K2579 Not stopping

Kits Timers and Clocks
1

When i press ‘start’ the relay closes
when timer runs out, and when ‘stop’ is pressed, relay will not open.

When measured:
when timer started, the voltage on the relay is 12 volts,
when timer stopped, the voltage on the relay is 7 volts and that is probably why the relay will not close.

The problem is that i don’t know why…

I have tripplechecked the position of every element on the circut board.

What could be the problem?

2

Check the transistor. Does the relay turn off when you short the base to ground ?
In that case, replace 555. If not, replace transistor.
Make sure problem is not cause by a soldering error (bridge, short, etc…)

3

Hello

zhanks for the quick response.
It appears that i fried the transistor when i soldered it.

Thanks!