Looking for a SP7T Rotary Switch - Page 1
Forum section: electronics / beginners

author: LoveLaika
author_rank: Frequent Contributor
timestamp: March 24, 2022, 08:28:19 pm
content: I'm trying to repair a DC power module. The actuator for one of its switches broke off, so I'm looking for a new one. I've attached images of the broken rotary switch and the footprint that it was soldered to. Can anyone help me find an identical one?From what I gather, I'm sure that this is a switch, not an encoder. It appears to be a single-pole 7-throw (SP7T) switch based on comparison with a functional supply. In the footprint photo, I've marked it up showing the pole (as 1) and the seven positions marked by a red dot. The ones marked M appear to just be mounting holes. Despite the nature of the switch, the footprint has five unpopulated holes making me think that one could swap this out for a 12-pole variety. On a functional board, the five lower holes on the footprint were not soldered, so this still remains an SP7T switch. This isn't something expensive, but I can't find something like this on Digikey, especially with the inner holes the way they are. There are no discernable markings that would show who the manufacturer is.With regards to the footprint dimensions, the hole-to-hole diameter is ~12.78 mm for the outer holes across from each other. The inner three holes are separated by a distance of ~7.74 mm from each other. The component itself has a diameter of 18.5 mm, and you can see a little nib showing the location of position 1. The actuator is normally covered with a separate knob.

author: madires
author_rank: Super Contributor
timestamp: March 24, 2022, 08:42:17 pm
content: Looks like a standard rotary switch with one pole and 12 positions. The footprint would also support a three pole with four positions. Those rotary switches have a special washer with a pin to limit the number of positions. For seven positions you would get the one pole 12 positions type and limit to seven. AFAIK, the switch types avaiable are 1/12, 2/6, 3/4 and 4/3. And they come in two variants, with pins for PCB mounting and eyes for soldering wires.

author: LoveLaika
author_rank: Frequent Contributor
timestamp: March 24, 2022, 09:51:33 pm
content: Quote from: madires on March 24, 2022, 08:42:17 pmThanks for your reply. I've attached a picture of the switch's internal workings. It doesn't look like a washer per se, but you can see how there are 7 populated contacts. That little nib in the center, I think it goes within the spring inside the knob, though I can't say for sure. Plus, I'm not sure what its function is. I don't know what stops the switch from turning more than 7 positions.Actually, upon closer inspection, the center pins are connected together. I've attached a picture of the underside of the internals. Apologies for the poor view, but the center contact (the single-pole) has six contacts in the center, all connected. I think three were cut off leaving only three remaining in the actual device.EDIT: Okay,I was wrong. The little nib goes on top of the spring, acting as an internal bridge of sorts between the inner and outer contacts. I found this out while looking at another switch from another module. I plan to take the working switch and transfer it over to the other, but I wanted to know what kind of switch this is in case I need to buy it in the future (and most likely, I will have to).

author: LoveLaika
author_rank: Frequent Contributor
timestamp: March 25, 2022, 01:51:44 pm
content: I see what you mean by this being a standard switch now, though I don't think using the alternatives that you suggested would work. The inside of the part is a single pole, though when you look at the underside, there are six contact points (inner circle) for that pole (with three being cut off in my case). Regardless, the three holes for the single pole on my footprint are not connected on the board. They would have to be connected internally of the switch, so using anything other than a single-pole wouldn't work.Plus, there's the issue with the footprints. The distance between the pole contact(s) and the throw points don't seem to follow any standard pattern. They seem to be closer to one another than on other similar components.Actually, based on a closer inspection of the inside, I'm looking for an SP12T switch where the center pole has six contacts. From there, it was modified to fit the system.

author: LoveLaika
author_rank: Frequent Contributor
timestamp: March 25, 2022, 02:52:16 pm
content: Well, I think I found theswitch. Turns out that my search parameters were wrong. Instead of fixed index stops, it was under continuous index stops. I guess it means that I can turn it continuously without stopping.Thanks for the help.