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.
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.
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.
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.
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.
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.
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.
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.
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.
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