CV input not responding

(I send this to customer support (case 4035) as well, but do not want to miss the opportunity to ask around)


I just received a second-hand Quad VCA. It seemed to work for a couple of minutes - I had it connected to a Befaco Rampage. It did act a bit strangly, ducking a channel when another’s CV went up, and some bleeding from other CV’s, even with the attenuators down. But I never got the chance to really explore its behaviour because at one point it stopped working: The Befaco Rampage stopped cycling, and the CV inputs stopped responding - only very faintly turning green, and not to any effect. For a couple of more seconds the forth CV still responded when I tried that one out (I had not attached it before), but then also stopped working. My power supply is definitely not a problem, plenty of power left there and no issue with cabling.

At one point I connected it to the busboard with its power on, and it lit the first LED in red (and at a second attempt all four). I had a thought (not sure if this is relevant, or just coincidence) to turn down the attenuators first, and try again, and this time all four turned green. At this point it seemed to respond again. A moment later, when connecting a filter, it showed the same burned-out behaviour again. ‘resetting’ by plugging it in a hot bus did work again, althought the 3rd of the VCAs now still shows the same burned-out behaviour and I cannot really use it like this. The situation now looks as follows. If I connect a CV in channel 1, and turn up the attenuators, only 1,2 and 4 respond. The LED of 3 seems only to very very faintly respond. When plugging CV into 2, 2 and 4 respond. When plugged in to 3, only 4 responds. Also, the very very faint LED response seems to bleed in from 2 as well.

It seemed something is shorting perhaps? It does become a little warm, but I don’t know if that is out of the ordinary.

Some further diagnostic:
When I turn attenuator 1,2 and 4 up, and plug in a CV in nr. 1, I see only 1,2 and 4 respond. Now, if I turn up the attenuator (clockwise) of nr. 3, nothing happens at nr. 3, but all the others stop blinking, i.e. are maxing out. So it seems somehow nr. 3 is perhaps short-circuiting the rest? It does clarify the story :slight_smile: