Hello all,
I need some advice on a situation I've gotten myself into. I restored an A-1020 that I found online (blown outputs and resistors) as well as completed a full recap. Everything was all and good for about two months until I pushed the class A button. Fuse blew and protection was activated. With the little "driver boards" out, I can prevent the fuse from blowing, but I still have -5vdc and -15vdc across the outputs which is keeping it locked in protection. I've been digging for the source of this dc in the signal path and I'm coming up empty handed and confused. I'll note some of the places I've found the voltage and been stumped.
Between C208 and C210 I measure 4.25vdc, which seems to be the beginning of where I find it, but it can only come from the node right of R212 which is connected to so many other things I'm not even sure where to start looking next.
In addition, D214 is supposed to have -60vdc on the anode and 1.7 on the cathode (which connects to points e, b, and c to control the transistors on the now disconnected driver board)...yet I get postitive 62vdc on the cathode...which is nearly full rail voltage. No idea where it's coming from since the only other point connecting to that diode is C230, which has 0V on the leg connected to the ground bus and the same +62vdc on the leg connected to D214s anode. The dc seems to appear put of nowhere.
I'm at a bit of a loss here hoping one of you kind folks can point me in the right direction.
I need some advice on a situation I've gotten myself into. I restored an A-1020 that I found online (blown outputs and resistors) as well as completed a full recap. Everything was all and good for about two months until I pushed the class A button. Fuse blew and protection was activated. With the little "driver boards" out, I can prevent the fuse from blowing, but I still have -5vdc and -15vdc across the outputs which is keeping it locked in protection. I've been digging for the source of this dc in the signal path and I'm coming up empty handed and confused. I'll note some of the places I've found the voltage and been stumped.
Between C208 and C210 I measure 4.25vdc, which seems to be the beginning of where I find it, but it can only come from the node right of R212 which is connected to so many other things I'm not even sure where to start looking next.
In addition, D214 is supposed to have -60vdc on the anode and 1.7 on the cathode (which connects to points e, b, and c to control the transistors on the now disconnected driver board)...yet I get postitive 62vdc on the cathode...which is nearly full rail voltage. No idea where it's coming from since the only other point connecting to that diode is C230, which has 0V on the leg connected to the ground bus and the same +62vdc on the leg connected to D214s anode. The dc seems to appear put of nowhere.
I'm at a bit of a loss here hoping one of you kind folks can point me in the right direction.