Problem

[LondoB5]

I beleive I do have a multimeter lying around (I was an amatuer electrician in a former life... just have never applied it in instances less than 120V AC or wiring less than 14 gauge).  If someone can let me know where to stab and what equals a pass or fail reading, I can start working that.

There are no obvious front side shorts on any of the resistors but I can't really see the socket pins on the front end.  Is there a way to check this effectively without removing the sockets and redoing?

Without the board being powered up, you could check ohms of resistance. In theory, there should be negligible resistance between shorted socket pins and infiite resistance between ones that are not shorted (unless they are shorted intentionally by a PCB trace).

[Dennis Cherry]

This is a long shot from looking at your pictures and also trying to simulate your problem on a LE.

I think your reset switch is bad or in backwards.  Your last pictures of your solder side does not have the alignment pin in the hole.

If the reset switch is held down then powered up, nothing happens to the display as you described. So i think it is one or the other.

[CaptKirk]

To check voltages:

You need to set DC voltage reading on the meter.  If your meter is not autoranging put the meter on DC 20V (or something close above 3.3).

Looking at the top of the board with the logo on the board readable that puts pin 1 on the upper left corner of the PIC.  Place put your RED lead on the top right pin (28)  and the black lead on the pin just below that (pin 27) and it should read 3.3v powered up obviously.  PLEASE BE CAREFUL AROUND THE exposed 120V (as you know as an amature electrician)!!

If you want to test the meter, get a fresh 1.5V battery and see if it reads 1.5V when you put the red on the top of the battery (the end with the nub) and the black on the bottom.

[mnarel]

Ok,   I have 3.3V at pins 27  - 28 conducting the test described by the Captain  (Damn it Jim... I'm a visionary Christmas display artist... not an electrical engineer!)

That seems to rule out the bad reset switch  (which sucks... cause that sounded like a really good... and solvable... problem)

[tbone321]

Ok,   I have 3.3V at pins 27  - 28 conducting the test described by the Captain  (Damn it Jim... I'm a visionary Christmas display artist... not an electrical engineer!)

That seems to rule out the bad reset switch  (which sucks... cause that sounded like a really good... and solvable... problem)

Did you do the test that RJ suggested of holding down the reset switch and powering up the board

[mnarel]

I did conduct the reset test.   unplug board.  press and hold reset as I plug in board.  Maintain hold on reset button.   No change.  Release reset. No change. 

  I examined the reset switch closely.  The spring operates normally.  It stays in the 'up' or 'out' position when released, there is no visible or audible sign of damage to it, and I have verified that it is oriented properly with the plastic 'pin' on one end in the corresponding hole on the board.

Can anyone tell me where to test for 5V?   I checked voltage at the LED indicators and get about 2V at both the 3.3V and 5V light... I figure this is normal... just don't know what to stab looking for 5V and don't want to fry anything.

[LondoB5]

Unplug the board set your meter for continuity, and check for continuity between the lower right side of the reset switch and the lower left side when the reset is pushed (from the top of the board, not the underside).
 
While you're at it, perform a continuity test on the lower right post and the lower middle post of the select and mode switches. Check both for depressed and not depressed. (again from the top side of the board).

If your meter doesn't do continuity, then do resistance. There should be almost 0 resistance when there is a connection.

[mnarel]

For giggles I tried the resistance test suggested.  I unplugged the board, flipped it to the solder side and tested adjacent pins on the PIC all the way up one side and down the other.  I got varying readings from 0 Ohms to infinite resistance including 2 Ohms, 4 Ohms, 10 Ohms, and 18 Ohms.   I suspect the board circuitry and whatever magic is going on inside the PIC are affecting this to the point of it being unhelpful.

...sounded good to me in theroy though.

On the reset button:

I do not have continuity, but using the Ohm meter I tested the reset at the lower right and lower left.  In the 'rest' position I get infinite resistance, when depressed I get zero resistance

On both the mode and select switch using the center and right bottom posts I get zero resistance in the 'rest' position and infinite resistance when depressed.

[LondoB5]

The pic itself needed to be removed for that first test to work.
As for the test of the select and mode switches...my bad. It should have been lower middle and lower left (from the top of the board).

[mnarel]

Ok... something interesting to report:

I re-did the mode and select switch tests and got the expected results.   zero resistance when depreseed, infinite in 'rest' position.

I pulled the PIC and did the resistance accross the adjacent pins and got infinite resistance in all pairs except the following:

5 Ohms pins 23 - 22
8 Ohms pins 12 -13
0 Ohms pins 1 -2

Does that mean anything to anyone?

[mnarel]

Wait wait.... board was facing backwards:

infinite resistance pins 27- 28
8 Ohms pins 17-16
5 Ohms pins 7-8

probably not as interesting now... but still Greek to me.

[jess_her]

Ok pin 7 and 8 is 5 ohms   I would be very carefull here   even though the pic is out other things in the circuit can cause the  low resistance on the two pins.  Looking at a data sheet on the pic pin 8 is VSS or power to the chip 3.3 VDC  and pin 7 is a data line. personaly I don't like doing resistance (ohms) testing to many other things play into the results. power the board leave the pic out check voltages on the same two pins. if they are shorted then you will see 3.3 v on pin 7 . I would strongly urge you to compare your results with a known good board with the same setup (pic in or pic out). You have a very good map in you other boards.
Jess

[RJ]

Ok,   I have 3.3V at pins 27  - 28 conducting the test described by the Captain  (Damn it Jim... I'm a visionary Christmas display artist... not an electrical engineer!)

That seems to rule out the bad reset switch  (which sucks... cause that sounded like a really good... and solvable... problem)

If the pic has 3.3v on these pins you know power is good on 3.3 v

Now make sure that pin #1 on the pic is at 3.3v +  so it is no in reset.

Then we need to check the 5v section on the led setup.

I do not have the information with me as I am out of town but once I get back I can tell you where to check on the display chip.


RJ

[CaptKirk]

On the led driver (the big chip) pin 13 is ground (black lead on meter) and 14 is power.  Looking at the chip as it is oriented on the board (on its side), pin 1 is lower left, 13 is lower right and pin 14 just above it.  I think RJ is saying that should be 5v. The datasheet linked from Mouser says it should be 5v also...

[KeithTarpley]

Greetings,,,

You could also check with a known good unit and compare readings with this unit, side by side.

Keith