Our Exidy Circus decided that today was the day for it to give us hell.
I had the game on for a bit and suddenly the image went bonkers, and the audio went into a massive feedback/hum/squelch. I shut the game off, unplugged the edge connector and started inspecting. I suspected it was something with the 5V power supply, but I verified that the monitor was fine and had the 73V - which it did. I also tested the fuse on the power supply and it tested fine. Next, I tested the 5V at the edge connector and then at chips on the PCB. Long story short, the 5V adjustment seemed odd. Although, I could adjust it, as soon as I'd approach 5V on the PCB, the game would get even more wonky with garbage and an unstable image.
Here's a video of the power cranked to 5V on the PCB.
And then a little lower...somewhere in the 4.6v range I think.
The weird thing is that as soon as lower the voltage way down to like 4.2V, the image calms down and I get a more stable image with something resembling Circus a bit more, albeit there's lots of garbage still and the game eventually freezes. Once I start bumping it back up, things go wonky again.
Here's a video at lower voltages. NOTE: I have the speaker unplugged due to the annoying feedback.
At this point, I'm testing the other voltages and whatnot. I'm now wondering if I have a board issue, as I discover that although there's 5.15v at the edge connector, when I test a chip, all I get is like 4v. It's then that I discover the fuse has now blown on the little power supply board. I try another and it also blows immediately so I pulled the monitor out and the power board to inspect. Since there's not much on this little board, I test just about everything, including the bottle cap transistor.
Everything seems okay, except for this bridge rectifier, which has a short. However, I'm having a hard time figuring out what kind of replacement will work?
At this point, I'm not sure if it's just a power supply issue or a PCB issue or both. *SIGH* I'll probably test some components on the PCB (resistors, diodes, etc) but board repair is a little out of my wheelhouse. I sure wish we had a second working PCB for situations like this. Anyone have one for sale?
I also wonder if I could use a switching power supply just for the 5V to test the PCB?