Well it's across the speaker protection relay.
Her'e s the back story. About four years ago, I helped an 87 year old friend organize his garage and he gave a 939 to me for my time. I like any electronic gear and immediately opened it up to check out the insides and clean it. What the hey, I took electronics for a couple of years in Jr. High, and back then I new everything.
The power supply board looked a little toasted around what I'm guessing are the power transistors and heat sink. (D313D and B507D) Some of the resistors don't look as if they were cool dudes either and probably will need to be replaced.
I found the caps next to the transformers were biblical, I mean they were hole-y OK had holes and the magic juice leaked out. Purchased a set of 10,000 uf caps with a higher temperature rating, as that was the only way to hop it up, and installed it -- after -- I took a pictures of the wiring. Memory isn't as good as Jr High.
It worked! And it worked very well powering a set of Acoustat IIs. Then one day an oldies radio station played Peggy Lee singing Fever, and I melted. Never had a stereo I owned have an effect on me. However, it only worked for about three months after that repair. That was over three years ago.
What hadn't been mentioned was that someone had gotten to the machine before me and released some magic smoke, unless Pioneer solders the top half of the fuses to the holders on the power supply board, and some of the wound wiring was soldered to posts, and some solder didn't have the same oxidation as the (I assume) original solder job.
The system's symptoms were popping sound coming from the speakers, loss of a channel, return of the channel, more popping or arcing across the relay (could it be that the relay wanted to be a set of points in an old Chevy?) Then nothing but popping.
So I scanned some of the threads, and found a request for the following information, and have supplied the info below. FWIW, I was using my Jr High RS Micronta VOM and a cheap Harbor Fright digital multi-meter,which can be replaced if the 939 can be user serviced or if someone needs more accurate information.
Here's the info. The 939 stuff is in italics:
<<The protection board is marked " awm-062", and you need to measure the DC voltages on pins :
pin 11, +35v; 33-34.8
pin 2 -13v; -14
pin 1 amplifier output, could be as low as 10 millivolts, or as much as + or - 35v: Varied all over the place when the protection circuit was fired.
pin 3 amplifier output, could be as low as 10 millivolts, or as much as + or - 35v: Also varied all over the place when the protection circuit was fired.
pin 12 is the exception, you need to read the AC voltage here, about 7.5 volts AC. Mine 7.5
ok turn the meter back to DC for the rest of the readings.
ALL readings are taken with the red lead while the black lead of the meter is connected to a metal chassis ground.
The boards are accessed through the bottom of the unit.
Then read the power supply voltages on the power supply board marked: "awr-052" right next to the protection board.
The readings taken by me are listed below in italics.
pin 8 +25v 24.7
pin 6 +47.5v 45
pin 5 +35v 34
pin 11 -25v -25
pin 9 -43v -44
pin 10 -13v -14
pin 4 +13v +13
pin 2 +7.5v +7.95<<
The questions are: can a relative newbie who just built a small JFET pre-amp and enjoys figuring things out, and making things in general, and fixing things, repair this 939 problem?
Am also planning on making a LM3886 stereo from parts and build on it as a hobby through others who've come up with enhancements. I'm not afraid of longer term projects.
If not, any ideas on how much repairs would cost (I'm in the greater L.A. area.
Her'e s the back story. About four years ago, I helped an 87 year old friend organize his garage and he gave a 939 to me for my time. I like any electronic gear and immediately opened it up to check out the insides and clean it. What the hey, I took electronics for a couple of years in Jr. High, and back then I new everything.
The power supply board looked a little toasted around what I'm guessing are the power transistors and heat sink. (D313D and B507D) Some of the resistors don't look as if they were cool dudes either and probably will need to be replaced.
I found the caps next to the transformers were biblical, I mean they were hole-y OK had holes and the magic juice leaked out. Purchased a set of 10,000 uf caps with a higher temperature rating, as that was the only way to hop it up, and installed it -- after -- I took a pictures of the wiring. Memory isn't as good as Jr High.
It worked! And it worked very well powering a set of Acoustat IIs. Then one day an oldies radio station played Peggy Lee singing Fever, and I melted. Never had a stereo I owned have an effect on me. However, it only worked for about three months after that repair. That was over three years ago.
What hadn't been mentioned was that someone had gotten to the machine before me and released some magic smoke, unless Pioneer solders the top half of the fuses to the holders on the power supply board, and some of the wound wiring was soldered to posts, and some solder didn't have the same oxidation as the (I assume) original solder job.
The system's symptoms were popping sound coming from the speakers, loss of a channel, return of the channel, more popping or arcing across the relay (could it be that the relay wanted to be a set of points in an old Chevy?) Then nothing but popping.
So I scanned some of the threads, and found a request for the following information, and have supplied the info below. FWIW, I was using my Jr High RS Micronta VOM and a cheap Harbor Fright digital multi-meter,which can be replaced if the 939 can be user serviced or if someone needs more accurate information.
Here's the info. The 939 stuff is in italics:
<<The protection board is marked " awm-062", and you need to measure the DC voltages on pins :
pin 11, +35v; 33-34.8
pin 2 -13v; -14
pin 1 amplifier output, could be as low as 10 millivolts, or as much as + or - 35v: Varied all over the place when the protection circuit was fired.
pin 3 amplifier output, could be as low as 10 millivolts, or as much as + or - 35v: Also varied all over the place when the protection circuit was fired.
pin 12 is the exception, you need to read the AC voltage here, about 7.5 volts AC. Mine 7.5
ok turn the meter back to DC for the rest of the readings.
ALL readings are taken with the red lead while the black lead of the meter is connected to a metal chassis ground.
The boards are accessed through the bottom of the unit.
Then read the power supply voltages on the power supply board marked: "awr-052" right next to the protection board.
The readings taken by me are listed below in italics.
pin 8 +25v 24.7
pin 6 +47.5v 45
pin 5 +35v 34
pin 11 -25v -25
pin 9 -43v -44
pin 10 -13v -14
pin 4 +13v +13
pin 2 +7.5v +7.95<<
The questions are: can a relative newbie who just built a small JFET pre-amp and enjoys figuring things out, and making things in general, and fixing things, repair this 939 problem?
Am also planning on making a LM3886 stereo from parts and build on it as a hobby through others who've come up with enhancements. I'm not afraid of longer term projects.
If not, any ideas on how much repairs would cost (I'm in the greater L.A. area.