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26-4152 12 Meg Disk System Restoration

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    26-4152 12 Meg Disk System Restoration

    I picked up a 26-4152 12 Meg Disk System a while ago and decided to see if I could get it working. I love the modern solid state storage solutions like FreHD, LoTech and MISE for the various flavors of TRS-80, but I really wanted an authentic hard drive solution. Also, since I am trying to create a TRSDOS-16 environment with my Model 16, none of the modern storage solutions are applicable so I really don't have a choice.

    IMG_0964.jpg
    Radio Shack 26-4152 12 Meg Disk System

    Since I could not even hear the disk spin at power on, I knew there were some issues with the unit. I proceeded to open her up.

    If you are familiar with this device, you know that it uses the Type 2 8x300 controller. This controller is not as trouble free as the later Type 3 WD1010 controller. Luckily I did have the 5 Meg drive service manual which applies to the 12 Meg unit since they share the same internals other than the actual drive unit itself. Some people refer to the actual drive as "the bubble", but I just have a difficult time using that term for some reason. It seems so silly, but it is concise.

    My first suspect was the power supply. The 26-4152 uses the same power supply as the Model 4. It was not outputting the proper voltages. Now, I have had terrible luck with these power supplies lately. Finding a replacement is difficult and when you do find one, well, good luck if it really works properly.

    I decided to try using the MeanWell RQ-125D as a PSU. Others on this forum have used this unit successfully in the Model 2 so I knew it would be more than adequate for this hard drive system. The RQ-125D is actually very close in dimensions to the original power supply, so the fitment was no problem. And it outputs nice clean +12VCD and +5VDC just like the original.

    IMG_0958.jpg
    The RQ-125D PSU mounted next to the ST-251 hard drive

    I next discovered that the original Tandon TM-603 12MB hard drive was frozen. The drives in all of the Tandy machines are MFM. I needed to source a replacement and obtained a nice working Seagate ST-251 42MB drive from eBay after consulting Frank Durda's Tandy MFM Hard Disk Drive Reference. As you may know, you cannot simply drop in a replacement MFM drive like you may do on a PC. The Tandy controllers used the famous orange-white-yellow wires which were originally connected to various places on the drive logic board. These wires are used to drive the Activity lamp and the write protect feature. Now, this works fine if you are using the original Tandon drives, but those drives are exceedingly rare these days. I found an excellent remedy that was originally documented by Roy T. Beck in TRS-80 HD Bubble Repair document. The Beck method moves the wire attachment points from the drive logic board to the drive controller board. Once this method is applied, almost any MFM drive can now be used with Tandy HD systems.

    IMG_0959.jpg
    The 8x300 Controller with the Beck Modification

    I powered up the unit and the green Active light came on after a few moments. The red Protect switch turned on and off correctly so I apparently applied the Beck mod correctly.

    Now I was ready for testing with my Model 4. I soon discovered that the RSHARD6 driver would not recognize the drive. Great. I assumed the ST-251 was ok for now so I started investigating the 8x300 controller. This controller was originally used in the first 5 MB Tandy drives that were released for the MI/MIII. The controller is essentially unchanged in the 26-4152 12MB unit. There are a few adjustments that can be made on this unit and after careful reading of the 5 Meg service manual and a few articles by @TRS-Ian in past issues of the TRS8BIT newsletter I was able to make the appropriate adjustments to the controller.

    IMG_0961.jpg
    Testing the 26-4152 with a Model 4

    Finally, I was able to create and format a few partitions in LS-DOS 6 on the Model 4 using RHSHARD6 and RSFORM6.

    I now have a working 12 Meg Disk System that I will next be moving to my Model 16 and attempt to build a working TRSDOS-16 environment.
    Last edited by pski; September 16, 2015, 06:52 AM.
    Pete
    http://pski.net

    #2
    Nice work. Its a pity we end up having to buy new MFM drives....
    Dave
    G4UGM

    Looking for Analog Computers, Drum Plotters, and Graphics Terminals.

    Comment


      #3
      5 yr old post, I know, but here I am.... I am going to be replacing the original 5Mb drive with an ST-225. Would you be kind enough to elaborate on what adjustments you made to get RHSHARD to work? You mentioned:

      "Now I was ready for testing with my Model 4. I soon discovered that the RSHARD6 driver would not recognize the drive. Great. I assumed the ST-251 was ok for now so I started investigating the 8x300 controller. This controller was originally used in the first 5 MB Tandy drives that were released for the MI/MIII. The controller is essentially unchanged in the 26-4152 12MB unit. There are a few adjustments that can be made on this unit and after careful reading of the 5 Meg service manual and a few articles by TRS-Ian in past issues of the TRS8BIT newsletter I was able to make the appropriate adjustments to the controller."

      Thanks!

      Comment


        #4
        Originally posted by NoPizzaTonite View Post
        5 yr old post, I know, but here I am.... I am going to be replacing the original 5Mb drive with an ST-225. Would you be kind enough to elaborate on what adjustments you made to get RHSHARD to work?
        Hell if I can remember! LOL!

        Seriously though, I'm pretty sure it was performing the HD alignment procedure.

        Pete
        http://pski.net

        Comment


          #5
          If you are replacing the hard drive in the 5MB enclosure, you will want to review this document for how to reposition the wires that Pete mentioned. Driver modification should not be needed. I did this years ago with a Seagate ST-4038 drive.
          Attached Files

          Comment


            #6
            Thanks lafos - Yep - was following that pdf file - I have the very same controller as Pete - so his wiring picture came in quite handy - just wasn't sure if there were any other mods (outside of maybe alignment Pete alluded to) - going to see about making a youtube video of my upgrade

            Comment


              #7
              Must be the season for it, as I just resurrected a Tandy external 5MB drive with the same controller board. In addition to the the three-wire mod and alignment, I'd suggest reviewing the technical bulletins ("TBs") to verify that all required mods are in place.

              Comment


                #8
                Originally posted by shirsch View Post
                Must be the season for it, as I just resurrected a Tandy external 5MB drive with the same controller board. In addition to the the three-wire mod and alignment, I'd suggest reviewing the technical bulletins ("TBs") to verify that all required mods are in place.
                Good point - I got them here:
                http://www.trs-80.com/wordpress/tandy-radio-shack-memos-bulletins-and-releases/

                There were only a few pertinent bulletins for my 8x300 controller/5MB drive 26-1130/1

                Comment


                  #9
                  Originally posted by NoPizzaTonite View Post

                  Good point - I got them here:
                  http://www.trs-80.com/wordpress/tandy-radio-shack-memos-bulletins-and-releases/

                  There were only a few pertinent bulletins for my 8x300 controller/5MB drive 26-1130/1
                  Yes, but there are (3) critical ones: HD:12, HD:20 and HD:23. The second of those is a real PITA, but necessary.

                  Comment


                    #10
                    Originally posted by shirsch View Post
                    Yes, but there are (3) critical ones: HD:12, HD:20 and HD:23. The second of those is a real PITA, but necessary.
                    I saw HD20/23/25 as the key for me - (I looked at HD12 but don't think it applies for me since I'm not using an 8" system)
                    I know what you mean re:HD20 though. I'm going to forego it for now since I don't recall ever having VCO issues with the current drive.
                    I'm avoiding the complete controller board alignment, of course - but I'll see if this is an issue once I put in the new MFM drive.

                    When you updated your drive, did you actually have the VCO issue, or did you perform this out of an abundance of caution?

                    -Alex

                    Comment


                      #11
                      After spending a lot of quality time on the Tandy repair Discord alongside the original service and technical folks I've learned that they didn't publish these TB docs for the fun of it. Can be a bit tedious to implement some of them, but there was always a good reason to do so. Obviously, YMMV.

                      Comment


                        #12
                        Originally posted by shirsch View Post
                        After spending a lot of quality time on the Tandy repair Discord alongside the original service and technical folks I've learned that they didn't publish these TB docs for the fun of it. Can be a bit tedious to implement some of them, but there was always a good reason to do so. Obviously, YMMV.
                        Totally understand where you're coming from. My thought process is to see how it behaves before doing HD20 - I can't imagine they would have had to perform this for every hard drive they sold in the description. As I mentioned, I didn't *seem* to have VCO issues with the current unit before the original drive decided to lose its bearings, which is why I asked if it was an actual issue for you

                        If I was having issues, then yes - I would turn to the service bulletins to see if there have been a fix. But if my drive was performing,

                        Again - completely understand your logic.

                        Comment


                          #13
                          Originally posted by lafos View Post
                          If you are replacing the hard drive in the 5MB enclosure, you will want to review this document for how to reposition the wires that Pete mentioned. Driver modification should not be needed. I did this years ago with a Seagate ST-4038 drive.
                          SO I made a YouTube video of my MFM conversion using Beck's 3 wire mod. Took less than an hour and worked like a charm.

                          video: https://youtu.be/Z9W2nqhDtzE

                          I used an ST-4038 hard drive as well. Would you happen to remember how you partitioned your drive? I'm on the fence about how to break mine up

                          -Alex

                          Comment


                            #14
                            Disregard my last post lafos - I found your ST-4038 configuration document from 2019

                            https://www.vcfed.org/forum/forum/ge...-meg-hard-disk

                            - it was very helpful!

                            -Alex

                            Comment

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