Need Help with Tektronix 500 series scopes - Page 1
Forum section: electronics / testgear

author: Aperna1985
author_rank: Contributor
timestamp: May 31, 2023, 02:03:09 pm
content: Hi everyone, I'm getting into tube radio and T repair and bought two used scopes for $50 one is a 531A and the other is a 536. When I then them on the fans run, the relay clicks and the CRTs light up, but I just get a Dot on the screen, I can move it around by playing with the controls but I don't get the line I'm supposed to have. Can anyone help me trouble shoot it? I already tested all the tubes and they test very strong, also both CRTs have been replaced. I think these came from a laboratory the insides are squeaky clean and they have calibration and maintenance dates written on stickers inside them.

author: AVGresponding
author_rank: Super Contributor
timestamp: May 31, 2023, 04:07:09 pm
content: 1. Do they have the plug-ins inserted?2. Are they set to X-Y mode?3. Are they set to External Sweep?

author: Aperna1985
author_rank: Contributor
timestamp: May 31, 2023, 08:25:49 pm
content: Ok the 531A has a Type CA plugin, which is inserted. I've tried cleaning the contacts and wiggling all the tubes. I tried turning the knob labeled triggering mode and it makes no difference between internal or external. If I turn the variable time knob I can make the dot wider, and the horizontal position knob moves the dot but that's it. I've attached a picture.The other scope is a 536, I'll correct my first post. That one has a dot that kind of shakes left to right. No matter how I adjust the Vernier position or the vertical position I always have the left arrow and the down arrow lit. If I switch to the 5x magnifier I get a little line that is biased to the left. If I turn the time all the way up or down the dot stops moving. You can see motion between 20 milliseconds and 5 milliseconds after that it just appears to sit still.The plugins in this one are type L and type 53/54T.

author: Arts
author_rank: Regular Contributor
timestamp: June 01, 2023, 02:05:44 am
content: Have you checked for missing tubes? Happens regularly with old Tek scopes

author: AVGresponding
author_rank: Super Contributor
timestamp: June 01, 2023, 08:53:09 am
content: Quote from: Aperna1985 on May 31, 2023, 08:25:49 pmNot the external trigger, the externalsweep

author: Aperna1985
author_rank: Contributor
timestamp: June 01, 2023, 11:23:13 am
content: Ok so the 531A turns on external sweep using the "Horizontal Display Switch" I have mine set to "Normal" which should be the internal sweep.I will double check on the 536

author: AVGresponding
author_rank: Super Contributor
timestamp: June 01, 2023, 04:00:43 pm
content: I'm far from an expert on this type of scope, however, I do know a couple of things, and have some more suggestions, now I can see pics.The red knobs should be set to the "Calibrated" position, where applicable. For the "Stability", turn it to "Preset". For the "Triggering Mode", set it to either DC or Auto.The "Trigger Slope" I would set to "Line" either + or -, which should trigger off the mains waveform the scope sees on its own psu, so should trigger even if the other trigger levels aren't set correctly. The "Time/CM" should be set to 5 or 10 milli sec, the "Horizontal Display" I would set to "Time Base".Have you any leads or probes? With the input ungrounded, with a lead or probe connected, you should see some 50Hz noise, with any luck.EDIT: I have paged Papa Smurf...

author: Aperna1985
author_rank: Contributor
timestamp: June 01, 2023, 04:31:25 pm
content: I got a hodgepodge of wires with it most have the BNC connector but I don't have a probe I didn't want to invest in it for knowing that I had something functional

author: TimFox
author_rank: Super Contributor
timestamp: June 01, 2023, 04:37:46 pm
content: Depending on the internal state (tube aging, etc.), you might have to adjust "Stability" manually to get a triggered sweep.As recommended above, you should start with "Preset" for the Stability setting.(This front panel adjustment went obsolete on later solid-state CROs.)When set to X-Y mode (X through the time base), can you deflect the spot with an external generator or front-panel calibrator output?

author: PwrElectronics
author_rank: Regular Contributor
timestamp: June 01, 2023, 10:17:20 pm
content: I am looking at the 531A since I am more familiar with that type (I have a earlier 531 (not A) version.Sweep speed is set to 5s/div. So, watch the dot there. Is it moving glacially slow left to right? Turn the sweep speed to a faster value (anything clockwise on that knob). Red knob triggering mode. Generally use automatic for most things.I don't see anything else that pops out that prevents getting a horizontal sweep line. Most likely issue is the sweep is so slow it looks like a slowly moving dot that would take 50 seconds to go left to right.

author: Martin.M
author_rank: Frequent Contributor
timestamp: June 11, 2023, 06:45:12 pm
content: before adjust anything please check first of all:PSU; the negative -150V. It must be exactly, there is apot for adjust that.All other voltages of the PSU use this -150V as reference, means, is the -150V wrong, all others will follow.Tired tubes can be found by swapping with another of same type, but put each tube back to it`s place bec. some of them are selected, so the swap can modify system acuracy.To identify a selected tube:When the first 3 Numbers are 154 it is not selected, is there a 157 it can be a selected single or pair.Martin

author: Aperna1985
author_rank: Contributor
timestamp: June 12, 2023, 09:45:55 am
content: Thank you, where can I check for the -150? I'm really not familiar with the inside of these scopes. I took all the tubes out and tested them 1 at a time on a tube tester, they actually all came back very strong. I was hoping for a weak tube.