Hi,

I put my Meggy Jr. together and put batteries in it. I played it for a bit before all the LEDs turned blue and the yellow lights on top flashed. I then realized that I had forgotten to install transistor Q8 as well as Resistor R3. The built-in game had actually been tuning fine though, except there was no sound.

I soldered the missing components in and now the Meggy doesn't turn on at all. I checked the voltage with a multimeter and I'm getting 5V at the battery, as well as at pin 1 of U1. I checked all my solder connections and they all look clean and shiny, no missing or extra blobs of solder that I can see.

Is it possible I damaged something by running it without Q8 and R3? Any other ideas about what I can try to fix it?

Thanks.

I put my Meggy Jr. together and put batteries in it. I played it for a bit before all the LEDs turned blue and the yellow lights on top flashed.

Are you saying that this was the failure mode-- that *all* of the 64 pixels turned on steady blue and the 8 LEDs up top turned on? Not one that I've heard before.

I had forgotten to install transistor Q8 as well as Resistor R3.

All that it will do is disable the speaker. No harm in not installing those, or in installing them later.

I'm getting 5V at the battery

WHOA. That sounds dangerous as heck-- disconnect it NOW and don't reconnect it until you understand what's gone wrong. If you're running from a 5 V power supply, you should not have a connection from that 5 V to your battery.

OK, I'm not an expert with the multimeter but I think I'm reading it correctly. I don't have an AC adapter, I just have three fresh AAA batteries in the battery holder and it is soldered to the board per the instructions.

When I test the batteries individually they register about 1.700 each. When I change the range on the multimeter to 20V DC, and touch the black and red probes to the black and red wires where they are soldered onto the board, I get readings of about 5.00. Should that not be happening?

The jumper is installed correctly, bridging the first two pins for battery usage.

I'm actually glad this happened because I am doing this project with about ten high schoolers this week and I need to come up with some procedures for troubleshooting dead Meggy units with the multimeter. I've made three of these and this is the first time is has happened.

So I'm looking forward to any ideas you might have. :-) thank you!

> I don't have an AC adapter, I just have three fresh AAA batteries in the battery holder and it is soldered to the board per the instructions.

Oh-- then I apologize for the bad assumption. Normally 5 V only shows up on the board when there's an AC adapter. And if so, it's very bad if that somehow gets shorted to the battery connections.

>When I test the batteries individually they register about 1.700 each.

That's quite high; I've never seen anything like it. 1.6 is typical for a brand new alkaline. What's the chemistry?


One thing that you might try right away is reprogramming the Meggy in the normal way. If it can be programmed, then the CPU is up and running. If not, then then check all the power and ground pins of the '328, being careful to check at the "knees" of the chip itself, not on the bottom of the board. Also check the soldering at the crystal and its capacitors.

Ok, I think I fixed it. When I connected it up to a laptop I was able to send it a sketch. But what was happening was that every five to ten seconds it would reset itself and start over.

So I went back and re-soldered the connections to the crystal. That didn't fix it. Then I tried re-soldering the connections to the reset switch, and that did it. Whew!

Thanks for your advice. It helped me solve the problem!

I don't know how to do the next step, though, and I wonder if you could give me more information. If I hadn't been able to upload a sketch, you said I could check the ground and power pins of the ATMega328 using a multimeter. How would I do that?

I downloaded the data sheet so I can see which are the ground pins and the VCC pins, but where would I touch the red/black probes?

Again, problem solved, and I am grateful for your help. Now at least I have some idea of how to start troubleshooting the kids' projects next week. (fingers crossed)

So I went back and re-soldered the connections to the crystal. That didn't fix it. Then I tried re-soldering the connections to the reset switch, and that did it. Whew!

A little surprising if you were seeing 5 V at pin 1. The reset switch is connected to pin 1. All that the switch does is connect that pin to ground. So, if it wasn't connected right, that shouldn't be causing a problem. Could be that the case was holding the reset button down, maybe?

I don't know how to do the next step, though, and I wonder if you could give me more information. If I hadn't been able to upload a sketch, you said I could check the ground and power pins of the ATMega328 using a multimeter. How would I do that?

I downloaded the data sheet so I can see which are the ground pins and the VCC pins, but where would I touch the red/black probes?

Keep the black probe on a "ground" pin, such as the negative battery terminal, or the "blk" pin of the USB-TTL connector (J2). Then, use the red probe to poke around and try out different pins. The pins connected to Vcc should be connected to the positive end of the battery (4.5 V), and those connected to ground should read zero volts versus the black probe.

Ok, I did this project with my students and out of ten students, two have problems (no display) and eight work fine.

What I am noticing on both of the non-working units is that I am getting a positive reading on the multimeter when I test pin 2 of the ATMega328. In fact, I am reading 4.5V on each of the first seven pins. When I test a working unit, I get a zero reading on pin 2.

Is this the issue, and if so, do you have any advice on how I might go about fixing it?

Thanks,

--Doug.

Ok, I did this project with my students and out of ten students, two have problems (no display) and eight work fine.

Can you please be more specific? Do you mean that they are not working *at all* or that they are working *except* for the display?

Besides the display, there's also the 8 aux LEDs, the speaker, and the programming interface. If any of those are working properly, then the '328 is operating correctly, and the problem is elsewhere. If none of them are working, it is most likely that the '328 is not operating correctly. Be sure and check with the handles off, so that you know that the buttons aren't causing any issues. Try reprogramming the Meggy to see if it will talk to you.

In either case, 90% of problems like these come down to one of very two basic problems:

1. A poor solder connection somewhere: maybe on one of the pins of the chip, or the oscillator, or possibly a solder bridge between two things that shouldn't be connected. You've had more experience soldering, so check all those connections very carefully for your students.

2. A missing or backwards component somewhere. Lift off the LED matrix and check the orientation of things under there, too.

In fact, I am reading 4.5V on each of the first seven pins. When I test a working unit, I get a zero reading on pin 2.

That sounds like the '328 may not be operating-- those sound like symptoms, not causes.

Thanks so much for the suggestions. They are helpful.

Over lunch, I went back and re-soldered all the connections on the 328, and the LED display pins, even the ones that looked fine to me. When I hooked it up and turned it on, the unit functioned normally. So I went back and did the same for Unit A, and now that one works too. Thanks again.

For posterity's sake, here is the weirdness that occurred:

Unit A never displayed the opening game (Attack) and gave no sign of operating at all -- no speaker, no display. Unit B displayed a purple screen where all of the LEDs were purple, and the yellow LEDs were all unusually bright. Sounds of the game were normal and reacted to button presses. When the board was flexed slightly, the game appeared as normal.