Chopped and Interrupted lines on Tektronix 2213 Oscilloscope - Page 1
Forum section: electronics / repair

author: karlseN
author_rank: Newbie
timestamp: December 26, 2023, 01:58:54 am
content: Hello! I’m new here and i’ve got a question regarding my Tektronix 2213 Oscilloscope. Whenever I look at signals on my scope, the traces appear chopped or sometimes even interrupted. I can’t figure out what the problem could be since everything else works fine. The only other thing to mention is, that at higher timebase settings the traced get really dark. I can berely make anything out on the screen even on maximum intensity. Any help would be greatly appreciated! Thanks in Advance!Ps: volts per devision setting doesn’t change anything.Merry Christmas to everyone,Karl

author: macboy
author_rank: Super Contributor
timestamp: December 27, 2023, 04:28:35 am
content: Post a photo of the front panel to go with the screen photo so we can see what settings you are using. Otherwise anything is just a guess.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: December 27, 2023, 05:43:45 am
content: At first, this looks like noise. I had a similar problem with noise in my waveform on my Tek 2235. Replacing caps fixed this.Also, it looks like possibly the Z-Axis amplifier is slow in this one because of trace dimming at high speeds. This is only a guess however.As the saying goes, Thou Shall Check Voltages.

author: CaptDon
author_rank: Super Contributor
timestamp: December 27, 2023, 05:33:30 pm
content: Ummm, are you in the CHOP mode and not in the ALT or single channel mode?

author: karlseN
author_rank: Newbie
timestamp: December 27, 2023, 09:56:00 pm
content: Hello everyone! First of all, I want to thank you all for giving me points to start troubleshooting from. I am using the scope in Alt mode. Switching to chop mode changed nothing. I am going to start checking caps. I think that’s a good point to start from. I have attached two Images containing the front panel configuration and a closeup image from a 100 kHZ sine wave generated by my function generator. In the picture of the Sinewave you can see, that the return trace of the electron beam is visible. Could that be another hint to a faulty Z-Axis Amplifier?Thanks again!Karl

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: December 27, 2023, 10:55:50 pm
content: Quote from: karlseN on December 27, 2023, 09:56:00 pmYes! That is a clear sign that the Z-axis amplifier is slow! So my assumption was correct. To troubleshoot this, you need another oscilloscope to probe the waveforms of the blanking signal. Start from where the signal is generated, and keep following it to the control grid, until the waveform becomes "slow" or it starts to significantly round off.Edit: Also check the power rails anyway. It is possible the Z-axis amp is not getting enough voltage. If you have an analouge volt meter, set it to AC and measure the AC RMS of the power supplies. Most analouge volt meters are accurate up to at least 500kHz.

author: CaptDon
author_rank: Super Contributor
timestamp: December 27, 2023, 11:00:50 pm
content: Could also be a symptom of excess brightness (turning up the intensity to far) or a mis-adjustment internally to what ever they call the control that sets the beam limiter or beam blanking. The 2213 wasn't exactly a top-of-the-line scope. It does have some limitations and make sure the C.R.T. filament overvoltage correction was completed! They fixed the issue after a certain serial number.

author: CaptDon
author_rank: Super Contributor
timestamp: December 27, 2023, 11:05:33 pm
content: Follow to the crt control grid? isn't that at like about -1100vdc?? Might not be a place where a newbie should be 'scoping'. Dim trace at fast sweep speeds kind of just goes with the analog scope territory?

author: karlseN
author_rank: Newbie
timestamp: December 27, 2023, 11:12:15 pm
content: Wow thanks for the swift response! I have asked a buddy of mine to borrow his oscilloscope for tomorrow. I will look into the Z-Axis slowness tomorrow with his scope! I will also check if my scope has the Grid overvoltage protection. Mine has the serial number 206639. It already had the revised power supply section in it…

author: MathWizard
author_rank: Super Contributor
timestamp: December 28, 2023, 09:21:11 am
content: Quote from: BlownUpCapacitor on December 27, 2023, 10:55:50 pmTektronix mmanuals are good for having waveform pictures too, albeit small black and white pictures aren't the best.

author: karlseN
author_rank: Newbie
timestamp: December 30, 2023, 07:23:40 pm
content: I just wanted to post a quick update regarding my 2213... The last two days were spent completely with mesuring and probing arround the scopes Z-Axis Amplifier. I have finally found the fault and I have successfully fixed it. The culprit was C865. The charge on this capacitor determines the CRT Grid bias. Furthermore this 3000V 20nF Cap is used by the CRT blanking circuit. In hindsight it makes this capacitor the cause of many problems on the Scope. Oh and i have also started replacing electrolytic caps on the board. I can already see a reduction in the noise on the CRT!I have attached a portion of the Z Axis circuit, where it s quite obvious that C865 causes a lot of issues;)Thank you all once again for helping me! I wish you all a happy and healthy 2024!Karl from Germany