How to repair Tektronix 465B trigger slope switches  - Page 1
Forum section: electronics / repair

author: Bill K
author_rank: Newbie
timestamp: May 27, 2022, 11:22:50 pm
content: Hi All,I haven't found a thread with instructions for repairing the +/- trigger slope switches that seem to be damaged on most Tek 465B scopes, so I'll post what has worked (twice) for me. These are Tek part # 311-1192-00This part is a 10k pot with a co-axial switch shaft. The inner shaft and the rather delicate switch is easily damaged by bumping the slope knob which can render the switch non-functional. I see a design flaw here as there is no support between the outer sync level knob and the inner slope knob.Here's what the switch looks like. This photo was taken after the repair was completed.The first step in repairing the switch is to cut the large tab that's at the 6 o-clock position in the above photo where it intersects the switch case. This is best done by filing off the corner. Then carefully bend up the other three tabs that retain the fiber disk at the back of the switch. Note DO NOT drill out the rivet. Ask me how I know!Here's what you'll see when you carefully pop the back off the switch.There is a very small spring contact that shorts the two pins when the switch is closed. It actually contacts the sides of the contacts rather than the tops. This spring is not in the photo above because it has fallen out on the bench!The failure mode of the switch is 1) corroded contacts - clean the contacts and the spring I mentioned above with contact cleaner and a brush. 2) inward pressure on the switch shaft has bent the shaft bearing in the switch case and the tiny lever that toggles the switch plate back and forth. Apply pressure to the case as shown below to take up the excess movement of the shaft and very carefully bend the lever away from the fiber disk so that the lever will fully engage with the little finger that's connected to the shaft. If you feel like it, place a small amount of grease on the lever fingers.Reassembly is tricky! Play with the mechanism that's attached to the switch fiber disk so that you understand how it works. There's a torsion spring that work with the part I'm calling the lever to provide the snap toggle action. I spent some time wondering how I was going to get this all back together since the lever needs to be centered when the fiber disk is placed on the back of the switch and centered is the one place that the lever does not want to be (due to the force of the spring). I eventually came up with the idea of drilling a hole through the back of the switch and the switch plate and using a pin to hold everything in the right position for assembly. I used a #60 drill in the dremel.The image above shows everything lined up for assembly. The drill bit is now the pin holding everything in the centered position. The spring is exerting pressure against the pin. You can also see the two fingers of the spring contact poking up through the switch plate.You can now carefully lower the switch assembly into the housing. You'll need to play with the switch shaft while assembling to get the finger to engage properly with the lever.Once the back of the switch is sitting properly on the housing hold the back down and remove the pin. Try operating the shaft. You're hoping to get a nice snap action. Don't feel bad if it takes a few assemble/disassemble cycles. If the action is good test the switch electrically. If everything is good electrically and mechanically then operate the switch about thirty more times to make sure that nothing fails. Then you can bend the three tabs back and reinstall the control.

author: t1d
author_rank: Super Contributor
timestamp: May 28, 2022, 07:52:10 am
content: Excellent repair! Kudos! You might change you title to "How to Repair Tektronix 465B trigger slope switches," so folks know that you are posting the solution, not a question.

author: Bill K
author_rank: Newbie
timestamp: May 28, 2022, 11:39:24 am
content: Quote from: t1d on May 28, 2022, 07:52:10 amGood idea, and done!-=BK