As part of some practical summer holiday work I ordered a K8089 form a supplier in Sweden. The kit was, as all other Velleman kits, well documented and the student built it correctly in a few hours.
We had no 12V AC available to used a laptop DC power supply (18V DC) at the AC input. After the 2 x diode drops, the voltage on the rectifier cap is 15,6V (it would be 16,9V with a 12V AC power supply). We correctly measured the +8V and +5V at the various IC’s before installing the silicon. All works fine, but after 4hrs we noticed a 4 minute drift (K8089) runs behind. After 24 hrs the K8089 was approx 28 minutes behind…! The PIC must be using its internal RC oscillator as there is no Xtal on the board. How can we correct/calibrate the time keeping ?
No temp sensor is fitted.
Regards SA6BUQ.