I just assembled the TV-B-Gone kit and had a strange problem, when powered on, the green light blinks for over 5 minutes and the IR LEDs just barely turn on. I was testing this using a benchtop power supply rated at 5A and set to 3.7Vdc to simulate a LiPo battery. The current draw according to the benchtop supply was 5mA. Testing the kit with a LiPo battery, two alkaline AA, or two Lithium AA all yielded the same result.
I wasn't sure what the problem was, but I suspected Q5. To cut to the chase, I solved the problem by installing a low ohm resistor (39 ohm is the first one I grabbed) and placing it between the collector of Q5 and the bases of Q1-Q4. This drastically increased the brightness of the IR LEDs, the green light blinks for approximately 55 seconds, and the current draw on the benchtop averages to about 100mA (though it is peaky). Also, I get good indications that it is working on the o-scope.
I suspect that when Q5 turns on, it shorts the power supply, causing a power supply dip and this resets the micro. Thats why the green LED never stops blinking, the micro is constantly restarting. Any other thoughts? I'm really surprised this kit didn't work 'out of the box.' Have others experienced this issue or am I alone in this? I'm posting this in case others experienced this and they can try my solution.
Here is an o-scope shot that indicates the power supply dipout with the original kit.
Strange Problem and Solution
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- uberdude
- Posts: 2
- Joined: Sun Feb 23, 2014 9:04 pm
Re: Strange Problem and Solution
Here is an o-scope shot with the 39 ohm resistor in place between the collector of Q5 and the bases of Q1-4.
Also, since it seems to be the thing to do on this board, here are shots of the front and back, it is very tricky to get a good shot of the back. Q5 was removed for troubleshooting. I realize it looks like the crystal isn't soldered well, but I get a rock solid 8mHz sine wave from it.
Also, since it seems to be the thing to do on this board, here are shots of the front and back, it is very tricky to get a good shot of the back. Q5 was removed for troubleshooting. I realize it looks like the crystal isn't soldered well, but I get a rock solid 8mHz sine wave from it.
Please be positive and constructive with your questions and comments.