Task: Diagnose and Fix an Atari 1050 Disk Drive
Needed: 1050 Disk Drive
Time: 30-60 mins
Introduction
Everyone hates that dreaded moment when an Atari disk drive won’t boot. Fortunately, there are a number of common issues which are relatively easy to address. I finally got around to diagnosing and fixing three 1050 disk drives I have had sitting in storage for many years. This was my first attempt to do this, and I found it a bit easier than I had imagined. Below are the steps I went through in getting these drives running. This is not an exhaustive list, but will likely fix 90% of the problems.
Instructions
The first thing to try for a drive failing to read a disk is to clean the drive head. I have described how to do this previously, and it only takes a few minutes. The other common thing to do is to grease the rails shown below as the steal rods in the center of the photo. A very small amount of white lithium grease is recommended. I have never had to do this.
The second step is to download and boot the Atari Consumer Products Service (CPS) 1050 Diagnostic Diskette ATR file. This is available from the Internet Archive. Boot this via SIO2PC, FujiNet, or similar device on you Atari 8-bit computer. You can also make a real disk using the Atarimax ProSystem software which is what I did. Make sure your 1050 disk drive is connected to you Atari computer with a formatted disk in the drive. Choose the first option (#1) from the CPS software menu. This will start the diagnostic process. Each of the items tested is described in the field manual (see page 31). All three of my drives failed the motor start, motor speed, head step and settle, and track 00 tests. Failure of the controller or invalid command tests means you likely have one or more bad chips.
Assuming you failed one of more of these tests you will need to crack open the 1050 for the repairs below. Remove the four screws on the bottom of the unit as well as the two screws holding the black faceplate to the unit. The top comes off easily by moving it toward the front of the unit. The drive mechanism lifts off easily for the belt check mentioned below.
One of my drives was not even spinning the floppy disk in the drive. I discovered that the belt underneath the drive mechanism had come loose. The loose drive belt was easy to slide back on and solved the problem.
The remaining two drives required adjusting the drive speed and the track zero sensor to get working.
To adjust the speed first run option #2 (troubleshooting) from the main menu of the CPS software and then choose the drive speed option (#1). The drive should start spinning with speed estimates provided by the software. If it is below or above 208.3 you will need to adjust the very small screw on top of the blue box shown below. Note that these usually have a plastic material on them to prevent movement. You will need to gently chip away at that reveling the head of the screw. This can be turned using a really small flathead screwdriver. Turn it slowly to the left and right while watching the speed on the screen. The unit is on so be careful not to touch anything else or you might get a shock.
To adjust the track zero sensor simply loosen the two screws shown below just above and below the sensor. This allows it to be moved toward the front or rear of the unit. The CPS software has a troubleshooting option for the sensor so you can monitor it in real time.
Once you have made your fixes be sure and run the CPS diagnostic software again to make sure it works before putting it all back together again.
There are other suggestions in the field service manual. I did not need to explore any others and thus won’t cover them here.
Comments
I am really happy I now know how to adjust the drive speed and adjust the track zero sensor. This combined with cleaning the head and greasing the rails will likely get you a working 1050. If not, there might be more serious problems like defective chips or a bad drive motor. I am very happy to get these three drives working again without too much pain and suffering!
Note that the CPS diagnostic software will not work with a drive that has been modified with a Happy or Speedy board. It will fail the same tests associated with the speed being off.
There are a number of threads on the AtariAge about 1050 drive repair. These are worth browsing if you are still having trouble with your repairs.