Hello,
This is my first post.I have combed this site for this problem and I either have a tough one to fix or I missed something so here goes.
I picked this 780 up from a guy for $25 for parts he said he thought it was struck by lightning,so I thought I'd give it a try to fix nothing to loose but time and ordered parts..
1; upon powering it up it clicked immediatly and the right meter went half way up and I noticed a thread of smoke coming from the area of the sips and the nearby resistors.( now I'm going from memory about 20 hours of time,so I may jump from topic)I tested the 2; a979 sips and the 2; c1775 which were bad also sub'd an A844 in place of Q22 a A904 I removed and tested (on a B&K 520B) the 3 regs with the U shaped heat sinks all are good. I replaced PA3004 thats the pioneer ic near the relay and disconnected the 2 0050 ic's the relay problem was cured,it clicked on after a few seconds.I then checked the 4 .22 resistors out of circuit then added the left channel IC and had a click and then sound (yay)then I took the second 0050 installed it and had click and sound (just to be sure the IC's were good)then I resolderd the right IC turned it on and NO CLICK.I re-checked even swap the IC's back and forth L+R to R+L and no go.Even if I try to run the only the right channel and NO chip in the left no click.I took the 3 transistors and 2 sips from the left an put them on the right and still the left channel works no right channel.I have High 34 volt readings on pins 1,2 and 9,10 I don't have that problem on the leftchannel so here I am.The .22's are good and I have checked and replaced some of the over heated but still good resistors that are mounted above the board.I must be missing something or just burned out.
Does anyone have any idea's?
Thank you.
This is my first post.I have combed this site for this problem and I either have a tough one to fix or I missed something so here goes.
I picked this 780 up from a guy for $25 for parts he said he thought it was struck by lightning,so I thought I'd give it a try to fix nothing to loose but time and ordered parts..
1; upon powering it up it clicked immediatly and the right meter went half way up and I noticed a thread of smoke coming from the area of the sips and the nearby resistors.( now I'm going from memory about 20 hours of time,so I may jump from topic)I tested the 2; a979 sips and the 2; c1775 which were bad also sub'd an A844 in place of Q22 a A904 I removed and tested (on a B&K 520B) the 3 regs with the U shaped heat sinks all are good. I replaced PA3004 thats the pioneer ic near the relay and disconnected the 2 0050 ic's the relay problem was cured,it clicked on after a few seconds.I then checked the 4 .22 resistors out of circuit then added the left channel IC and had a click and then sound (yay)then I took the second 0050 installed it and had click and sound (just to be sure the IC's were good)then I resolderd the right IC turned it on and NO CLICK.I re-checked even swap the IC's back and forth L+R to R+L and no go.Even if I try to run the only the right channel and NO chip in the left no click.I took the 3 transistors and 2 sips from the left an put them on the right and still the left channel works no right channel.I have High 34 volt readings on pins 1,2 and 9,10 I don't have that problem on the leftchannel so here I am.The .22's are good and I have checked and replaced some of the over heated but still good resistors that are mounted above the board.I must be missing something or just burned out.
Does anyone have any idea's?
Thank you.
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