Tweet
The organ in question has around 70 SAMS (Peterson Powerknobs) dating to 1986. Each unit uses two 1N4003 diodes across the coils for spark suppression. They are actually superfluous since the Syndyne combination action board uses UDN 2981 drivers which have built in diode protection. Nonetheless we left the 1N4003s in place. But a recent failure makes us question that decision.
One of the diodes (partially) short circuited but didn't blow fully meaning it overheated and scorched the PCB to the point where it even lifted the copper traces. At that point the 4 amp fuse on the CA board blew but not before the UDN 2981 was destroyed. Fortunately the SAM could be rewired to bypass the damage and the UDN 2981, which was socketed, was also easily replaced.
Has anyone else had a similar diode fail in this manner even when it wasn't carrying any current but was only being used for spark suppression? I've always though of this series of diodes as being pretty bomb proof and an unlikely source of failure.
One of the diodes (partially) short circuited but didn't blow fully meaning it overheated and scorched the PCB to the point where it even lifted the copper traces. At that point the 4 amp fuse on the CA board blew but not before the UDN 2981 was destroyed. Fortunately the SAM could be rewired to bypass the damage and the UDN 2981, which was socketed, was also easily replaced.
Has anyone else had a similar diode fail in this manner even when it wasn't carrying any current but was only being used for spark suppression? I've always though of this series of diodes as being pretty bomb proof and an unlikely source of failure.
Comment