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RXRBILL

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Posts: 16
Reply with quote  #1 
I have just assembled the K188 40 second voice recorder from Electronic Kits and it does not work. I have triple checked all component placement and all of my solder points. I am using the suggested power supply from Electronic Kits and have verified the setting of 12VDC and that the Tip is + on the plug. I have also verified that there is 5VDC present on pins 1 & 28 of the IC mounting before plugging it in and re-powering the recorder. The red LED does not light up when the RECORD button is pressed, it does flash twice when the RESET button is pressed, I do hear a click on the speaker when the PLAY button is pressed but no recording, when I press the ERASE button it flashes twice but not 7 times when held down. The IC2 component seems to be very hot to the touch.

I have checked everything I can think of with no success, any help will be appreciated.

Thank you,
Bill Dwyer
av8rdad@aol.com
510-304-5505

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Bill Dwyer
RXRBILL
Frank

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Posts: 1,890
Reply with quote  #2 
IC2 is the 5V regulator that powers the board. If it is getting hot then there is either a short on the board or a component is faulty.

You say you measured that 5V was present on the pins of IC1 before you plugged it in. Maybe you plugged IC1 in the wrong way around. Please check that the 'notch' at one end of the IC is up towards the LED.

Remove IC1 and check is any of its pins are bent up underneath the body of the IC.

With IC1 removed power the board and check if IC2 is still getting hot.
RXRBILL

Registered:
Posts: 16
Reply with quote  #3 
Thanks for the quick reply. I did have the IC1 plugged in correctly. I removed the IC1 again and checked the pins and none were bent.

With the IC1 removed I re-powered the board and verified that the IC2 only over heats when the IC1 is plugged in, it does not over heat if IC1 is removed.

I also re-checked for 5VDC on pins 1 & 28.

I checked all component placement and solder points one more time with a magnifying glass and found no defects.

Nothing happens when the RECORD button is pressed, I also tried using a jumper around the RECORD button with the same results.

Not sure what else I can check, any other ideas?

Bill Dwyer
av8rdad@aol.com
510-304-5505

__________________
Bill Dwyer
RXRBILL
Frank

Moderator
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Posts: 1,890
Reply with quote  #4 
There is a manufacturing defect on the PCB which causes pin 18 to be shorted to ground. I don't think this would cause the regulator to overheat but.....

Look at the top of the PCB. To the right of IC1 you will see resistor R4. The bottom pad of R4 is touching the track that runs next to it. You will need to scrape away part of the pad/track so they don't touch.

Use a sharp knife (box cutter works well) and carefully cut and keep scraping away until the short is gone.

If after all that the regulator still gets hot then I would say that IC1 is faulty. In that case contact the reseller.
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