Mackie_SWA_Diode_Swap_Service_Note

LOUD Technologies Inc.Date:6/04/2008Subject:SWA 1501 Amplifier Service BulletinAuthor:John HolmeRevision History:6/04/2008Initial DraftFirst RevisionSecond Revision12/10/2008Third Revision,Scott PatersonAffected ProductsSWA 1501 [All serial numbers]Failure DescriptionSWA 1501 amplifier section,failing multiple times in short timeframes.Units fail to pass signal and sometimesactually emit smoke.CauseThe misprinting of reference designators D19(zener diode P/N:82131050)and D20(BAV21 diode P/N:82112002)on the printed circuit board causes the problem,as the two locations numbers are swapped on thesilkscreen.The correct components are being oriented correctly,but end up being in the wrong place.Thepicture below is an example of the INCORRECT silk screen.The CORRECT silkscreen sequence will be:R27,R28,R29,D19,D20,R30,D21etc.ActionWhen an SWA 1501 is being repaired for any reason,please look at the amplifier assembly and specifically atlocations D19 and D20.If the locations are reversed from the schematics,install zener diode P/N:82131050 inD20 and install BAV21 diode P/N:82112002 in D19.SimplificationThe location next to R29 should have the Zener diode P/N:82131050 installed.The location next to R30 should have the BAV21 diode P/N:82112002 installed.Orientations are indicated by the silk screen,as this is correct.1of2