Yorkville-AP-Series-Quick-Repair-Guide

The Yorkville In-House Method for Repairing AP Series AmpsAt Yorkville,we have developed a method of rebuilding AP seriespower boards in the shortest possible time.This method is valid forrepairing about 95%of all AP amp failures and is essentially the sameprocess for each of the different models in the AP line.This process was not designed to correct problems other than blownoutputs and collateral losses.We still see an occasional failure in otherareas,but about 95%of all amps that you receive in PROTECT mode,will benefit directly from this method.This uniformity of approach is possible because all AP series ampsshare the same basic circuit topography and protection circuits.Therail voltages and the number of output devices may change,but overallthey remain more alike than they are different.Only the AP800AP1020 have enough differences to warrant a comment or two.The entire program rests on the ex perience we gained while rebuildingthese boards.What became apparent was the fact that we needed tofocus on rebuilding the board and not trying to ANALYZE theproblem.As you can imagine,this practice goes against just abouteverything we have practiced as repair technicians.But,by using thismethod,we were able to reduce turn-around time and expense by morethan 50%.In fact,with practice,an average technician can do a fullmeltdown rebuild in about 90 minutes.The exception to this rule wouldbe the AP 6040,which runs about 3 hours for an average rebuild.The root of this system is the practice of NEVER measuring TO-92 styletransistors.They are always replaced because it takes about 5 minutesto replace them and they cost next to nothing compared to the cost ofanalysis and the risk of a failed rebuild.I instituted this policy afterdiscovering that these little transistors have a really nasty habit of "half-failing".By this I mean that we were testing these things in the normalfashion and they were showing "good",but when powered up tooperating voltage,they would do all kinds of inexplicable things.Assoon as I mandated the practice of always replacing these littletransistors,these strange post-rebuild malfunctions disappeared anddepartmental efficiency went way up.