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Crb3693

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Posts: 6
Reply with quote  #1 
I think the PIC Flasher k169 kit I have has faulty components in it. I had the test setup with 8 LEDs running/blinking fine and then there was a crackle sound on the board and now it doesn't work anymore. The k169 chip was extremely hot but all of the other components looked fine/no bubbling or blackened parts. I had 9 volt battery running the board and 12v 2.5 amp power supply running the 8 LEDs. I just bought this in the beginning of May, can you replace it or send me replacement parts? I've attached a picture of the kit working fine (before the crackling) if that helps...

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Frank

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Reply with quote  #2 
If the LEDs were running/blinking at all indicates to me that the board was fine.

Crackling sounds with electronic equipment usually means a high current pulse through the board, usually as a result of a short circuit somewhere. That usually leads to PCB traces being blown off the board and/or components being charred.

Remove the ICs and check them closely. Also check the PCB for signs of missing traces.

Looking at the photo you may have accidently shorted a couple of the LED leads together which may have caused the problem. There could also be a solder short on the board, especially around the 12V LED supply connection.

You need to do some testing first to try and find the fault.

Connect the 9V battery but not the 12V supply. Check that the 5V regulator is working. You should measure 5V across pins 5 and 14 of the PIC micro.

You can test the 2803 LED driver by removing the PIC and connecting the 9V battery and the 12V supply to power the LEDs. Using a piece of wire connect each input pin of the 2803 (pins 1-8) in turn to +5V (pin 14 of PIC) - the corresponding LEDs should light.

If the 5V supply is fine and the LEDs are working manually then problem is most likely a damaged PIC micro.

The board was working to begin with so don't see why DIY is responsible for any damage caused after that.
Crb3693

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Posts: 6
Reply with quote  #3 
I get 5 v across pins 5 and 14 of PIC micro. None of the LEDs are working manuallyby connecting 1-8 on 2803 to PIC +5V. Not sure i have the pin layout correct though. I believe you should be liable for faulty parts because the circuit worked fine just sitting there while i took the picture and then it just crackled and stopped blinking lights. There is no short in the led wires, the picture is misleading, one wire is above the other. I am thinking one or both caps under the PIC are bad but i see no charring on them or on any of the resistors. What next?

Chris Brown Jr.
Frank

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Reply with quote  #4 
What makes you think some parts were faulty?

The major reason for kits not working are incorrect parts placement and/or poor soldering. Faulty parts are extremely rare. Not saying it is impossible but HIGHLY unlikely

It seems like you are unsure about the pin layout of the 2803 when testing the LEDs. You really need to make sure that you are doing it right so we can determine if the 2803 chip is damaged or not.

As it stands at present we have no idea just which parts are faulty. Basically it would mean replacing the complete kit, which I think is unreasonable.

I am happy to repair the kit for free if you are willing to send it to me. All I ask is that you pay for return postage. However I am in Australia so the postage costs and time delays need to be taken into account.
Crb3693

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Posts: 6
Reply with quote  #5 
I've already ordered 2 more of these kits. They should be arriving today or tomorrow. I'd rather you give me tips on how to troubleshoot this board to find the issue. I'm certain its a bad component. I can replace the resistors or the caps from my own inventory but if its either the 2803 chip or the PIC chip, then i don't know where to get a new one that is dependable so I was hoping to get them from you. Do you have a pin layout of the 2803?
Frank

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Reply with quote  #6 
Datasheet for 2803 here - http://www.ozitronics.com/data/uln2803.pdf
Crb3693

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Posts: 6
Reply with quote  #7 
I had the pin layout right after all. No lights when i connect PIC 5v to each pin 1-8 on the 2803. What can I check next?
Frank

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Reply with quote  #8 
I assume you tested under the following conditions:
1. PIC removed from socket
2. 9V battery connected. This provides the 5V supply to test with - keep checking the 5V supply as the battery will get flat.
3. 12V supply connected to power the LEDs. You need both + and - of this supply connected to the board.

If all the above is correct then seems like the 2803 is damaged.

You can verify that the 12V supply and LEDs are OK by removing the 2803 (power down first) and then connecting a wire between ground and each of the 2803 outputs in turn. They should light. This will also verify that the PCB traces are OK between the 2803 outputs and the LED connections.

You can test the PIC by directly connecting the LEDs to the PIC outputs. This is easy to do - simply remove the 2803 and jumper each input and output together (the pins are directly across from each other). You will also need to only use one LED per output and turned around so the anode is connected to the PIC output. Also the other end of the LED (cathode) connects to ground (not +12V). This is because the PIC output will be high when turning on the LED. The battery may not last that long as it is now powering the LEDs so have a new battery on hand as a backup. Alternatively you could power the kit from the 12V supply you were using for the LEDs.

If the PIC is working then each LED should light as per the DIP switch settings.
Crb3693

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Posts: 6
Reply with quote  #9 
I figured it out. I jumpered all the outputs together and verified the PIC works. I ran the other tests you suggested and concluded that I have a bad 2803 chip. I happened to receive my other 2 kits today so I tried the 2803 from one of those and it worked. How can I go about getting the bad one I have replaced?
Frank

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Reply with quote  #10 
I will send you a replacement 2803 chip.

I have emailed you direct and included my email address. Please reply with your address details.
Crb3693

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Posts: 6
Reply with quote  #11 
Done. Thank you!
Frank

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Reply with quote  #12 
Airmail posted yesterday.
johngreiner

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Posts: 1
Reply with quote  #13 
I have a working K169 PIC flasher board.
I see a reference to using 2 power supplies, 1 for the board (9-12) volts and a separate
supply for the LED's.  The kit instructions do not show how to do this.  Apparently as
you add LED's to strings, the voltage for them has to be increased by 1.8 volt per Led.
How is this done. I am trying drive 30 to 80 leds in my R2D2 dome using 12 volts to the
board.
Frank

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Reply with quote  #14 
You need to arrange your LEDs in groups of 8 or less. Best to keep the number of LEDs per group equal, even if you have to add extra LEDs to do so.

The LEDs in each group are wired in series, with the cathode (K) of one LED wired to the anode (A) of the next LED, etc, as follows (please excuse crude diagram):

A --|>|---|>|-- ~~~~~~~ --|>|-- K

When done you should have 8 "strings" of LEDs with equal numbers in each string.

Connect the anode (A) end of each string together and wire to the COM pin on the PCB.

The cathode (K) end of each string connects to one of the 8 outputs on the PCB.

The positive lead of the LED supply connects to the screw terminal block labelled "9-45V", with the negative lead connected to the "GND" screw terminal block (together with the negative lead of the board supply).

The required LED supply voltage depends on the number of LEDs per string. You need to allow 1.8V per each LED in the string.

You also need to allow some voltage for the current limiting resistors. How much depends on the value of the resistors used and the operating current of the LEDs.

For example:
Let's assume 10 LEDs per string.

The kit is supplied with 470 ohm current limiting resistors. If the LED operating current is 10mA then the voltage drop across the resistors is 4.7V (470 x 10mA). The LED string needs 18V (10 x 1.8V). Therefore the LED supply needs to be 22.7V (4.7 + 18).

Don't worry if the supply you have is a higher voltage. The operating current range of LEDs is quite large (consult LED datasheet) so the supplied 470 ohm current limiting resistors may be enough to keep the LED current within that range. If not then simply increase the resistor value.

For example:
If your LED supply voltage is 30 volts then the resistor drop 12V across it (30 - 18). With 470 ohm resistors the LED current will be 25.5mA (12/470). If this is too much for the LEDs then increase the resistor values accordingly to get the current back in range.


JohnG

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Posts: 193
Reply with quote  #15 
@John Grenier... see the attached circuit diagram (presented for inspiration).   Frank gave you a technique for wiring for "high" voltage.  Mine is for "low" voltage.

I wanted to use a 12V supply with lots of LEDs, so wired the LEDs in series-parallel.  I had an old clock case, and cut a new plastic face panel for it, for the LEDs.  The display was quite spectacular.  

The LEDs draw minimal current, so you should be able to add a couple more sets in parallel easily.  If you run the LEDs at 10ma, then each parallel set should draw 80ma (8 legs x 10ma).  So, 4 x 80 = 320ma.  This is well within the 2803A rating (500ma per leg).  Just make sure your power supply can handle the load.  


hth,
John

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