A few years ago I picked up a Pioneer SA-900’s with the intention of recapping it to mate up with the TX-900. I finally got around to getting this work done last week prior to a little audio gathering by some local enthusiasts… dare I say audiophiles.
Anyway I’ve done this before and generally recapping isn’t all that difficult for the small caps. But I’ll show you how I went about restuffing some of the larger electrolytics.
First off, I confirmed before working on the unit that the Amp did indeed work fine, and in this case it did. By confirming this, if it doesn’t work afterwards, it means I messed up something.
So with the schematic and parts list in hand I ordered up all the caps from Digikey, with some from Mouser left over from a previous project. I tend to pick the caps that in there series or model have the greatest selection to match my needs. I also prefer to use 105C caps vs the lower temperature 85C caps. I know this unit won’t get nearly that hot, but I’ve seen too many 85C caps leak from the servicing of equipment that I’ve worked on over the years.
Replacing the small caps is pretty straight forward. Just use a vacuum desoldering tool and soldering iron to remove the solder from each pad, remove the cap and replace with the new one. Always ensure that the polarity matches when you put the new one in, otherwise electrolytics like to explode. The bigger the cap, the louder the boom. I also don’t replace ceramic caps, or Polystyrene caps. the Polystyrene caps are in clear plastic cases and you can see the silver foil inside them.
For the larger caps mounted on the chassis, there are several ways you can handle these. What makes this challenging is the fact that newer caps are easily half the physical size of 40+ year old devices.
Some options are:
- You can disconnect the existing cap and solder the new one under the chassis, Easy to do, but might not work is space is a problem.
- Try to source a capacitor that fits the diameter of the mounting bracket so you can completely replace the old for the new. You potentially could get a larger value capacitor to fill in the space for the power supply section, but I’m not comfortable changing the value by much more the 50% on a power supply cap. And in the case with a capacitor couple amplifier I really don’t know what would happen if I changed the value at all. So this overall doesn’t work well for me.
- Finally you can restuff the old caps by inserting the cap within metal can of the old one.
I chose to restuff the caps. To do this remove the old cap from the chassis. Remember where the wires go and the polarity of the capacitor.
Next I used a sharp knife to cut the clear plastic shrink wrap near the base and removed it. Reason is that in the next step using some side cutters chews up the plastic cover making a mess of it.
Using some side cutters work under the edge where the aluminum is rolled over peeling it back up.
Work slowly all the way around. Use a pliers to smooth out the edges to make it easy to pull the guts out.
Pulling the guts out sometimes can be really easy. Other times it can get stuck due to the tar like substance that they used to hold the contents in place. If this happens you might have to rock the foil paper from side to side to break it free or warm the cap in warm water to soften the tar.
Next remove the old paper and foil, but save the base. Drill two holes near the leads and are the same distance apart as the new capacitor so you can feed the wires through.
Install the new cap. Make sure the negative matches. Generally a black dot on the old cap leads indicates negative. Wrap the new cap wires around the original base leads and solder.
Reinsert the base back into the original can. Then if you want you can gently roll the corner lip that you opened up back down. You’ll never get it to look like it did, and probably doesn’t need to be in case you ever have to get back in there. I basically held the cap at a 45 degree angle and rolled it against a block of wood to move that lip back about 10 to 15 degrees just to keep the base and can together.
Here are few photos of the power supply cap. The original is a 2200uf cap. I actually used a 3300uf cap and its still considerably smaller then the original. Because of the size of this cap I used a hot glue gun to secure it to the base.