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- when I removed caps from the boards, I noticed three instances were the glue holding three of the medium sized caps in place had dried up and started to become conductive and generated heat. I did not glue any of the caps in place. What glue or other material would you recommend using to mechanically dampen the vibration in the caps? Note also that I actually was surprised to find this conductive glue in my Oppo DVD player that was starting to create a heat problem between terminals of a power supply cap!
no glue, glue was for large caps in the factory manufacturing environment, otherwise the big caps would fall off/away from the stuffed board before wave soldering, glue is / was purely a factory requirement.
Pioneer's glue has proved to be pretty inert over the years. Heat does make it more brittle, but that was usually an indication of a generally hot environment inside the chassis - poor ventilation by the owner.
Other manufactures used different glues that proved otherwise, usually not as much conductive as corrosive, eating away component leads.
as for polarity, the 1250 has 4 main caps, and I don't have the afternoon required to dig the 1250 out of the place it is in and look at the bottom for the wire colors, so you will need to use the ohmmeter method to determine the polarity of your cap connections. The power output transistors are TO-3 round cased transistors with the case being the collector.
DO NOT ASSUME THAT THE LEFT SIDE CAPACITOR ALIGNMENTS ARE THE SAME AS THE RIGHT SIDE CAPACITOR ALIGNMENTS!!!!!!!!!!!!!!!!!
check to be correct...
The PNP (2saxxx,2sbxxx or MJ21193G with the arrow pointing INTO the base in the symbol!!) power output transistors case is the collector for the NEGATIVE power, thus it is connected to that capacitor's negative lead, and that capacitors positive lead is connected to ground. (in the center of the two caps)
and the NPN (2scxxx,2sdxxx or MJ21194G with the arrow pointing AWAY FROM the base in the symbol!!) power output transistors case is the collector for the POSITIVE power, thus it is connected to that capacitor's positive lead, and that capacitors negative lead is connected to ground. (in the center of the two caps)
SO...
connect one of your ohmmeter's test leads to the unknown polarity wire that is to be connected to the big capacitor's terminals - the wires are short, so they can only go to one place, - then touch the ohmmeter's OTHER lead one at a time to each of the power transistors case's and when you find a continuity, look at the lettering on that transistor.
if the transistor number is a 2saxxx,2sbxxx or MJ21193G it is a PNP and that is a NEGATIVE voltage going to a negative capacitor terminal
if the transistor number is a 2scxxx,2sdxxx or MJ21194G it is a NPN and that is a POSITIVE voltage going to a positive capacitor terminal
