Voice card sound very weak

Hello, I built a ambika a couple of year ago, every thing was fine but a few days ago one voice card (svf) begin to sound much weaker than the others (I had to trace the signal to find that it was actualy sounding) but sometimes the problem occur only after 30 min of playing. I tried to switch all the ICs with another card but it don’t change anything , the only thing i done before was to put some vernish (ok it was stupid and useless).

someone have a idea?

thanks!

There will most likely be a bad joint somewhere. As the unit warms up the connection varies, hence why it happens after a while of use.

Also, check all socketed chips, sometimes a leg can bend under the chip instead of going into the socket. This causes an intermittent connection.