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jlh3

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Posts: 2
Reply with quote  #1 
Hi, I bought 2 of the assembled CK1614 multimode timers recently. One works as expected, one doesn't. Upon applying power in mode 2, 5 second delay set and with no trigger inputs, the first timer does nothing (as expected), and when trigger+ is pulled up to VCC and trigger- is grounded, the relay operates for 5 seconds and releases (also as expected).

With the second timer, upon applying power in mode 2, 5 second delay set and with no trigger inputs, the relay energizes for 5 seconds then releases (unexpected). When trigger+ is pulled up to VCC and trigger- is grounded, nothing happens (unexpected). When reset is momentarily grounded, the relay operates for 5 seconds and releases. Trigger + and - have no effect.

I examined the board carefully for defects, verified that the 4 transistors, 3 diodes and 2 electrolytic capacitors are functioning normally, checked the IC for bent pins, and swapped the optical isolator with the first board, but can't find an obvious problem.

I called the folks at Carl's Electronics, and they suggested that I post to this forum before asking to have the board replaced.

Any ideas?

jim
Frank

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Posts: 1,890
Reply with quote  #2 
Hi Jim,

I suspect you have a board fault which is causing a permanent trigger input to the MCU. You can verify this by swapping the MCU from the 'good' timer to the faulty timer board. If the fault remains then the fault is on the board.

Do you have a multimeter? If so power up the faulty timer and measure the voltage at pin 6 of the MCU (no trigger input). It should read around 5 volts.

If it reads around 0 volts then you have a board fault. In that case inspect the PCB trace starting at pin 6 to see if you can see a short circuit. The trace should only run between pin 6 of the MCU, one end of resistor R3 and pin 5 of the opto isolator.

Sometimes you can get hairline shorts which are very difficult to see. Use a small screwdriver to scrape any suspicious looking areas, especially where the trace runs close to another component solder pad.

Frank
jlh3

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Posts: 2
Reply with quote  #3 
Frank,

There was, in fact, a tiny bit of solder flashing across pins 5 & 6 of the opto-isolator. Works perfectly now.

Thanks!

jim
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