M20 Olivetti M20

Typical problems and solutions concerning the M20 disk drives

A M20 drive unit The Olivetti M20 disk drive unit is a full size 5 and 1/4 inches unit and can be affected by several aging problems. The first good habit to take is to store the machine with the disk drives open, as the heads can stuck together.

The drive TTL electronic board The electronic board of the disk drive is composed by standard components such as TTL integrated circuits, discrete transistors and resistors, capacitors. If you suspect a problem concerning this board, you should begin checking the most sollicited components, such as the transistors controlling the motors, or the capacitors that can be dried out. The power transistor with the radiator controls the disk spin motor and is particularly faulty. If the activity LED is on, but the disk does not spin, check carefully this part.
Andreas Senk reported this experience: "Disk drive 1 had run at full speed the whole time when the M20 was powered up. A transistor named TIP115 was defect. Ive replaced it with the same type and made a speed adjust."

The drive mechanics The mechanics of the drive is one of the most frequent cause of failure. You should chech that the belt is in good shape and that the motor drives correctly the spinning wheel. You can regulate the speed of the disc rotation by using the stroboscope principle and a fluorescent light. Make the center wheel spin and, by observing it under a fluorescent light, the indication that corresponds to the mains frequency in use in your country should stay still. Check also the head positioning system. Under the second motor, there is a spiral which sets the position of the head. Check that everything goes smooth.

The drive mechanicsIf your drive seems to work unreliably, is unable to be used for booting the system, can not read floppy written by other units, it is possible that there is an head misalignment problem. You can try to unscrew a little bit the stepper motor which controls the head position and to rotate it slightly, in order to see if you are able to improve the situation. Be careful, anyway! The head positioning is very sensitive and a slight tolerance can make the drive not working at all. It is better to mark the initial position of the motor, in order to have a reference.

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