually the capacitors, you’d want to measure the black one between 3 and 4. You’re actually doing great don’t put yourself down.

The voltage at the VBAT terminal and the battery tabs should be the same. I kind of wonder if the solder joint there is bad.

LOL at myself.

Between 3 and 4 I measure 1.994 kOhm - so it looks right on.

Vbat in my diagram (upper left pin) is 3.99V - and battery (+) tab reads 3.6V

Where do I go looking for a bad joint? I’m mostly good with soldering - even SMD parts don’t scare me. http://lowtek.ca/roo/2011/surface-mount-soldering-repair-harmony-659/

That’s so weird. What ground reference are you using in both places?

I’m guessing on the back you are testing between the positive and negative terminals of the battery. Find a ground pad elsewhere in the schematic that sits after the battery protection and test with that ground.

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Well, I had made the mistake you guessed at first – and I caught myself.

The most recent measurement was from

  • USB connector shield (gnd) to Vbatt => 3.99V
  • USB connector sheld (gnd) to battery (+) => 3.6V

I’m going to take my working Arduboy apart and do the same measurements to see what’s up here. (and I can do a simple connectivity test too)

It’s not a mistake actually it kind of indicates the problem may be the battery ground is disconnected from the circuit ground, which is what the battery protection circuit does.

Try doing a continuity test from battery ground to the usb ground, try doing it both polarities (flip the + and - probes). If you can also test the resistance, both polarities.

You can also do this same test between pins 2/3 and 6/7

I think you will find that if you “disable discharge protection” this should give continuity to this signal. You may not have it otherwise.

Can you take a good high res picture of all these components and we can inspect for any bad solder joints? Sometimes the jellybean parts go bad so it could just be the battery protection chip. That would explain why it turns on with the pins shorted it turns on… but not why it wouldn’t charge.

This is odd. According to the schematic the battery + terminal is connected to Vbatt so you should get the same voltages. Where did you measure Vbatt?

See my picture above

Connectivity (beep for connection):

  • red probe on USB gnd, black on battery (-): beep
  • black probe on USB gnd, red on battery (-): beep

Resistance:

  • red probe on USB gnd, black on battery (-): 0.2 ohm
  • black probe on USB gnd, red on battery (-): 0.2 ohm
  • reference red probe touching black probe: 0.2 ohm

For the tests against the following pins

I’ve assumed that the picture https://aws1.discourse-cdn.com/standard14/uploads/arduboy/original/2X/f/fc41a63e715c136241ea33ee3019ee3f8e799246.jpg has the pins labelled

Connectivity (with USB power applied)

  • red on 2, black on 3: (beep)
  • red on 3, black on 2: (beep)
  • red on 6, black on 7: (beep)
  • red on 7, black on 6: (beep)

Removing USB power didn’t make a connectivity difference.

Could someone confirm the pin outs for the MCP73831
image

I measured connectivity from what I have marked as Vbat (upper left) and battery (+) and there was nothing. BUT when I measured the upper middle pin and battery (+) I had a connection there. [which makes sense as Vss is supposed to connect to battery (-) and I have connectivity across battery (+) and battery (-)]

My quick attempt at getting some close up shots - I can repeat with some guidance on parts / areas we want to explore more.

Vdd on the MCP73831 does look a little funky

Part KD25 matches with MCP73831 according to this
From the datasheet:
MCP73831-2

Vbat looks like a bad solder joint as if it is floating on solder. I can imagine the connection breaking on dropping / shocks making a poor or no connection. The pin has to supply the charging current.

I can confirm that Vbat is bad joint.

I measured my ‘good’ Arduboy as a reference. Battery (+) and Vbat have connectivity.

Carefully probing on my ‘bad’ Arduboy, I can test the ‘pad’ under Vbat and have connectivity - but if I only touch the leg of the chip I don’t.

I’m going to dab a tiny bit of flux (yes, I have the right stuff for SMD repair) and maybe tin my iron a little and see if I can reflow that leg (I might do the Vss one too). Here goes nothing - tricky as I’m working basically at the limits of my vision.

I think I’ve done it!

After my (almost embarrassing) solder work, I now measure 4.00V across the battery (+) and battery (-) when it is charging via USB. Disconnect and measure the battery, 3.75V.

I need a much finer tip for my soldering iron for work like this - and a jeweler’s loupe, because at that level I was working pretty much by feel.

I’m going to put things back together and let it charge until the charge light goes out.

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