Fried ATMega?

I’ve just finished building the motherboard; power rails tested OK, inserted chips, powered up, rails still OK, but the LCD just shows a row of blocks on the top row (backlight on), and the LEDs don’t respond to button presses (they were all on bar LED 15 first boot, then all off after).

Seeing a 20MHz signal (not sure of the level - picked it up with a spectrum analyser) near the Xtal - so have I got a fried ATMega? I bought the chip with the board, so sadly I’ve no way of checking. Anything else to check?

Thanks, Theo.

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Check that the crystal is correctly soldered; and that the two caps near the crystal have the correct value (18pF).

All the connections around the Xtal bell out, and the caps at 22p (as per the Wiki BOM - is this too far off?)

But wait! What’s that sizzling I hear? Turns out cap’n moron here put the 4700u in backwards. Right - I’ll put another (less bulgy) cap in tomorrow.

I’m an actual moron - 8 years in pro audio service and that’s the first time I’ve done that…

What might I have cooked?

4.7uF backwards? Probably nothing… In any case, it shouldn’t prevent the control board to boot…

That’s good news at least - I’ll replace it and see where we are. Are there pins I can look at on the ATMega with a meter (no oscilloscope…) to diagnose further?

Oh, and thanks so much for getting back to me so quickly! :slight_smile:

No, there’s not much you can do with a meter :frowning:

Right - I’ve swapped out the 4700u and the Xtal - still no joy. If the ATMega is seeing 5V, reset is held high and it’s seeing a 20MHz signal (I can see it on a spectrum analyser), is there any reason apart from corrupt/absent firmware that it might not boot? Not quite sure where to go from here - should I get an ISP (AVRDragon, or is there a better option?), or can you guys swap the chip out for me?

You can send back the chip, I’ll check it.

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Hi, I have the same problem. i Bought a pre-build ambika and everything was working fine. I was playing around with some custome firmware mods and uploaded them via sd card. But on my last upload my ambika got bricked. On boot i will get “LCD just shows a row of blocks on the top row” and can’t update the firmware anymore. Cant get it into emergency upload mode but sometimes it will boot but i don’t get the update option under preferences and weird characters. Please help!IMG_2943