# Help me fix my Tektronix 485 'scope!! **URL:** \ **Category:** Factual Questions\ **Created:** [March 7, 2003, 6:35am UTC](https://boards.straightdope.com/t/help-me-fix-my-tektronix-485-scope/159676 "2003-03-07T06:35:46Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [March 7, 2003, 6:35am UTC](https://boards.straightdope.com/t/help-me-fix-my-tektronix-485-scope/159676/1 "2003-03-07T06:35:46Z")
I have a Tektronix 485 oscilloscope that needs a new power supply assembly. AFAIK, that’s the only problem with the unit. Does anyone know where I can get this part cheaply? I’d repair the board, but the critical parts all have Tektronix proprietary numbers, so I have no idea where to begin. It looks as though someone attempted a repair, but the soldering is so poor, I can only assume they totally screwed it up. Help! ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [March 7, 2003, 7:01am UTC](https://boards.straightdope.com/t/help-me-fix-my-tektronix-485-scope/159676/2 "2003-03-07T07:01:26Z")
You can get this unit on Ebay [Tektronix 485 350MHz Oscilloscope](http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2513287378&category=4677) Depending on price it might be cheaper to part out the old unit and use it’s PS. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [March 7, 2003, 1:45pm UTC](https://boards.straightdope.com/t/help-me-fix-my-tektronix-485-scope/159676/3 "2003-03-07T13:45:47Z")
Do you have a schematic? I’ve never seen a power supply board for a scope, but I can’t fathom why most of the parts can’t be replaced with generic components. Is it a linear or switching supply? What’s wrong with it? Did you lose a rail? Is it blowing a fuse? Too much noise or ripple? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [March 7, 2003, 1:54pm UTC](https://boards.straightdope.com/t/help-me-fix-my-tektronix-485-scope/159676/4 "2003-03-07T13:54:36Z")
It’s a switching power supply. The main problem is it isn’t switching, and I suspect the one or both of the two large chopper transistors on the board. However, as I said they are marked with Tektronix proprietary numbers and cannot be cross-referenced. A schematic would be helpful, unfortunately I have been unsucessful in locating one, and the service manual for this scope is Quite Expensive. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [March 7, 2003, 2:05pm UTC](https://boards.straightdope.com/t/help-me-fix-my-tektronix-485-scope/159676/5 "2003-03-07T14:05:37Z")
I think you’re on the right track; when a switcher dies it can usually be traced to a blown transistor. Can you tell if it’s a FET or bipolar? If it’s a new scope I would suspect a FET. At any rate, it can be easily determined by the biasing arrangement. What’s the number on the transistor? Perhaps I could help. Worse comes to worse, you can just try replacing it with (what we believe would be) a close match. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [March 7, 2003, 2:19pm UTC](https://boards.straightdope.com/t/help-me-fix-my-tektronix-485-scope/159676/6 "2003-03-07T14:19:26Z")
This scope was originally manufactured in the 70’s. This assembly is marked “Copyright 1070 Tektronix”. the two transistors in question are marked 151-0368-00. They have the Motorola “M” logo on them, but Motorola is of no help either. I’d really prefer to replace the whole assembly, since as I said, someone attempted a previous repair and really butchered the job. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [March 7, 2003, 2:21pm UTC](https://boards.straightdope.com/t/help-me-fix-my-tektronix-485-scope/159676/7 "2003-03-07T14:21:13Z")
That should read “1970”. I’d be impressed it had been made in 1070! :eek: