Hi, thanks for looking! The bass player in my band said he had some sort of 'power surge' (ok, he doesn't know what that really means. I think he had opposite polarities on his amp and the PA....touched bass to mic stand, and his amp went poof). I'm trouble shooting it for him. It is an Ampeg B2R, solid state. No power at the preamp yet, so obviously my issues are (at least) in the power supply. Transformer is ok, as is the recto, and filter caps.
I found & replaced a few really toasty power resistors (R67, 68, 69, 70), and the power transistor that switches in his fan (heat sensing circuit, not shown) was LOOSE in the case, so replaced it. I am getting B+ out to the junction of those resistors, and it just dies after them, at the zener diodes (D23 & 24). I pulled the zeners and THEY ARE NOT DEAD, and no shorts to ground or anything. But now I have to order new ones (tragic removal...). The caps after them seem ok, too. So, any ideas why this thing suddenly loses its + and - voltage at that point? The ground is continuous from CT transformer to the case, btw. To the left on this schem is the 3-wire transformer. All seems good w/the bridge recto, all the way up to the beginning of R68 and R70.
Any thoughts?? Thanks!!!
I found & replaced a few really toasty power resistors (R67, 68, 69, 70), and the power transistor that switches in his fan (heat sensing circuit, not shown) was LOOSE in the case, so replaced it. I am getting B+ out to the junction of those resistors, and it just dies after them, at the zener diodes (D23 & 24). I pulled the zeners and THEY ARE NOT DEAD, and no shorts to ground or anything. But now I have to order new ones (tragic removal...). The caps after them seem ok, too. So, any ideas why this thing suddenly loses its + and - voltage at that point? The ground is continuous from CT transformer to the case, btw. To the left on this schem is the 3-wire transformer. All seems good w/the bridge recto, all the way up to the beginning of R68 and R70.
Any thoughts?? Thanks!!!