TheBackShed.com

Forum Index : Microcontroller and PC projects : Explore 64 "no target found"

Author

Message

thirsty
Newbie

Joined: 22/06/2016
Location: Australia
Posts: 34

Posted: 04:29pm 28 Jul 2016

Copy link to clipboard

Print this post

So I've built an Explore64 but I can't get Pic32prog or my Pickit 3 to recognise.

I've got 3.3v on all the pins that should have that but because it's a blank chip I can't see if any of the output is correct.

I've looked at the OSC pins with my scope and they don't have a steady 20mhz on them. One has < 1mhz while the other varies a bit.

Not really knowing how this part works I thought I'd ask for any hints on where to look next. I've changed the xtal out along with the 22pf caps which didn't make much difference.

Any ideas?

mikeb

Senior Member

Joined: 10/04/2016
Location: Australia
Posts: 174

Posted: 04:48pm 28 Jul 2016

Copy link to clipboard

Print this post

1) Double check component orientation first.

2) With a strong light, and magnification, look for solder bridges. Particularly on the PIC32 pins. There is no guarantee you will see them but worth a look.

3) Now comes the 'fun', and most likely, bit. Set your multimeter for continuity (hope it's got a beeper) and with sharp probes, and a steady hand, check for continuity between all adjacent pairs of pins on the PIC32. Bet 'ya' find some. If/when you do it's time to get out the liquid flux, solder wick and iron.

There are 10 kinds of people in the world.
Those that understand binary and those that don't.

robert.rozee
Guru

Joined: 31/12/2012
Location: New Zealand
Posts: 2434

Posted: 07:53pm 28 Jul 2016

Copy link to clipboard

Print this post

also look for unsoldered pins on the processor. a neat trick i employ is to drag a fine sewing needle at an angle along the rows of pins - you'll hear a different 'ringing' if the needle passes over an unsoldered pin.

cheers,
rob :-)

Grogster

Admin Group

Joined: 31/12/2012
Location: New Zealand
Posts: 9590

Posted: 09:19pm 28 Jul 2016

Copy link to clipboard

Print this post

Yes, as the others have said, really REALLY important to check that all the pins on the QFP are soldered.

It is exceptionally easy to miss one or two, or get a solder bridge.

Do you happen to have a microscope?
You kinda need one for 0.5mm work, to be sure there are no solder-bridges etc.

Assuming you DO have a scope, and everything looks OK, next thing to check is that the legs are indeed soldered down on the pads - just like the members above have said.

Sometimes, everything can look just fine on the scope, but you have a leg or two that is hovering JUST above the pad, and is not soldered to it, so not making contact, so the programmer moans about no target.

I speak from experience - this happened to me just the other day. Chip programmed fine, but I cound not make the SD card work no matter what, and after several looks through the scope and deciding it looked just fine, scratching my head some more, then I took the board and looked at it SIDEWAYS with the scope, and the first five or six pins were just ever so slightly above the pad, and not soldered to it.

This made the QFP look fine when looking down on it vertically, but no contact.

Needless to say, all boards I do are now checked visually in both vertical AND horizontal directions, and also a test code is run(once the chip is programmed) to confirm all the pins are actually connected. I stole that idea from WhiteWizzard - thanks.

Smoke makes things work. When the smoke gets out, it stops!

thirsty
Newbie

Joined: 22/06/2016
Location: Australia
Posts: 34

Posted: 10:36pm 28 Jul 2016

Copy link to clipboard

Print this post

Thanks for all the hints guys. I went back and ran a soldering iron over the pins and checked each one with a meter looking for shorts but also checking for contact with the pad for each leg.

I replaced the xtal and the the 2 22pf caps as the output from the xtal on my oscilloscope didn't look right.

None of that worked so I went over the board one more time looking for issues and found the problem - the 470r resistor that is in series with MCLR and the ICSP header looked OK but one end was missing the metal bit so the solder wasn't contacting properly. Replaced that and all good!

A question though - should I be able to put a scope on the xtal and see the 20Mhz wave with a brand new non programmed chip with power applied? Otherwise how could you check if the chip is OK?

Print this page

To reply to this topic, you need to log in.