Heindenhain QC300 Doesn´t work fine

Thread Starter


Joined Sep 16, 2023
Good morning team

I have a Heindenhain QC300 device which does not turn on when powered with 120vac. SOMETIMES it turns on when I touch the terminals of the capacitor indicated in the image with the tips of the multimeter or also when I touch the terminals of the oscillation crystal also indicated in the image with the tips of the multimeter.

Tests carried out.

The entire circuit of the source was reviewed, measuring capacitors uf and esr values, diodes and the TOP245, the oscillation frequency of the TOP, 60 KHz, was reviewed.
A 47 uf electrolytic capacitor was replaced.
The 12v, 5v and 17v output sources were checked as well as 3.3v and 2.5v. All the components of the source were re-soldered.
The oscillation crystals of the other ICs work well, tested on an oscilloscope.

The glass that I mentioned above was changed and the IC is a 1670e.

This IC is responsible for starting the LCD and communicating with the external eprom memories. These memories and the IC are backed up with a 3.3 volt battery that is in good condition.

It is important to note that when it is turned on everything works properly but if it is turned off it does not turn on again until some of the two components are touched. and like I said SOMETIMES.

Thanks for the help what any idea may be.



Joined Sep 12, 2023
Test the connections on the PCB, especially around the components you mentioned (capacitor and crystal). Make sure there are no loose wires, solder joints, or connectors. Re-solder any suspicious connections.