AP-16 board broken?

[ConceptShed]

Hi
Today for an unknown reason, while doing some wiring up of an AP-16 board that was working fine yesterday, my board has stopped working.
The symptoms are that it doesn't respond to any of the aux inputs being connected.
There doesn't seem to be an increase in noise when I turn up the volume.
The 2 LEDs located next to the pins of the 2 voltage regulators are cnstantly on.
The status LED does not come on at all.
Also I noticed that the 74hc165 has burnt out halfway along.



Could this chip be the source of my issues? If so, what is the part number so I can get a new one. Cheers

[JonnyMac]

It's not likely that changing the 74HC165 will fix the board; I suspect bigger issues.  What was applied to the AUX inputs that caused this?  My fear is that I high voltage applied to the AUX pins destroyed the '165 and then made its way right to the Propeller processor.

It would be best to return it to us for repair.  If that's not possible (or practical; are you not in England?) then I would suggest having a qualified technician remove the '165 and retest the board functions then. If everything else returns to normal then you can replace the chip and move forward, otherwise you really should send it back to our TN office.

[ConceptShed]

Thanks for the reply. That's a shame that it might have fried the MCU. I don't think it was connected to a higher voltage but my colleague said a spark came out when he touched it against the header marked with an arrow down.

It is true that we're in England so if you could talk me through the repair, it would be easiest. I've done a bit of SMD retouch work so I should be able to swap over the SOIC chip. Once I've replaced it, what tests can I carry out to check whether its functioning OK or not? We've got a 2 channel oscillascope but no logic analyser.

Also when I search for 74HC165 I get results for shift registers, and inverting and non inverting buffers. Which is this one exactly?
Many thanks

[JonnyMac]

I would suggest removing the '165 and then testing the board (other than AUX inputs).  It's possible that the bad '165 is leading to the other problems you're seeing.  If removing it removes those problems then you can drop on a new '165 (which is a shift register; sadly, a lot of folks creating web pages for parts have no idea what the part is....).

I would also suggest reloading the firmware in the event the voltage issue caused a corruption of the program.

[JackMan]

I don't think it was connected to a higher voltage but my colleague said a spark came out when he touched it against the header marked with an arrow down.

Just wondering what exactly got "touched" to the "arrow down" terminal.  I believe that terminal is a ground.

[bsnut]

I am wondering what voltage was connected on the Aux terminal strip. Did you connect voltage higher than 5vdc?

[ConceptShed]

Hi, There wasn't any voltage other than the 3.3V at the end of the strip that was connected. It was just connected via the NO and COM contacts of a microswitch. To be honest I am slightly baffled as to why it seems to have blown.
Anyway I'll try taking out the shift register and see how it looks

[bsnut]

Be careful when you remove the 74hc165 from the board so that the solder doesn't bridge the pads.

[ConceptShed]

OK so I got the chip off the board OK. I used a reflow hot air gun that we've got.
No luck on solving the issues though. The status LED still isn't responding, even after putting the latest firmware file 'ap16.pgm' onto the SD card.
It seems to be pulling about 200mA with pretty much no sound coming through the speaker, so I guess there's probably a short somewhere else.
I left it on for 30 seconds or so, and the propellor chip felt quite warm as well as the regulators.

[JonnyMac]

This is not good; you'll need to return it to us for repair.