Tektronix 485 Vertical Section and Trigger Tech Argues with Scope, Scope Almost Wins

[@erin19030]

Nothing beats an analogue scope. I have an original Tektronics made for IBM field scope. It was designed to fit under an airline seat and was within carry on weight. It was part of my severance package many years ago. I use it as a pair of eyes into circuitry, for troubleshooting. Exact measuring is not in my scope of performances although I do keep it calibrated to general specs.the are some functions I never use. Dual trace is nice to have but most of the time a single trace will do. My needs are simple doing audio and AM restoration. I do like it’s portability to take it from one bench or location to another.

[@ebayscopeman]

When triggering internal you need to move the B trigger switch to internal Not B Runs After Delay. When you go to intensified mode when it is set to the top B Runs after delay the sweep just runs, the B trigger is disconnected. To check this set the switch to B Runs After Delay (Apply a 10KHz Sine to Channel 1 and select 1mS/div on A Sweep and 100uS/Div on B sweep) and select Intensified mode, then rotate the Delay Time Position. You will see the intensified portion move smoothly through the A Sweep. Now change the B to INT trigger and adjust the B level to trigger the B sweep. Moving the Delay Time Position knob you should see the intensifed portion move in steps from wave to wave as it triggers. Note that with B Runs After Delay the B sweep does not even have to trigger. On my 485 the B sweep was not triggering. This test is how I found out that the Tunnel Diode of the B sweep was bad. Fortunately like you I had a donor scope. Also your comment on the power supply: Tek did use hermitically sealed Tantalum caps and Electrolytics in these scopes as standard as a mix. The ones that were a problem were the epoxy dipped ones. They often fail short, The reason is many of those caps were used right at their voltage ratings I.E. a 22uF 15V used on a 15V power supply. My scope had two dead shorted ones when I bought it broken this past Sunday at a hamfest. It also had two bad transistors (one in the supply and the pill packaged one in the B trigger) as well as a bad TD. The Trigger adjustments are finickky on this scope and I had to slightly retouch Arm and Out after using the procedure to get it to trigger correctly. Still even today a great instrument! Sam W3OHM

[@Sigmatechnica]

I often wonder if there is any benefit to a 7000 series owner to also own one of these. suppose they are a bit more compact...

[@ZenwizardStudios]

One slight one actually. The switchable input. In the 7k series to go from 1 Meg to 50 Ohms requires a plugin change. Also on the 485 the 1meg input at 250Mhz is "slightly" better speced. If I recall correctly the 7A26 tops out at 200 Mhz to get the 400, 500, and 1Ghz, bandwidths these are all 50 Ohms. The 485 also has the slight edge on XY bandwidth as well. I believe the 7K frames horizontal bandwidth is around 6Mhz. So in the grand scheme of things probably not. But there are some edge cases where the 485 squeaks out a bit better performance. But it defiantly wins in the portability department.

[@Sigmatechnica]

@@ZenwizardStudios aah yes good points. Not enough for me to justify aquiring one though i think.

[@jenniferwhitewolf3784]

I can guarantee those 'proud' set-screws are not original. You are correct.. someone else put them in. Tek absolutely used flush fitting screws. I have used those couplers for decades, originally from the Tek country store in the late 60s into the early 70s,, and later from assorted surplus sales outfits.