C1 options for AFM strobe board

stangbat

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C1 is bulging on my AFM strobe board. So I'm looking at replacement options and I see that there really isn't a higher voltage bi-polar 100uf cap made that can replace what is on the board. If I'm going to replace the damn thing, my general way of doing things is to fix it right. That means not installing another 100v cap that will also fail.

Has anyone paralleled two 50uf (or 47 uF) 100v caps? It looks like this would be possible because the 50uF caps are smaller in diameter and I think they would fit. Two 47uF caps are even smaller. I've found the following but I imagine someone can find other options.

Parts Express:
50 uf, 100v, 13mm dia x 32mm length

Mouser:
47uf, 100v, 10mm dia x 30mm length

All Electronics:
47 uf 100v is available but no size data is given.

I can't find anything suitable at Digi-Key or Newark. And GPE doesn't have bi-polar caps from what I see.

Any other ideas or suggestions?
 
2x 50uf caps in parallel will give you 100uf. No problem there.

I'm not familiar with that circuit. There must be a reason they're not using a polarized cap?
 
Thanks, Lindsey. If you are curious about the circuit, there is a lot of info here:
http://iobium.com/fixing_the_afm_strobe_board.htm

The referenced documents in the first paragraph have the schematics and some notes on the design.

Thanks for the info! I was actually just looking at the schematic and came back to comment that it's AC and I would probably just double up the bi-polar caps as you've suggested and go for a higher voltage rating.

You can also use caps in series to increase the voltage rating.
 
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Thanks for the info! I was actually just looking at the schematic and came back to comment that it's AC and I would probably just double up the bi-polar caps as you've suggested and go for a higher voltage rating.

You can also use caps in series to increase the voltage rating.

C1 always goes out in this circuit, so it must be stressing it in some way. I think I have room for two 50uF caps so I'll go that route. It costs a couple of dollars more to do it right so I'm going to take that route. Unless someone can point out a 150+v 100uF bi-polar cap. I don't think such a thing exists.

Okay, I take that back. Since I also build speakers, I know that they do exist, but they are extremely large and prohibitively expensive. :D Here's a "cheap" one:
http://www.parts-express.com/pe/pshowdetl.cfm?PartNumber=027-447
 
From what I've read, the consensus seems to be that C1 is over volted. So I guess two 200 uF in series would be the way to go. I don't think that is going to fit.
 
Okay, looking a little closer, I think I can get two 220uF 250v radial caps to fit in series. It would mean drilling a couple holes in the PCB and using one jumper. I have a couple on hand, I may give this a try.
 
From what I've read, the consensus seems to be that C1 is over volted. So I guess two 200 uF in series would be the way to go. I don't think that is going to fit.

That should work fine. Assuming they're 100V caps. There's always a way to make them "fit". Making it pretty could be another story ;)
 
Okay, another question. The 220uF 250v radial caps I have on hand are polarized. From what I'm reading, I can make them non polarized by connecting them in series, positive to positive. If I do this and can make it fit, I'll end up with the equivalent of a 110uF non polarized 250v cap. Does this sound feasible?
 
Okay, another question. The 220uF 250v radial caps I have on hand are polarized. From what I'm reading, I can make them non polarized by connecting them in series, positive to positive. If I do this and can make it fit, I'll end up with the equivalent of a 110uF non polarized 250v cap. Does this sound feasible?

That will work. The only problem will be that the electrolytic caps will have a more variable capacitance and won't necessarily be as close to spec as a non-polarized capacitor but I doubt it will make a lot of difference in that circuit.

I probably wouldn't be putting my eyes inches from the caps when you turn it on for the first time though ;)
 
Here's the repair. I used caps I had on hand that are higher voltage than necessary, but they fit fine and meant I didn't have to buy anything new. My AFM is still apart, the playfield is being restored. Unfortunately it will probably be 4-5 months before it is back together and I can try this out.

C1 measured at 69uF (should be 100uF), so it was obviously on the way out. However, my strobe was working.

Pic showing the culprit. Notice the bulge at the top of C1.

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Two 220uF 200v caps in series to make the equivalent of a non-polar 110 uF 400v cap. They are hot glued together.

dsc6759large.jpg


The final repair. This fits just fine inside the power supply box. Dabs of hot melt glue hold them secure just in case.

dsc6761large.jpg
 
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