Tek 468

[tek_n00b]

Hello
I bought a tek 468 on ebay that was being sold for parts and I'm trying to bring it back to life, when I turn on appears only a dot no trace. Made the measurement of voltages on the interface board and all are with the right value, but on the storage display board there is no voltage at the test points.
As there was no voltage on the storage I started by checking the storage power supply and bingo there was no voltage at the rectifier bridge because the fuses F4007 and F4009 were blown.
Prompt replace the fuses, turned on the scope and there he was working again, I was extremely happy and then discover that there is something still wrong with it.
Despite all the attempts I can not get a sharp trace, the best I could get is as shown in the picture a very fuzzy trace. And there are also problems at high frequencies speeds that makes the trace disappear or fade.

If someone can help me locate the cause of the problem I would be very grateful.
I appreciate all the help given.

https://www.youtube.com/watch?v=gQVsCYSZIbY

[ColinTheAmpMan1]

Hi tek_n00b,
At first guess, there is something amiss with the CRT supplies, but I had a similar problem with a 464 that I hadn't turned on for a while. Operating the "beam finder" a few times solved the poor focus. I'm not saying that this will work for your 'scope, but it's worth a go. I suspect that the contacts had oxidised a little in my case.
I believe that these 'scopes, while great when they work, can have problems due to the fact that the storage function sometimes fails and what with "unobtainium" ICs, they can be almost unrepairable unless you can find a scrapper with the correct good parts.
I thought this might be a good idea when I bought a 466 "for parts" to keep the 464 going, only to find that the CRTs are different!
I see that the trigger knobs for the "A" timebase are also missing, but those for the "B" timebase are present. I would be inclined, if you can't source some replacements, to swap them over, as the "A" timebase is used more than the "B".
Good Luck, Colin.

[dave cox]

Do you get a fuzzy trace with no input signal ?


One possibility is that a decoupling capacitor has failed. Tektronix liked to use tantalum capacitors (for their compact size and high performance) and these do sometimes fail suddenly - often resulting is a short circuit which could explain the opened fuses. I would take a quick look round of all the 'bead style' tantalums and look for a blackened one

dc

[maninashed]

As you are new to the forum, and you haven't said if you have any experience of working on oscilloscopes, Im not sure exactly how to approach this, but here goes.
Firstly, do you have the workshop manual? You will definitely need one for this, as it is one of the most complicated of all the 4XX series of 'scopes.
Having watched the Utube video, Im not sure that you know exactly how to operate a scope. When you are advancing the timebase control, your trace becomes a dot. This is happening at high scanning speeds. So the timebase is running intermittently. This can be due to dirty switch contacts, the knob can be loose on the shaft and its indicating wrongly, or there is a faulty component in the timebase selector circuit. Without more information it is impossible to say.
These 'scopes are not renowned for the sharpest of traces, and it is difficult to tell from a photo or video, if there is a fault of not.
Trouble shooting these begins with checking that ALL the psu voltages are correct in line with the manual, and that there is no excessive ripple. Failure or partial failure of the bridge rectifiers is common, also the smoothing capacitors are now well beyond their expected service life. So its imperative that you check for ripple on the supplies before you start digging any deeper looking for faults.
Bill