My BC2000 take a dump a while back and I just got around to fixing it. The 8 volt regulator circuit in these is a zener holding the base voltage on a small transistor. This arrangement tends to be problematic. As in the transistor tends to die. So here's what I did.
Located Q8, the regulator transistor. It's right next to the crystal on the top board, which makes it pretty easy to find.
Removed R1, a 220 (or 22, hard to tell when it's charred) ohm resistor which connects between the 12 volt feed and the collector of Q8.
Removed R2, a 470 ohm resistor that connects between the 12 volt feed and the base of Q8. At least I think it's R2. It's definitely 470 Ohms.
Removed Z1, the 8 volt zener diode that connects between the base of Q8 and ground.
Removed Q8.
Installed a jumper across where R1 used to be.
Installed a jumper across where Z1 used to be.
Installed a 7808 8 volt regulator where Q8 used to be. Pin 1 goes where the collector of Q8 used to be, pin 2 goes where the base of Q8 used to be, and pin 3 goes where the emitter of Q8 used to be.
I then took a TO-220 sized heatsink I picked up at a Radio Shack clearance sale a few years back and attached that to the 7808. Nice that it had a threaded hole and I happened to have a screw that fit. In retrospect I should have used some wires and mounted the regulator to the center plate like the 12 volt regulator is. I just didn't feel like hauling this thing to the garage to drill a hole in the center plate, then find a nut and screw to secure the regulator with.
I let it run overnight with no covers and it was still working this morning. So I've now put it back in the case and have started a 24 hour burn in to see if it can survive that.
Fairly simple mod using parts I had on hand. Thought it might be handy for someone else if they find their factory setup to be failure prone.
Located Q8, the regulator transistor. It's right next to the crystal on the top board, which makes it pretty easy to find.
Removed R1, a 220 (or 22, hard to tell when it's charred) ohm resistor which connects between the 12 volt feed and the collector of Q8.
Removed R2, a 470 ohm resistor that connects between the 12 volt feed and the base of Q8. At least I think it's R2. It's definitely 470 Ohms.
Removed Z1, the 8 volt zener diode that connects between the base of Q8 and ground.
Removed Q8.
Installed a jumper across where R1 used to be.
Installed a jumper across where Z1 used to be.
Installed a 7808 8 volt regulator where Q8 used to be. Pin 1 goes where the collector of Q8 used to be, pin 2 goes where the base of Q8 used to be, and pin 3 goes where the emitter of Q8 used to be.
I then took a TO-220 sized heatsink I picked up at a Radio Shack clearance sale a few years back and attached that to the 7808. Nice that it had a threaded hole and I happened to have a screw that fit. In retrospect I should have used some wires and mounted the regulator to the center plate like the 12 volt regulator is. I just didn't feel like hauling this thing to the garage to drill a hole in the center plate, then find a nut and screw to secure the regulator with.
I let it run overnight with no covers and it was still working this morning. So I've now put it back in the case and have started a 24 hour burn in to see if it can survive that.
Fairly simple mod using parts I had on hand. Thought it might be handy for someone else if they find their factory setup to be failure prone.
