MOV near fuse smoking

[cvonk]

Battery inserted, no LCD, uController or ethernet.  OpenSprinkler v2.2u

• Resistance Vin to Gnd approx 126 Ohms
• Resistance Vcc to Gnd was in the kOhms

Couldn’t find any solder bridges with magnifying glasses.  Decided to move ahead.

• Vin was 5V
• Vcc was 3.3V

After approx 15 seconds, the metal oxide VAR (U0), near the fuse started smoking.  Color changed from blue, to blackish.

Please assist,

/c

AC from power brick is 28.25V unloaded (not attached to board)

 

 

 

[Ray]

Resistance Vin to Gnd approx 126 Ohms

This is an issue: the VIN to GND resistance is too low. The instructions clearly that ‘The resistance should be at least several kilo-ohms. If either resistance is below one kilo-ohm, there is probably a shorting or solder bridge somewhere.’

It’s going to be a bit tricky to find out the issue. But to start, I’d ask you to post pictures of the front and back of the PCB (without LCD), and either post them here or send to [email protected]. Take the pictures under good lighting conditions and high resolution. Thanks.

[sfyffe]

Pictures would be great if you could upload them.   Is cap C2 in backwards?

Stephen

 

[cvonk]

Thanks for your prompt replies.  I posted some picts at  *)

http://www.coertvonk.com/technology/embedded/opensprinkler-picts-10950

depending on the browser, you should be able to “save target as” to get the full resolution.

It is dark here, so pictures are with two flashes.

 

Aside, is there a png file for the board layout?  Would be helpful to have the silkscreen to verify component placement.

Thanks a zillion,

/c

*) The forum didn’t let me post with the full res picts attached.

 

[Ray]

The soldering quality is decent. After checking all the VIN traces, the only thing I can identify is the relay’s upper-middle pin (close to the top edge of the PCB), there seems to be a solder ball that touches the nearby trace. Normally this isn’t a problem, since the traces are all covered by solder mask, however, sometimes the very edge of the trace may have copper exposed, so if you have a solder ball touching it, this may lead to shorting. I suggest using your soldering iron to reflow the relay solder joints, and re-check the VIN-GND resistance. If you still can’t figure out, send an email to [email protected] and we can see what we can do to help.

[cvonk]

Ray, I see what you say about the relay based on the .jpg.  I cleaned up the flux, reflowed the relay connection, but still got a <1 kOhm between Vin-Gnd.  Got inspired and reflowed all the other connections.  Now the res is 4.56 kOhm between Vin-Gnd, and 2.07 MOhm for Vcc-Gnd.  I replaced the fuse.  Great to have that spare 😉  Would you suggest reinserting the same MOV and try again?

 

thx,

/c

[Ray]

Yes, 4.56kohm is about right. Here is my suggestion:
1) plug in a USB cable to the USB port, measure VIN-GND voltage and VCC-GND voltage, they should be about 5V and 3.3V respectively. The 5V may have some variations since USB power is often around 4.6 to 4.9V. So anything in that range should be fine.
2) if step 1) passes, then unplug USB, go ahead and plug in your sprinkler transformer to the orange terminal and test voltage again.

The reason I would suggest step 1 in your case is to make sure everything from the 5V to 3.3V conversion is working fine. Because USB power is internally protected, you don’t have to worry about burning anything. Once that voltage test passes, if something goes wrong in step 2, then it must be a problem with the 24V AC to 5V conversion. So this can help isolate the problem.

[cvonk]

Power from USB went OK.  Connecting the 24 Vac, gives me rails at 3.29 and 5.10 V, and a soft click of the relay.

Besides your help, I can only contribute this to re-flowing the joints while wearing an old binocular magnifying visor.  Ready to move ahead.

Thanks.

/c

[Ray]

OK, assuming you mean VIN-GND is 5.1V and VCC-GND is 3.29V, the voltage reading is correct. So you can go ahead.

[cvonk]

Up and running.  Smooth sailing from here.

/c

FYI button B1 and B2 might be reversed.  The middle button gives the IP address .  Holding the middle button during power up does the factory reset.

[Ray]

Good to hear that it’s finally working.

As to buttons: this depends on which firmware your controller is currently running. Firmware 2.1.0 uses B1 to display OpenSprinkler’s IP, B2 to display router’s IP; pressing B1 during power-on goes to factory reset, pressing B2 during power-on does nothing. Prior to firmware 2.1.0, pressing B1 during power-on goes to self-test, pressing B2 during power-on goes to factory reset.

[Author]

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