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Tektronix 2235 repair thread

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Shock:
Regarding power supply noise, doesn't say specific to 2235a but there is this service note.

http://www.hakanh.com/dl/docs/hardtofind/2200_ps_noise.pdf

bd139:
Power supply noise is normal on these.  Usually goes away after a few minutes. Or the power supply explodes  :-DD


--- Quote from: paronaram on December 21, 2019, 06:38:40 am ---Removed scope tube (very easy BTW), and guess what, pin is there, it's just cable was not connected. Looks like someone was trying to troubleshoot already.
So I reconnected both cable from PCB to Horizontal pins, start the scope, and same issue... Well something should start working, cable was completely disconnected from that pin.
On the internet I saw a video were guy was troubleshooting unrelated issue on the same Tek, and he was talking about pots on the top PCB (see picture), I move this pots around about 20 times, and turn the scope back On. See last two pictures ... very unstable but I see A and B now!

But Horizontal sweep still not there 
When I press beam finder dot gets in the area when I don't see signal at all, so tube is capable to display something there

--- End quote ---

That’s good news then.

Next steps are:

1. Check power supply voltages
2. Stick it in X-Y mode and inject a signal into X and see if that works.
3. If it doesn’t then signal trace that through the amplifier stages until you find the bit that stops making sense.

H713:
Hello, I just purchased a Tek 2235 off university surplus with what seems like a similar issue. No trace, however when I push the beam find button, I get some part of a trace that sweeps appropriately with the time base setting. I can also move it up/down and left/right with the X and Y position controls (though with limited movement). When I feed a signal (random sine wave in this case), there is still no trace, however I can see some part of the signal displayed when I push the beam find button. I measured the power supply rails, (or at least the test points on the board) and they all seem to be in spec, so I'm inclined to say that it is not a power supply issue.

Both channels behave exactly the same, so I don't necessarily expect it to be the vertical amplifiers (they'd have to have both failed in the same way). In my case, I've got other scopes that I can use to troubleshoot this one. Some direction on where to start looking, however, would be welcome.

paronaram:
That beam finder button maybe faulty ... ?
If its affecting both channels

floobydust:
I can't see your trigger section buttons. In Auto sweep, a trigger is not needed and the sweep generator does the work.
It might be triggering/sweeping fine but the position is way off (beam finder reigns it in).  Beam finder also cranks the intensity.
Looking at the Tek service procedure, check first for a Z-axis unblanking signal at TP482, then sweep sawtooth at R707, then H-deflection plates having 40Vpp sawtooth.

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