Re: DC503 Not Working


U330B and U330C are the scan clock multivibrator. If these stop or stop intermittantly, the symptoms you describe will appear. U332B is part of the counter which, along with U333 (which you have already changed) controls the display multiplexer. There is a scan clock disable line shown in the block diagram. It may be stuck. Look for bad connections as well as bad ICs associated with these circuits. Try adding an external test point by soldering a 1 foot wire to U330, pin 10 as a start to bring the scan clock signal out so you can see it. Move it around, depending on what you see. I'm looking at the right manual now.

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