EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: py5pa on March 09, 2017, 09:20:28 pm
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When I turn on the equipment, the image of the photo appears. I have to dial a / b to continue. The oscilloscope works, but without the readings. Any ideas for solving the problem?
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First the 4 rows of 1s "indicate" scope readout circuit problem and the diagonal trace could be something else.
Regardless , download the smaller file service manual here:Wait for the words to change before clicking. ;)
20Mb file:
http://elektrotanya.com/tektronix_2445b_2455b_sm.pdf/download.html (http://elektrotanya.com/tektronix_2445b_2455b_sm.pdf/download.html)
The user instruction manual: Although it's A vwersion should be simi8lar to a B?
2445a user manual
http://www-3.unipv.it/lde/strumentazione_strum_banco/oscilloscopio.pdf (http://www-3.unipv.it/lde/strumentazione_strum_banco/oscilloscopio.pdf)
This is an old instrument so capacitor replacement is required like here:
http://bradthx.blogspot.sg/2014/01/tektronix-2445b-capacitor-replacement.html (http://bradthx.blogspot.sg/2014/01/tektronix-2445b-capacitor-replacement.html)
Teardown photos :
https://www.eevblog.com/forum/testgear/tektronix-2445-teardown-pictures/ (https://www.eevblog.com/forum/testgear/tektronix-2445-teardown-pictures/)
Since this is 200 Mhz. scope worth to repair. :box:
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Thank you very much, I will replace the capacitors and see the problem is solved.
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First, I would get a proper service manual and for the correct model. Although they are similar, there are differences between A, B, and non-A/B versions. If you haven't worked on these scopes it can get confusing if you're not looking at the right manual.
Unfortunately, the manual on elektrotanya.com is incomplete. It does not have schematics or placement diagrams. I wasn't able to locate one with schematics anywhere for you. However, you can buy a high quality scan from Artek:
http://artekmanuals.com/manuals/tektronix-manuals/ (http://artekmanuals.com/manuals/tektronix-manuals/)
I've purchased manuals from them before; they are top notch.
There are differing opinions, but I would not run out and start replacing components without at least doing some basic troubleshooting. Wholesale component replacement, depending on your skill level, can sometimes make the situation much worse by compounding re-assembly errors with the original problem.
If you buy the service manual, there will be troubleshooting flowcharts that start with checking the power supply voltage levels and ripple. If you have a DMM or other working scope this should be easy. If you say this scope works after you press A/B, you might even be able to use it on itself for the simpler tests.
Do a visual inspection. Look for capacitors that looks obviously bad, such as leaking or bulged. Try gently pushing on connectors or reseating them. I'd pay particular attention to the A5 control board, which is on the right-hand side.
You should also try to get into the diagnostic routines to see if they report anything interesting. The information on how to do it is included in the elektrotanya.com manual in the maintenance section. It may not work given the issue you're seeing with the display, but it's worth a try.
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First, I would get a proper service manual and for the correct model. Although they are similar, there are differences between A, B, and non-A/B versions. If you haven't worked on these scopes it can get confusing if you're not looking at the right manual.
Unfortunately, the manual on elektrotanya.com is incomplete. It does not have schematics or placement diagrams. I wasn't able to locate one with schematics anywhere for you.
If all else fails look at the 2465B manual (http://www.wild-pc.co.uk/docs/Tektronix-2465B-service.pdf), the 2465B and 2445B are almost identical apart from some minor differences in the delay line drive and final Y amplifier which limit the bandwidth in the 2445B
However, you can buy a high quality scan from Artek:
http://artekmanuals.com/manuals/tektronix-manuals/ (http://artekmanuals.com/manuals/tektronix-manuals/)
I've purchased manuals from them before; they are top notch.
+1 for Artek :)
There are differing opinions, but I would not run out and start replacing components without at least doing some basic troubleshooting. Wholesale component replacement, depending on your skill level, can sometimes make the situation much worse by compounding re-assembly errors with the original problem.
Except that the 24[46]5B is the one which is notorious for leaky SMD capacitors on the A5 processor board which can easily destroy traces and make a significant mess of the PCB - looking at the CRT I would check the PSU voltages for being in spec then head straight to the A5 board and check things out. Even if there are no problems I would swap those caps (google "Tek 2465B leaky capacitors" for more details)
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Thank you very much for the answers. I have other oscilloscopes and I have already done some tests. All the voltages are ok. The initial waveforms starting from the 10 MHz clock are also. I am not adept at leaving replacing parts, but I will replace the smd electrolytic capacitors of the board A5, it seems that they are problematic with the time. I am using the 2465B scheme which is very similar, since I could not get the original from my equipment. I'll check Artek's if it's the right one for my model.