need help removing rotary switch on Triplett 630 Type 4 - Page 1
Forum section: electronics / testgear

author: zumzar
author_rank: Newbie
timestamp: August 11, 2025, 11:44:15 pm
content: Hi, I got this 630 long time ago from a good friend and finally have some free time to look into it. DC ranges are spot on, but some of ohm meter ranges are not responding. The corresponding resistors on the wheel check out correctly and further tests show that the rotary 4-wafer switch is not making some contacts. Spraying contact cleaner through the narrow opening and tuning the switch for a few minutes did not resolve the issue.The meter is not showing any battery leak damage, but it stayed in humid NYC climate for decades, which may have contributed to wafer switch problems.Unfortunately, 630 type 4 has the entire switch enclosed in a black bakelite barrel, so I have to remove the barrel with the switch in order to clean it. To do that, I will have to detach the red selector knob on the front, I suspect there might be a nut and a washer underneath it that will release the wafer barrel assembly. I think that the knob is just press fitted onto a profiled/splined metal shaft of the wafer switch, since I don't see any screws that hold it. I tried to pull the knob out by hand, then used some dental floss to make a loop around it and pull, but it is not budging. I am hesitant to use any metal pliers because it can damage that beautiful red and black bakelite.Has anyone successfully removed the selector knob and the wafer switch assembly on these meters? I would rather take you advice than damage this nice meter.thanks,Vlad

author: Oilngas
author_rank: Contributor
timestamp: August 12, 2025, 02:31:13 am
content: I have removed the selector knob from a 630 by first applying many protective layers of masking tape to the knob and using pliers. It takes a strong pull, but it came off without damaging the bakelite.

author: zumzar
author_rank: Newbie
timestamp: August 12, 2025, 10:28:47 am
content: Thank you for your input.I was contemplating this approach, but decided to get a second opinion from someone who has actually done it.I am planing to use a thick 3M duct tape and lock pliers. I have to be careful with the amount of pressure I apply on the pliers not to crack the bakelite knob.

author: zumzar
author_rank: Newbie
timestamp: August 12, 2025, 10:49:11 am
content: Wise grips did it! Thank you!

author: Stray Electron
author_rank: Super Contributor
timestamp: August 12, 2025, 01:59:07 pm
content: I was going to say that some knobs used set screws to hold them on, and in some cases I have seen two set screws installed. One behind the other. the 2nd set screw prevents the first one loosening up and the knob coming off accidentally. So keep that in mind when dealing with set screws.I have a Simpson 261 laying in front of me right now and it uses a set screw in all three knobs. But I don't know if they're doubled up or not.

author: Oilngas
author_rank: Contributor
timestamp: August 12, 2025, 04:35:45 pm
content: Be careful of a possible shock hazard if you encounter those "double" set screws. My Simpson 460-2 has the following warning in its manual..."...the shafts of the function and range switches are connected to the common input terminal. The shafts are insulated from the user by the knob design and by having the fastening set screws below the knob surface. As an added precaution, each fastening set screw (metal) is covered by a nylon set screw."

author: zumzar
author_rank: Newbie
timestamp: August 12, 2025, 04:56:33 pm
content: Just to report an update - I removed the fuse contact and ohm variable resistor to be able to lift the switch barrel. It is easy because everything is bolted to the chassis with top quality SS fasteners and brass thread inserts. Then I removed the wafer switch together with the barrel by unscrewing the slotted nut from the front. Removed the back plate on the barrel that is held with 3 long bolts. It revealed the spring loader 'clicker' with two arms holding the teethed wheel attached to a '+' profiled shaft running through all four wafer sliders. I CAREFULLY pulled the shaft out so position of wafer sliders was not disturbed. Then I sprayed contact cleaner (kontakt 61 is european deoxit of choice), replaced the shaft back and rotated it several full turns. I repeated the contact cleaner application several times, combined with shaft spinning.I assembled the meter and could see some improvement - all ranges were back, but some of them still not stable. I disassembled and reapplied the contact cleaner a few more times. I wish I could just dunk the whole wafer barrel into a bath of contact cleaner and leave it overnight. Disassembling the barrel sections does not seem to be a good idea, since all resistors would need to be desoldered. It was obvious that designers of this meter made it so the entire barrel would need to be replaced as a single component. Was this an iphone of the '70s?Obviously, it will take some time and quite a bit of a 'massage' to get this wafer switch back close to 100% reliability, where it should be. Again, I don't see any signs of battery leak damage, so this is really result of normal use in somewhat higher humidity, which can obviously penetrate the quarter inch barrel between the ring sections separating static part of the wafer. Worse, the barrel might have made it more difficult to release the accumulated humidity. Too bad that otherwise good instrument using top quality materials and components was made unserviceable by a dubious design decision to obscure the wafer switch. I am also not impressed with the design decision to have batteries unprotected right above the wafer switch and precision resistors, unless they were making leak proof batteries back in the '70s. if you have this meter, it is certainly worth developing a habit to store it horizontally.