TEK 434 Oscilloscope Repair

Discussion in 'General Electronics Discussion' started by Newphys, Aug 9, 2018.

  1. Newphys

    Newphys

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    I am completing the repair of this scope - very hard to fix compared to the 500 series.
    Does anyone know the orientation of the two 3-pin plugs on the CH1 and CH2 diode 'switching' push button board?
    I forgot to take a picture while it was upside down, so I dare not turn on power until I know I did this right.

    The result would be major damage, I would guess. One really dead 434.

    The official early or late TEK 434 manual does not tell me this.

    I can post a photo if needed..
    Newphys
     
    Newphys, Aug 9, 2018
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  2. Newphys

    Cannonball

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    A photo and a schematic would help.
     
    Cannonball, Aug 9, 2018
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  3. Newphys

    Newphys

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    Thank you for your quick response!
    My TEK 434 Serial # is B151227. Since I posted, I learned a bit more from page 3-8 of the early TEK manual on this scope. I can signal trace (no power) with an Digital ohmmeter.
    I will need to post photos and Diode gate schematic (page 3-8 TEK 434 - early pdf) after I learn the limits of your file upload options. My camera files are approx 8 Mb, but much smaller (pinhole) cell phone photos are not currently acceptable.

    Thanks, Newphys
     
    Last edited by a moderator: Aug 11, 2018
    Newphys, Aug 10, 2018
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  4. Newphys

    Newphys

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    Cannonball - Thank you! Apologies for my attempts to reply on this site.
    Max size of uploadable digital camera photos still unknown - photo pending. 8 MB ok?

    I will also need to replace a CH1 TEK 'only' part:
    -- U210 # 153-0050-00 Preamp linear IC. Cost unknown.

    Page 3-8 of the early TEK 434 manual gives me a schematic which I can use to signal trace the slow way with a D.V. - Ohmmeter - unplugged and powered off!!
    Newphys
     
    Newphys, Aug 10, 2018
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  5. Newphys

    Newphys

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    DSCN3249.JPG DSCN3251.JPG
     

    Attached Files:

    Last edited by a moderator: Aug 11, 2018
    Newphys, Aug 11, 2018
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  6. Newphys

    Newphys

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    Sorry about the Quote noise Unquote!
    Here are the above photos of the 434 scope in repair, showing the two 3 pin plugs, orientation unknown. I'm about to trace the diode bridge circuit -- unpowered - with a digital voltmeter.. I just need to find R427, and R 429..
     
    Newphys, Aug 11, 2018
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  7. Newphys

    Cannonball

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    I am sorry, it looks like you will need to slow trace to be on the safe side. R 427 from the schematic goes from a connection on the ch1 switch. R429 goes from a contact on the ch2 switch.

    I wish I could be more help. Let me know how this turns out.

    Cannonball.
     
    Cannonball, Aug 11, 2018
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  8. Newphys

    Newphys

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    Thank you. I don' t understand your answer about a trace, unless your mean slow down my circuit tracing before turning on power. All I need to do is plug in these two connectors - either upside up or upside down. I already know about R427 and R429, but not where they physically are inside the scope.

    This lightweight TEK434 certainly is not one of TEK's best - unlike my pictured fully restored and calibrated 200 MHz TEK 585a with type 82 plugin (50 ohms termination). Unpictured is my fully restored 150 MHz (+) TEK 454, chosen because it has no proprietary IC's.

    Next project is restoring the 1 Ghz TEK 7104. Scary!!

    Pardon my pun, but I would just be happy getting a warmup CRT 'trace' on the 7104!! This is a thoroughbred hybrid digital/analog device. .. I do know computers and digital better than tubes..

    I am still not clear on how BNC cables can work at 1 GHz, but that is another issue involving TDR etc, etc. I had thought I would need SMA or similar...

    My 35GHz tube work in 1973 is very rusty.. Nearly got killed by a magnetically levitated TEK 555 that year.
    It died, I didn't. Took me 7 months to restore another 555 - into full glory...

    This 434 is a much less valuable 'dry run' with these 'blankety blank' pushbuttons having 1mm x 4mm microminiature pins that fall out! Hopefully the TEK7104 is less trouble...

    Thanks for all your help.. I will let you know how I do with the TEK 434. It might take a week or longer...I have learned over the years to slow down before blowing things up!! Best way is several projects, so you can sleep between steps. Patience is a virtue that our current US president does not seem to understand..
     
    Newphys, Aug 12, 2018
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  9. Newphys

    Cannonball

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    Good Luck!
     
    Cannonball, Aug 13, 2018
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  10. Newphys

    Newphys

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    Cannonball – I have repaired much of the TEK 434, but am now unable to get traces from both channels one and two.. Channel 2 LED display still lights up like before the repair..
    Don't know about the two Tek linear IC's post the two attenuator circuits. ..

    During the repair I discovered several subtly cracked epoxy boards, apparently still with retained electrical connections... The store/flash options still work -- but I don't need/want these..

    Review of the early TEK manual routine repair/maintenance checklist has not been much help, as of yet...
    All LV DC voltages check out, except the -75v, which is -61 V DC. Can't check HV over 1 KV with my DVM - only with a VTVM or scope...

    Regarding preparation for my pending repair of the 1 GHz TEK 7104,
    I'm not impressed with the TEK engineering of this time era....

    My fully restored TEK 454 - containing no integrated circuits -- works very well up to 200 MHz into 50 ohms. Likewise my pictured and restored 'boat anchor' TEK 585a with type 82 plugin.. Good to 40 microvolts with a 1A1 plugin, and 81a adapter..

    Newphys
     
    Newphys, Aug 14, 2018
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  11. Newphys

    Newphys

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    I can add one more item -- Using a differential probe approach on the CRT vertical, I was able to determine that the 434 Channel 2 vertical still works, as well as the storage feature. The scope trace still does not work, but since I know the CRT is good, that should be an easy fix.
    The pushbutton repair lock still works, which does give me more confidence to tackle the TEK 7104 repair..This epoxy board problem with the 434 may make repair of this scope a constant headache - likely not worth it just for the storage feature, highly questionable in this modern digital camera era.

    Do all TEK 434 scopes have this epoxyboard cracking defect?
    Newphys
     
    Newphys, Aug 16, 2018
    #11
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