My Taxi is having problems booting. And by "problems" I mean "won't boot at all".

When I power it on, the GI comes on, and the kickers fire once after a really short delay. Nothing comes up on the display. The speakers have a really loud buzzing. One of the three LED lights flickers briefly (never the same one consistently) once or twice, but none of them ever really act as they should. Neither of the buttons on the MPU board work. This thing is dead. Dead, dead, deadski.

So, I figured I'd post the symptoms before I start really digging into it. The first thing I'm going to figure out is why the blanking signal isn't working. Does that seem like a good starting point?

Negative.

I'm pretty sure this board doesn't have any alkaline damage. There weren't any batteries in it when I bought it, and I don't see even a trace of battery junk anywhere on the board. Not even in the battery holder.

I really, really don't think it's alkaline-related.

OK! We've had a development.

I turned the power on, clipped the black lead to the ground braid, and took measurements on the three test points on the power supply, with nothing plugged into it. The +12V test point was fine at around 13 volts. The -12 was reading zero. Maybe that's OK, since the -12 required power to be coming back in from somewhere, right? And the 5V test point starts at 1.5 volts and climbs steadily up to about 2. That certainly doesn't seem right.

It's real quiet in the house today, so while I was measuring voltage, I was hearing a strange noise. I can't really describe it other than it sounded like something expanding. I thought it was possibly the giant heat sink on the power supply. The thing is, it was stopping immediately when turning the power off. That's odd. Then, as I was trying to set up a lamp and my phone to record the noise, the radial capacitor at C9 popped. It was... loud. It also smells like ass.

So, there's a problem. Something caused the C9 capacitor on my power supply to pop. Now I need to look up what runs through that capacitor and find out what caused it to pop.

I don't think so. I replaced all the caps in the power supply last year. Something else might be going on that caused it to blow.

I just pulled the capacitor out, and there's no leakage at all. The top is popped open a bit, but there's nothing coming out of the base.

How should I go about testing this? I can go t another capacitor. Should I figure out a way to use alligator clips so I don't have to re-solder it in? Or is that too much hassle?

I was also thinking that it's a bad bridge rectifier.

Here's the power Supply diagram.

PowerSupply (resized).jpg

C9 is right by TP2 in the lower left. I'm having a bit of trouble reading the diagram as far as the bridge rectifier is concerned.

It looks like the -12v comes from 3J1-14 and 15, and comes into the negative side of C9. This lines up with one of the points on the bridge rectifier. The bridge rectifier looks to take its AC from the top and bottom. Does that mean the right and left are the positive and negative of the resultant rectified current? If so, then that lines up with the negative of the 12v as they both go into the negative side of the capacitor.

With all the stuff that uses the +12v unplugged, that means there's no -12v current coming in, right? If so, then the only current coming into the capacitor was from the bridge rectifier. This means I probably have a bad rectifier. I'll look into how to properly test them. Do these go bad often?

OK, I've tested the bridge rectifier in the board with nothing plugged into it. I'm calling the AC points AC1 and AC2.

DMM red to bridge '-'
.5v to AC1, 0.0000v to AC2

DMM black to bridge '+'
.5v to AC1 and AC2

DMM black to bridge '-'
0L to AC1, 0.0000v to AC2

DMM red to bridge '+'
0L to AC 1 and AC2

I'm pretty sure that 0L on my meter means completely open, whereas 0.0000 means a really small amount of current is making it through. If that's the case, then I think this is a leaking rectifier, and it needs replacement. Do you guys concur?

The problem rectifier has been replaced, along with the two on the auxiliary board. Now, it seems the machine is only giving me half of the channels when it plays sound. No drums on any of the music tracks during the test, and no warning buzz when I turn the machine on without batteries.

I'll start a new thread for it.