As you know, I have recently started using the old Polaroid SX-70. The camera is a marvelous instrument, though discontinuation of the film made it necessary for various hacks to be applied for continued usage. The one I will talk about here is the capacitor change. The photos here are from a document I found online, prepared by Joshua Ray Caldwell. I would take my own pictures, but I just put the whole thing back together so am not keen to take it apart. You might also want to check out basic desoldering skills here.
Opening Camera and Identifying Capacitor
The camera opens up after you unscrew the four Torx T4/T5 screws at the back. Some cameras apparently have square-sockets so check before using. The pictures below are, again, from Caldwell’s document.
The front of the camera (with lens) should fall forward, with a solenoid on the right side (note: all lateral, top/bottom, and fromt/back notation is from the perspective of someone standing behind the camera). I think there may be wires running through this solenoid, so don’t let it dangle.
Next, there are some flash contacts to unsolder. These are located on the top of the camera PCB.
What nobody tells you is that when desoldering, there will be some residual solder left on the PCB pad and the pins, so in order to bend the pins upwards (to facilitate lifting PCB off the front assembly), you have to apply heat while simultaneously prying the pins up using a blade. This is pretty easy to do, but took me a while to figure out.
Next, you can locate the capacitor at the bottom left. It will, typically, lowest pair of soldered pads:
You can only remove this much solder, so what I did was to flex the PCB ever so slightly, simultaneously applying the soldering iron on the leg of the capacitor, while applying downward pressure using the iron on the capacitor packaging (this should pretty much destroy the capacitor). Repeat for other capacitor leg, and you should get a pretty burnt capacitor. With any luck, you would have avoided touching the front/back of the capacitor. There you will read the capacitor rating. Mine read “681, 200V”, which means that it is a 680 pF capacitor, rated for 200V (e.g. 681 = 68 x 10 = 680 pF; 104 = 10 x 10000 = 100,000 pF). The conventional wisdom is to use a capacitor with a higher voltage rating (so that it can store as much charge as the original capacitor), but I tried a 50V capacitor and it worked fine (this means that the 200V capacitor is probably over-spec’ed, or that I may be getting inconsistent exposure but not appreciably so). So I used a 151, 50V capacitor (680/4 = 170 ~ 150 pF; a 180 pF will work as well, methinks).
Resoldering New Capacitor
If your soldering skills are better than mine (it probably is) you can probably see the through-hole right about now. You can then trim your capacitor legs to the requisite length and thread them through the hole (hence through-hole technology) and solder from the back side of the board (i.e. the side you have access to). If you cannot see the holes, and cannot remove enough solder to, and have already damaged the PCB board substantially, you will want to try the following. Using a small ceramic capacitor, I cut the legs and bent them such that the whole capacitor lies almost completely flat along the back of the PCB (opposite side from the original capacitor) and soldered it on straight. This works because i.) capacitors are not directional, and ii) the electricity will conduct through the solder on either side of the PCB. This also makes it easier to swap out capacitors in case the 150 pF capacitor does not work. Obviously, the capacitor must be very small, otherwise the camera front assembly will not screw on correctly and your focus will be way-off!
So how well does it work? Why don’t you take a look at my flickr photostream? The shots were taken without any ND gels, and mostly shot with neutral exposure (no under/overexposure on the adjustment wheel). I think this works pretty well!