I have just assembled a MK131 traffic signal kit. While all LEDs do light and oscillate, they do not seem to switch as intended. All solder joints look to be good and there is no bridging (aside from base of T3 to R12 which, judging by the schematics, seems to be correct). I was wondering if this was possibly a problem cause by a bad component, possibly the IC or one of the transistors or diodes? or even possibly a bad trace or pad on the board?
When you say they don’t switch as intended what does that mean?