SOLVED: Sad Clown! Exidy Circus is misbehaving. Help finding a bridge rectifier replacement?

jimbodeanny

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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?


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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?
 
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I also wonder if I could use a switching power supply just for the 5V to test the PCB?

Yes, this first before you touch the PCB.

Sounds like you've done a lot of work already, The rectifier looks to be a 50 VDC 6 Amp single phase rectifier. Not sure what the package is called, should be easy to find on Mouser.

Or, https://www.ebay.com/itm/224407217396 Or someone here might have one?
 
Yes, this first before you touch the PCB.

Sounds like you've done a lot of work already, The rectifier looks to be a 50 VDC 6 Amp single phase rectifier. Not sure what the package is called, should be easy to find on Mouser.

Or, https://www.ebay.com/itm/224407217396 Or someone here might have one?

Cool. Yeah that's what I was thinking. Definitely going to try that when I have time. I'm just digging through the game & monitor manuals, trying to figure out if I still even need to have that little board/PSU installed at all. There doesn't appear to be a schematic for it that I can find anywhere.

There are four terminals to the right of the fuse holder. The first two are labeled "AC" and seem to go to the giant transformer. The other two terminals, "red" and "blk" are the 5V. If I'm understanding this correctly, the board seems to pull power from the +73v on the monitor chassis. But I can't seem to find what those two AC terminals that connect to the transformer are for and if it's crucial that I have them connected to this board. The same transformer has a two-pin connector that runs into the chassis that I would guess is what powers it.

Anyhow, I'll keep digging and hopefully find an answer.

Thanks
 
Well, I took a closer look at the M5000 manual and it appears that the T3 transformer supplies power to the monitor via the P3 connector as I suspected. I double checked the wiring to the transformer and it seems to confirm this and so I'm not really sure what those AC terminals on the 5V supply board are for, but it doesn't seem crucial to powering the monitor or PCB. So, I think it's safe to test everything without that little board attached. I'll post after I have some time to test it.

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You could go to an 8 amp or 10 amp rectifier. It will run cooler generally.
 
Google says VHO48 is a 6 amp rectifier. Anything that much or bigger will work.


The only detail is finding one that matches the pin spacing, though that's not super critical, as you can just bend the pins slightly if needed. This one should work. The spacing is a hair bigger than the VHO datasheet (12mm vs 10mm), but it should still fit:

 
UPDATE:

Used a switcher for the 5V to test everything, and low & behold everything fired right up and worked 100%. Thankfully, it was just the 5V power as I [mostly] suspected and the PCB is just fine. *Sigh of relief*

All that's left is getting a replacement rectifier and rebuilding that little 5V supply. For now, the switcher will suffice.


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