Troubleshooting a fried board

I soldered the 5V Molex the wrong way around on my Gen7 1.2 and burned a finger on the ATMega getting 12V…

I no longer can connect to it over serial / USB, so obviously I've fried something — how can I check if it's the ATMega or/and other components that I've blown? Which are the likely candidates? Can the right or left LEDs give an indication of what needs replacing?

Also, when I at first tried with the ATX20 and the Molex connected, and had the jumper set to ATX20, the lower right LED blinked once. Is this normal behaviour or a result of my unorthodox power 12V power istallation? (No other LED was lit, and I couldn't connect to the board)

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I soldered the 5V Molex the wrong way around on my Gen7 1.2 and burned a finger on the ATMega getting 12V…

That's why there are instructions to measure voltages _before_ inserting expensive chips. *sigh*

So you created a short between 5V and 12V. Apparently you have an "always on" PSU, which doesn't use the software on/off feature. That short blink of the LED was the time between turning the PSU on and the PSU turning off due to overload. PSUs have fuses inside which regenerate after some time.

All you can do is to start the same way you should with a freshly soldered board. Look for burnt traces, then measure voltages, then try what works.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Yup, should have measured before installing components, but didn't have the PSU and what can possibly go wrong?

Oh well, I'm measuring the components one at a time and nothing looks burned or smells funny. The PSU gives power when I short green+ground on the ATX20 connector, is that what you mean by "always on" ?

Silver lining is that I have a spare ATMega and know how to bootload it now — had I gotten one from you and killed it this would have been even more depressing…

... i think your ATMega is fried, as 12Volts even for a short time is a killer - especially if you noticed excessive heat!

For the other components you can check if the devices have maximum voltage ratings - if you overlasted the max. ratings of active electronic components by some volts or overheated them for some seconds, then i'll replace them too ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

With the Molex resoldered I did the measurements as they're listed here [reprap.org] with just the Molex conected and I get all the correct values — would this indicate that the components are ok or can there be "wear" which only shows up after a while? (I've always thought of electronics as "either working or not")

The caps don't bulge, but should I exchange anything just in case? I've measured the diodes and the the mosfets, and they give me the same value as the spares I have, so perhaps they're ok? (I'll exchange the ATMega of course)

Edited 1 time(s). Last edit at 08/03/2011 04:03AM by monocultured.

... the diodes should be OK, caps are mostly specified for higher voltages than 12V (or chek if you have some with lower specs).

The MOSFETS could be OK too if you haven't driven them.

But IC's are problematic - here you can even have a working device which will break down after a while, so better replace them ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Apologies for being daft, but apart from the ATMega, which ICs do you mean? The Pololu boards were plugged in but were cold to the touch and I'm thinking since they weren't driving the motors at the time there was no foul. Endstops not plugged in at all.

... you have to check all IC's and other active devices connected to the 5V line for their max. specs.

Many IC's and TTL- or logic inputs driven normally with 5V are specified to 7V max. or lower. So even a short exposure to 12V could damage or wear them, regardless iff they were driving or not.

You can be lucky, and they will work, but 12V on 5V-inputs is a typical IC-killer ...

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

For anyone else looking for how to test Pololus, I opened up a thread over at their site and got some suggestions: [forum.pololu.com]