TPD gone bad

[duncandisorderly]

garbage in the matrix & the numeric displays, & the LEDs on the seq itself are flickering, buttons non-functional. sequencer happily playing though.

 

when I unplug the TPD, the sequencer is back to normal. sometimes when I plug in the TPD, there's nothing at all, other times the displays will light up but not moving or with anything useful in them.

 

I'm guessing one of the 595s has gone bad, but it's going to be tricky to isolate the culprit as they are connected in parallel & some of them are hiding. :-/

 

I *think* the problem is with one of the 74HC595s that I can actually get at.... I've carefully cut the track where it goes up from the socket to U2 & this has stopped the TPD from interfering with the sequencer's control panel, suggesting that one of the clock signals is being shunted or held high by either U1 or U2.

 

anyone else had a problem like this?