Rubbertoe81
Member
Ok, so I have recently rebuilt my AU-717 based on the brilliant restoration threads by Leestereo and Super Noob.
For reference the amplifier was working ok overall prior to the rebuilt despite many components hanging onto dear life due to being tainted by the corrosive devil glue.
Upon powering it up for the first time after rebuild I believe I saw a small puff of magic smoke appear to come from the tone control board 2720 so I immediately powered it down.
On inspection I quickly discovered that I had accidentally replaced tr12 on the 2720 board with a ksa992 instead of a ksc1845, I rectified this and confirmed that all other transistor subs on this board were correct and installed in the correct orientation.
Upon testing again I have now discovered that I have no audio at all on the right channel on every input. When separating the power and pre amps the right channel does indeed work fine.
All pots and switches etc were cleaned so I’m almost certain they are not an issue here.
I have crudely traced the audio signal using my multimeter and can confirm it enters the 2720 board and is still present at the balance pot but I’m not 100% sure of the path it takes after this, it definitely appears there is no signal coming out of the 2720 board.
Is it possible I have nuked other components downstream or even upstream of tr12 by powering up with a pnp installed in place of a npn transistor?
I have been going over the 2720 board testing most evenly numbered components but cannot seem to find a suspect.
I have since replaced all transistors on the right channel of this board again (with ksc1845 and ksa992) to rule them out and I also even replaced the dual diode (1n4148 pair) once again but still no change.
I checked some of the reference voltages from the schematic and can confirm that I do have the -33v & +33v values on pins 23-26 coming into the board although the voltages found on the smaller transistors seem out of whack. Every junction on tr12 and tr8 was also showing either -33v or +33v.
I am completely stumped as where to look next so any help or suggestions on how to proceed here would be greatly appreciated.
Cheers!
For reference the amplifier was working ok overall prior to the rebuilt despite many components hanging onto dear life due to being tainted by the corrosive devil glue.
Upon powering it up for the first time after rebuild I believe I saw a small puff of magic smoke appear to come from the tone control board 2720 so I immediately powered it down.
On inspection I quickly discovered that I had accidentally replaced tr12 on the 2720 board with a ksa992 instead of a ksc1845, I rectified this and confirmed that all other transistor subs on this board were correct and installed in the correct orientation.
Upon testing again I have now discovered that I have no audio at all on the right channel on every input. When separating the power and pre amps the right channel does indeed work fine.
All pots and switches etc were cleaned so I’m almost certain they are not an issue here.
I have crudely traced the audio signal using my multimeter and can confirm it enters the 2720 board and is still present at the balance pot but I’m not 100% sure of the path it takes after this, it definitely appears there is no signal coming out of the 2720 board.
Is it possible I have nuked other components downstream or even upstream of tr12 by powering up with a pnp installed in place of a npn transistor?
I have been going over the 2720 board testing most evenly numbered components but cannot seem to find a suspect.
I have since replaced all transistors on the right channel of this board again (with ksc1845 and ksa992) to rule them out and I also even replaced the dual diode (1n4148 pair) once again but still no change.
I checked some of the reference voltages from the schematic and can confirm that I do have the -33v & +33v values on pins 23-26 coming into the board although the voltages found on the smaller transistors seem out of whack. Every junction on tr12 and tr8 was also showing either -33v or +33v.
I am completely stumped as where to look next so any help or suggestions on how to proceed here would be greatly appreciated.
Cheers!
