Play your file as normal and the signal should appear on the output of IC35 pin#1 - this is fed into a couple of transistors - if either of these fail then the output of IC35 pin#1 will be shorted out.
This signal is passed to the Serial ULA (IC7) pin#12 via a small electrolytic capacitor (C30 10uF) see if there is any signal there. As you have replaced IC35 already, check IC35 pin#1 with an oscilloscope (doesn't need to be anything fancy) and you should see a square wave of the signal (irrespective of the input volume - to an extent)
You can check further back up the chain, pin #2 of IC35 should have a set of square waves on it (pin #3 should be ground) pin #14 of IC35 should have square waves on it and pin #8 of IC35 should have a signal on it too.
If there is no signal on pin #8 of IC35 then suspect the connection between the DIN socket and the board.
BTW:If you haven't got the schematic to the PCB, get it here download/file.php?id=88867
This signal is passed to the Serial ULA (IC7) pin#12 via a small electrolytic capacitor (C30 10uF) see if there is any signal there. As you have replaced IC35 already, check IC35 pin#1 with an oscilloscope (doesn't need to be anything fancy) and you should see a square wave of the signal (irrespective of the input volume - to an extent)
You can check further back up the chain, pin #2 of IC35 should have a set of square waves on it (pin #3 should be ground) pin #14 of IC35 should have square waves on it and pin #8 of IC35 should have a signal on it too.
If there is no signal on pin #8 of IC35 then suspect the connection between the DIN socket and the board.
BTW:If you haven't got the schematic to the PCB, get it here download/file.php?id=88867
Statistics: Posted by maniacminer — Wed Jan 24, 2024 12:41 am