Problem

[mnarel]

I tested the LED driver per Cpt Kirk and get a good 5V accross pins 13 and 14.   I tested the PIC at 27 and 28 again and get about 3.8V.   I tried to test PIN 1 on the PIC using pin 27 as the ground and I get about 3.0V not 3.3    Do I need to use another location as the ground for this test or is it possible I've found a potential problem area?

I basically took a mental health break from this board this afternoon and assembled one of the new boards (board 13) from the recent COOP.   Full functionality first try on that one so  I know I haven't lost my mind completely.  I'm now back on the problem child (board 12).  I'm going to lay the two boards side by side and do the ohm resistance tests from earlier on each with the PIC removed.   I'm not entirely confident of what the specific readings will mean, but if they differ between the two units I will note where I find it.  I'm doing this with power removed (obviously) as I don't want to go poking various things without quite knowing what I'm doing.  I can't believe shooting 120V AC through the LED driver on accident would do anything to help my cause here.

[CaptKirk]

I hope the 3.8 was a typo as that is very high for a 3.3 volt device.  3.0 does not sound right for pin 1 (but I am not measuring my working board).  Could you check that same Pin 1 voltage on one of your working boards?

[jess_her]

Pin 27 is 3.3v       pin 28 is ground                  pin 1 is reset         so when the  reset switch is pushed, pin 1 goes from 3.3v to 0 volts  

[RJ]

Pin 27 is 3.3v       pin 28 is ground                  pin 1 is reset         so when the  reset switch is pushed, pin 1 goes from 3.3v to 0 volts

No the pin#1 should be about 3v all the time.

RJ

[jess_her]

   I tested the PIC at 27 and 28 again and get about 3.8V.   I tried to test PIN 1 on the PIC using pin 27 as the ground and I get about 3.0V not 3.3    Do I need to use another location as the ground for this test or is it possible I've found a potential problem area?      Sorry about this mybe some day somebody can teasch me how to do quotes.

I beleave you have found the problem.    pin 27 is the power input and pin 1 is lets just for now call it a reset and it has nothing to do with the design of this board except for in board pic programing.   Both pin 1 and pin 27 should be 3.3 volts all the time. ( thank you RJ)     I think if you test this again using pin 1  plus side of your meter and pin 27 as your ground side of the meter then you should read about    -3.3 volts.     Some where  pin 1 and or the circuit board trace is shorted to or close to ground pulling pin 1 close to ground causing the pic into a reset condition and I beleave that this would cause all the symtoms your having.    

Now at the risk of passing on bad habaits  take pin 1 of your pic bend out the pin just enouth so when you reseat the pic it will be out side of the socket. your board should run now

[jess_her]

Real quick, circuit functioning properly measuring pin1 to pin 27 you should read o volts.   If this is all true then I think your short is under  the programing header plug. Pin 1 of the pic is tied to pin 1 of the programming header and pin two of the programing header is ground,  wow.   If I'm looking at the pictures correctly the trace goes from the programming header to pic pin 1. So the second place the short can be is under pic  socket at pin 1. Secont bad habit......   I have done this allot on acid damage board repairs. If you are very carefully pry up the plastic working slowly all the way around you can reveal the tops of the pins/ board. Clear the short and replace the plastic housing or solder in a new socket.

[mnarel]

Tried the "Pin 1 out" solution described by Jess_her without change in the result.  Board still acts the same under power with pin 1 removed from the socket.

[mnarel]

I have now also lain my freshly minted and functioning board 13 next to the problem child (board 12) and done a few meter tests on each with the following (disenheartening) results:

Board 12:  Pin 27-28   3.8V
Board 13:  Pin 27-28   3.8V

Board 12:  Pin 1-27  3.0V
Board 13:  Pin 1-27  3.0V

These appear to be functioning normally and suggest to me that the problem must lie elsewhere

All of these tests are being done on the top of the board, under power, with the PIC in place.  I am stabbing the socket/pin junction where the PIC prongs meet the socket.

[Dennis Cherry]

What do you mearsure on the output of the 3.3 volt regulator?

Sounds like you might have a bad regulator?

[mnarel]

Not sure where to stab to measure that. 

[jess_her]

Good morning,
Pin 27 on the pic is a power input to the pic so if pin 1 has 3.3 volts on it in normal operation then you would see 0 volts measuring from pin 1 to pin 27 on the pic.  Can you measure from pin 1 to pin 28 on the pic? do you get 3.3 Volts here? IF you get 0 volts here then somthing is wrong the pic is in reset.  
I really do believe your on the problem.


If you had it with this board I'll buy it from you at your cost, want a LE anyway.

Jess

[LondoB5]

If Jess's test turns out correct, then it probably doesn't sound like the pic or the pic socket is the issue...but other experts in this can correct me if I'm wrong.

Also if you reprogrammed the pic while it was on the board, then it couldn't be the pic or the socket as it probably would have returned an error.

RJ said in previous posts to check the display, as well as the tiny capacitor...don't have the board in front of me...I think it was 2700pf.
Although I'm not sure of a good way to check the cap other than desoldering and replacing with a new one...as I said, I'm no expert. Just trying to help.

[mnarel]

Here are the actual voltages taken across the PIC pins.

27 and 28 - 3.8 volts
27 and 1 - 3.0 volts
28 and 1 - 0 volts

Everyone is going to have to excuse my lack of knowledge of DC based electrontics, but when you ask what the voltage on a pin is  (ie  What's the voltage at pin 1, or what's the voltage at the 3.3v regulator) I don't know how to test for that.  I need two places to stab the meter.   If it was a normal AC 120v circuit I'd stab the neutral bar... I figure if I do that here, I'll fry whatever I'm trying to test.  I'm more than ready to post any readings anyone can think of that may help, but in all cases assume I'm an idiot and give me a place to stab each probe.   

I'm ready to start removing and replacing components at this point... I have 3 more complete sets to assemble on hand, but obviously I don't want to try and desolder a 28 pin socket at random, so if we can narrow it down with some confidence I'll crank up the desoldering equipment.

Jess_her -  I hate giving up on something so I'm not ready to throw in the towel just yet, and I need 14 functional Lynx expresses for my display (which means I want 15 on hand for the season).  At present I only have 14 including the problem board, so I also want to make sure I can replace it before giving it away.    On the other hand... too many more days of this and I'll probably be ready to give it up at a heck of a discout

[jess_her]

let me do some more research  going on vacation tomorrow bee back next sunday

[LondoB5]

I'd replace the cap first, then if that doesn't work, the LED display.

If the pic worked in one of the other boards, then it's not the pic itself.