Polaroid SX-70 - End of the tunnel

[bwesso]

Hi all - I am at the finish line of a months long refurb of my Polaroid SX-70 and am hung up on one last weird issue.

I had to replace the large body ribbon cable at one point and fear I may have slightly damaged a connection in some way during other tweaks. In its current state, the camera only works if there is a wire soldered between the highlighted contact and the S7 negative contact (see the yellow on my sad diagram). The weird consequence of this is that if you insert a film pack it will trip S7 immediately before even closing the front roller door and eject the dark slide. This is very easy to work around - the camera works totally normally otherwise, but I am concerned about potential battery drain and would rather the damn thing just work right.

I can see through this diagram that the S7 contact goes to ground on the main PCB, do you all think this is some issue with S8 not being grounded? Circuitry escapes me. Curious if anyone has any theories

 

[koraks]

As shown in your diagram, the yellow wire will result in +6V being shorted to GND with the switch (the one in the lower right corner) in the marked position. If that's actual battery +6V and battery minus, this means it effectively shorts the battery. I'd expect the camera not to power on and the battery to run hot. Given that the camera does turn on, I take it that there's an error in your diagram somewhere.

 

[bwesso]

@koraks Sure enough, I mislabeled it. The wire I jumped is actually connected between two S7 lines which is more confusing to me. The same behavior occurred when I soldered one to the ground pad instead of that upper left location

 

[koraks]

The modification you did is the same as permanently keeping switch (?) S7 pressed.
How the behavior you're seeing can be explained, I wouldn't know. I assume the connections Sx-etc. go into a microcontroller and that's a black box.

 

[bwesso]

Solved: just needed to resolder that connection on the S7 switch was not fully making contact to the ribbon cable

 

[koraks]

Glad to hear it was a simple fix!