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 0 of 9 LEDs working
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By: Anonymous: Eric S () on Wednesday, October 14 2009 @ 08:54 PM PDT (Read 10160 times)  
Anonymous: Eric S

Hey all.

First let me say that I make no claim to being experienced with putting electronics together. So pre-excuse my noobness.

My basic issue is that NONE of my LEDs are lighting up. I followed the instructions exactly and have compared the outcome to the pictures in the instructions. Everything looks like it's in the right place and orientation. All of the connections look ok. I even ran over them a second time just to make sure.

I pulled my tester out to see if I was getting voltage at various spots on the board. Across the capacitor I see 3+ volts. Across 9 of the pins on the MC I see .03 volts (I assume the 9 I found with .03 volts correspond to the 9 LEDs). The voltage across the switch varies from about .08 to about .18 with each click. If I test the path from one of the MC's .03 volts to the corresponding side of the resistor I see 0 volts. Across the + - on the LEDs I see .01 volts (which I'm taking to mean 0 volts).

So from my testing, it looks like I have current running out of the MC. The issue must be between the MC, resistors and LEDs, right? But all 9???

Any thoughts or help would be GREATLY appreciated. Thanks guys.





       
   
By: Windell (offline) on Wednesday, October 14 2009 @ 11:12 PM PDT  
Windell

>But all 9???

Yep, that probably indicates something systematic, rather than a bad joint here or there.

> Everything looks like it's in the right place and orientation.

And yet, things aren't working. That probably means that there is something with the wrong placing or orientation, or possibly a short circuit or a bum chip.

First make sure that the chip isn't getting *hot.* If it is, that probably means that it (or its power supply) is backwards. Then, important test: Check that pin 1 of the chip (that's the one with the square pad) is at about 2.7 V (not about 0 V) above ground-- the point with the black wire.

Let us know how that turns out, and we'll go from there.


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By: Anonymous: EricS () on Thursday, October 15 2009 @ 07:40 AM PDT  
Anonymous: EricS

Thanks for the tips Windell.

The chip is not hot at all, not even warm.

I wasn't sure which pin was #1. You said something about a "square pad" but I don't see that unless you were trying to describe the chip itself.

A) I'm assuming it's one of the corners. I noticed that one corner of the chip has a small circle (upper right if the semi-circle edge is pointing right). From this pin to ground I see nearly 1 volt (.97).

Cool My next best guess would be the pin that connect to the capacitor (bottom right if the semi-circle edge is pointing right). Running that to ground reads half a volt, .47.

I went through all of the other pins and didn't find any readings higher than .1 volt.

Additionally, if I put my tester across the the capacitor and the pin I mentioned in step B above, I see 2.4 volts.

Does this tell you any more?

Thanks in advance.





       
   
By: Anonymous: EricS () on Thursday, October 15 2009 @ 07:57 AM PDT  
Anonymous: EricS

Here are some pics. I don't know if this really helps, but it kind of shows the orientation of the components and the soldering. Sorry about the blurry-ness.






       
   
By: Windell (offline) on Thursday, October 15 2009 @ 10:00 AM PDT  
Windell

I wasn't sure which pin was #1. You said something about a "square pad" but I don't see that unless you were trying to describe the chip itself.

A) I'm assuming it's one of the corners. I noticed that one corner of the chip has a small circle (upper right if the semi-circle edge is pointing right). From this pin to ground I see nearly 1 volt (.97).


My next best guess would be the pin that connect to the capacitor (bottom right if the semi-circle edge is pointing right). Running that to ground reads half a volt, .47.



On the bottom side of the circuit board, there's a little ring around each leg of the chip location, where you solder the chip. All of these rings are circular except for one, which is square-- that is indeed the corner with the small circle (upper right in first photo). That square pad is pin 1.

Now, pin 20 is the pin at the other corner, which connects to the capacitor-- that pin is connected directly to the capacitor and to the red wire of the battery box.

Your voltage readings here are not self-consistent with one another, nor with your earlier readings. What you're effectively saying is that pin 1 of the chip (which isn't directly connected to the power supply) has a higher voltage (0.97 V) than the power supply (0.47 V), and that the difference between these two points (i.e., 0.97 V - 0.47 V) is 2.4 V.

You may want to try again. Make sure that the battery box is switched on, and start by measuring the voltage across the power supply directly-- the voltage where the two wires are soldered in place. Use the end of the black wire as your ground reference, and measure these voltages again, with respect to that point.


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By: Anonymous: EricS () on Thursday, October 15 2009 @ 10:37 AM PDT  
Anonymous: EricS

Quote by: Windell

I wasn't sure which pin was #1. You said something about a "square pad" but I don't see that unless you were trying to describe the chip itself.

A) I'm assuming it's one of the corners. I noticed that one corner of the chip has a small circle (upper right if the semi-circle edge is pointing right). From this pin to ground I see nearly 1 volt (.97).


My next best guess would be the pin that connect to the capacitor (bottom right if the semi-circle edge is pointing right). Running that to ground reads half a volt, .47.



On the bottom side of the circuit board, there's a little ring around each leg of the chip location, where you solder the chip. All of these rings are circular except for one, which is square-- that is indeed the corner with the small circle (upper right in first photo). That square pad is pin 1.

Now, pin 20 is the pin at the other corner, which connects to the capacitor-- that pin is connected directly to the capacitor and to the red wire of the battery box.

Your voltage readings here are not self-consistent with one another, nor with your earlier readings. What you're effectively saying is that pin 1 of the chip (which isn't directly connected to the power supply) has a higher voltage (0.97 V) than the power supply (0.47 V), and that the difference between these two points (i.e., 0.97 V - 0.47 V) is 2.4 V.

You may want to try again. Make sure that the battery box is switched on, and start by measuring the voltage across the power supply directly-- the voltage where the two wires are soldered in place. Use the end of the black wire as your ground reference, and measure these voltages again, with respect to that point.



Thanks Windell. I honestly appreciate the help.

Indeed I haven't been getting consistent readings from my testing. It seems like I get higher voltage readings from leads on the top side of the board than I do from those on the bottom. Do the various modes offered by the switch account for the variances? Perhaps it's just my technique. One more time...

With the battery box on, the voltage from red wire to black is 3.22 volts.

Across the capacitors leads I also read 3.22 volts.

From PIN #1 (thanks for the clarification on identifying it), to the black ground I am now reading .02 volts. I tested PIN #1 to ground from the top and bottom of the board and got the same reading.

From the capacitor to PIN #20 I'm reading 2.58 volts.

So if I'm seeing voltage of 2.58 volts from the capacitor to PIN #20, but .02 volts from PIN #1 to ground, then is the chip the culprit? Bad chip or bad soldering?





       
   
By: Windell (offline) on Thursday, October 15 2009 @ 11:39 AM PDT  
Windell

It seems like I get higher voltage readings from leads on the top side of the board than I do from those on the bottom. Do the various modes offered by the switch account for the variances? Perhaps it's just my technique.

Yep, just your technique. If you make solid connections, you won't find any voltage difference from the top to the bottom. It's easier to make a solid measurement on the bottom though, so do all your measurements from the bottom side. Stick the probes into the metal firmly to get a good connection.

>With the battery box on, the voltage from red wire to black is 3.22 volts.

Good! Nice fresh batteries still!

>Across the capacitors leads I also read 3.22 volts.

Good! The power from the batteries is getting to the board, and making it at least as far as the capacitor.

>From PIN #1 [...], to the black ground I am now reading .02 volts.

Not good! This is a possible cause (or maybe effect...) of your troubles. But first, there's another mystery to deal with:

>From the capacitor to PIN #20 I'm reading 2.58 volts.

Say what? Pin 20 should connected directly to the power supply, roughly 3.22 V above ground, if that's what the power supply is reading. Since the capacitor has two pins, "From the capacitor to PIN #20" is not really defined. What's the voltage at pin 20 with respect to ground?

(If the chip is not actually getting power-- if pin 20 is not close to 3 V -- then that could be the root cause.)


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By: Anonymous: EricS () on Thursday, October 15 2009 @ 12:18 PM PDT  
Anonymous: EricS

Say what? Pin 20 should connected directly to the power supply, roughly 3.22 V above ground, if that's what the power supply is reading. Since the capacitor has two pins, "From the capacitor to PIN #20" is not really defined. What's the voltage at pin 20 with respect to ground?

(If the chip is not actually getting power-- if pin 20 is not close to 3 V -- then that could be the root cause.)



Strange. I just checked pin 20 to ground. The highest reading I could get was .48 volts (I really jammed the probes in there and made sure not to cross with any other leads). Seems like from what you've explained, that's where the issue is.

When I mentioned "From capacitor to PIN #20" in my earlier post, I was basically trying to test the path on the board that leads from the capacitor to pin 20. My thinking was that if that connection was good, then I should see the same voltage that I saw across the two capacitor leads. Thinking about it now, I suppose it doesn't make sense to test those two points because my tester is essentially bypassing the boards path from the capacitor to pin 20, right?

Do you think I should just unsolder the chip and try again?





       
   
By: Windell (offline) on Thursday, October 15 2009 @ 12:47 PM PDT  
Windell

>Do you think I should just unsolder the chip and try again?

No-- absolutely not. Ripping out parts when you don't know what else to do is the number one way to end up with a dead kit.

> I just checked pin 20 to ground. The highest reading I could get was .48 volts

Yep, that is probably the problem: your chip isn't getting any voltage. There's something screwy between the high-side of the capacitor and pin 20-- it should definitely be the same voltage at each, since they are connected by a wire on the board.

Try resoldering both of those points-- the high side of the cap and pin 20. Add a little fresh solder, and try not to overheat the parts-- keep it to a couple of seconds; make sure that both joints look shiny and wet.

Also, check around for any possible metal debris or accidental connections that could be causing a short circuit.


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By: Anonymous: EricS () on Thursday, October 15 2009 @ 12:53 PM PDT  
Anonymous: EricS

Quote by: Windell

>Do you think I should just unsolder the chip and try again?

No-- absolutely not. Ripping out parts when you don't know what else to do is the number one way to end up with a dead kit.

> I just checked pin 20 to ground. The highest reading I could get was .48 volts

Yep, that is probably the problem: your chip isn't getting any voltage. There's something screwy between the high-side of the capacitor and pin 20-- it should definitely be the same voltage at each, since they are connected by a wire on the board.

Try resoldering both of those points-- the high side of the cap and pin 20. Add a little fresh solder, and try not to overheat the parts-- keep it to a couple of seconds; make sure that both joints look shiny and wet.

Also, check around for any possible metal debris or accidental connections that could be causing a short circuit.



Alright, I'll try it tonight and report back. Thanks!

Speaking of short circuits, PIN #20 does have a bit of a longer lead that is laid flat against the board. It's just long enough to lay over the next wire below it, running perpendicular. Maybe that's where the short is.





       
   
By: Windell (offline) on Thursday, October 15 2009 @ 01:01 PM PDT  
Windell

Speaking of short circuits, PIN #20 does have a bit of a longer lead that is laid flat against the board. It's just long enough to lay over the next wire below it, running perpendicular. Maybe that's where the short is.


Possible; the trace that loops around pin 20 is a ground trace. The lead should not be laid "flat against the board" -- that could cause problems.

However, it's also the case that there must be a *bad* connection, too-- otherwise the capacitor would be at the same voltage as pin 20.


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By: Anonymous: EricS () on Thursday, October 15 2009 @ 05:23 PM PDT  
Anonymous: EricS

Thanks a bunch Windell.

I tried several times to resolder the capacitor and pin 20. Finally, after applying a little pressure to the top side of the capacitor while soldering I got it to light up!!!

Woohoo!





       
   
By: Windell (offline) on Thursday, October 15 2009 @ 05:29 PM PDT  
Windell

Fantastic!

If this sort of problem should recur, and seems to depend on the capacitor position, you might just *remove* the capacitor; the circuit will still work without it.


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By: Anonymous: Michael Pechner () on Thursday, November 19 2009 @ 10:37 AM PST  
Anonymous: Michael Pechner

4.8V from battery box

4.8 across the cap and also to pin 20.

A couple of mV to all the resistors and leds.

I soldered a wire to vcc2. VCC2 to ground 4.8

vcc2 to the CPU side of each resistor, each LED lights. So the LEDS are correctly soldered.

No solder bridges and all the solder joints look good.

What is next?






       
   
By: Windell (offline) on Thursday, November 19 2009 @ 10:46 AM PST  
Windell

It sounds like the program is not running on the chip-- like it's being held in the "reset" state, which can happen if there's an accidental connection between pin 1 and ground. Check the voltage at pin 1 with the power on. Then, turn the power off, wait a moment until Vcc reads zero, and check the resistance from pin 1 to ground.


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