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Thread: Tektronix 4041 Thermal Printer repair - may also work on AIM-65 thermal printer

  1. #1

    Default Tektronix 4041 Thermal Printer repair - may also work on AIM-65 thermal printer

    With my success on recovering all the Tektronix 4041 GPIB Controller System Verification tape files, and repairing NOS 3M DC100A tapes with dehydration, I decided to see if I could repair the two inch thermal printer in my 4041.

    The printer would print dots, after carefully removing the printer from the 4041 and cleaning the print head with 91% Isopropyl Alcohol on a cotton swab, but the output was unrecognizable.

    After my repair - you can see in the photo the bad printout from before the repair and the good printout after the successful repair!

    Step one was internet research looking for the Tektronix 4041 service manual (I couldn't find it).
    Next remove the printer looking for a part number - found PU-1800, then search for that part number - and I got a hit on an EBAY auction for PU1800 repair, which also listed AIM-65.

    The EBAY auction description indicated the seller repairs these printers from a small stock of printers of this type. Although it appears that there are different printers in the series, different input voltage and different timing disks.

    I decided to see if it was something simple - like a dirty timing disk.

    First photo shows top of the printer in the 4041 after carefully pulling the top cover back several inches.

    Remove the three screws and aluminum brace (be sure to catch the nut under the right screw so it doesn't fall into the case). The left screw is tapped into an aluminum plate (no nut) and the middle screw is tapped into the plastic printer cover.
    Then you can remove the thermal paper, and remove the plastic cover over the printer by sliding it to the left and toward the rear of the 4041.

    Now the printer is exposed and you can remove the screw in the center of the white timing disk cover:

    I wasn't sure what was on the other side of the timing cover - so I went to a lot of effort to remove the printer, after pulling off the entire front panel.
    *** You don't need to do that ***.

    Here is a photo of the printer removed completely from the 4041:

    Tektronix mounts the printer upside down from how it is mounted in the AIM-65, so that the printer paper coils up, and they put a paper tear bar on the front panel to tear off the paper on top of where the paper comes out.

    Note the timing cover 'arm' with notches at the front edge. It is actually sitting on some hard putty. I couldn't see that while it was installed in the 4041.
    This means you can simply remove the cover, do the repair, then put the cover back into the putty - and the timing gear will be back in the original position.

    Here is the timing disk and timing contacts in the timing cover with the cover removed:

    It looked pretty clean - but I wondered if the grease installed at the factory had hardened over 40 years might be the problem.

    I used 91% Isopropyl alcohol on a cotton swab and carefully wiped the contacts with one end, and the timing disk with the other end of the swab.
    Both ends of the swab had grease and looked dirty (blackened).

    I then used a dry cotton swab to wipe off the contacts and the timing disk and reassembled.

    Here is the printer test from the System Verification tape - printer is repaired!

    I wonder what kind of grease I should put back on the timing disk?

    This repair might also fix an AIM-65 printer!
    Last edited by nikola-wan; June 6th, 2020 at 09:01 AM.

  2. #2


    Checking the internet for slip-ring grease - it looks like I should use a silicone dielectric grease. I've got a small tube of "Super Lube" silicone dielectric grease that I bought for greasing the lead-screws in my 3D printers.
    I'll try the Super Lube on my 4041 printer timing disk.

  3. #3
    Join Date
    Feb 2009
    Southern California, USA


    An excellent well documented article on these thermal printers. Thanks so much.

  4. #4


    Quote Originally Posted by dave_m View Post
    An excellent well documented article on these thermal printers. Thanks so much.

    I put a little Super Lube silicone grease on the timing wheel today and think I still have good alignment:


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