Finding a short on a prototype board

That might be an application for the fluxgate current probe discussed here a while ago.

The question (still unanswered) about inner layers remains.

Why purchase a bench supply ?

Google for LM317.

Then google for transformer, enclosure, capacitors, potentiometer, meter, fuse, line cord, heat sink, and machine shop.

Ok, found the problem.

I had to add the power pins to my symbol for the MCU. When adding the pins, got one VDD-VSS pair reversed! As the boss says, Wrong Way Charlie strikes again!

Now I have to see what I can do to fix this on these prototype. Can't waste $1200 to do a re-spin... :-(

Charlie

Blue wire ?:-) ...Jim Thompson

So the Vdd-Vss short is internal to the CPU chip?

You can probably just cut open both bad connections, if it's not a BGA; there are likely other pins that can do the job.

Your boss is being unkind.

Yep! have to lift the pins (Veerrry Carefully...) and then air-wire them to the correct places. Well, I have ten boards to try and get it right on... ;-)

Charlie

Well, she is the boss... ;-)

It is a PIC24FJ256TQFP. I already found a problem with the routing on one ground, don't want to lose another one. I always lift these pins unintentionally when I try to hand solder them. Lets see if I can do it when I want to!

Charlie

Techniques I've used:

1. Use a 0.5V, 10amp adjustable current supply. Voltage is low enough so it won't affect parts on the board. We have a Fluke TiS IR imager which allows us to locate the warm spot. Sometimes this works fine, other times not depending on the short.

1. Feed a few amps of current to the power plane and measure with a microvolt meter at various bypass capacitors around the board. By deduction, you can get close to the area. You may need to feed the current in various areas to figure out what area may be shorted.

If your pcb house messed up, you may have many shorts all over your board. If that's so, the above techniques won't work. I've come across these on rare occasions, one just recently.

If you're a hobbyist, and want to get away from the teevee set, it might make sense to build your own power supply. But for $70 or some such, a metered, finished bench supply doesn't make sense to build.

Ebay has lots of power supplies too...

I need benches - so need a supply of (for) them..

You forgot the most essential part..the elbow grease needed to put it all together.

LOL. I think I'll send a summer student to order a jar of that stuff from McMaster...

Did the first board, but it won't program. I think in all that high current testing I probably baked the processor. On to board 2...

Charlie

I've been real impressed with this...

So much so that I threw away a bunch of Heathkits of comparable rating.

But you can still get them via < James Knight >

Never heard of wireless power? :)

Jamie

Yep, AA, AAA, C, D,...

put it

For a few shekels more you can cut the ripple voltage by a factor of

-- Cheers, James Arthur

Yikes, a 90 watt metered bench supply for $50. That seems impossible.