HP DAT40 (DDS4) drive

• Main page

Drum subunit

This subunit contains the drum with heads and amplifiers, the motor to drive the drum and a transformer for power supply and signal transmission.

Disassembly

First remove the controller board as described on the main page.

Now look at the drum. On the front side (inside the groove) you can see the read head A:

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Read head B viewed from the top:

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Head viewed from the side:

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The black plates on the bottom are the transformer.
The upper plate should be able to rotate together with the drum freely. But on my drive the mechanism was blocked.

On one head I saw some thin red thing:

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First I thought the head is damaged and its the wire from its coil that have blocked the drum.
But it was only dust and not connected to the head. I removed it with the tweezers.

Note the balancing disc on the top (according to Wikipedia, the rotational speed is up to 11400 RPM):

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There is a second one on the other side:

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Remove contact

Note the contact from the metal plate to the shaft:

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Contact removed:

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Disassemble drum motor

First remove the bottom balancing plate:

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Then remove the coil board (the coils are created with copper traces on the board):

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The rotor magnets are inside this ring:

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Remove the drum subunit

Because the drum shaft was still blocked, I removed the drum subunit from the drive:

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Some detail pictures of the drum assembly

Wires of head coil:

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Head position in groove:

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Transformer coils:

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Remove top balancing disk

Remove the top balancing disk:

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Amplifiers of the heads:

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End of the story

I was unable to further disassemble the drum unit with the available tools.
It was still blocked and I decided to give it up.
I applied real force and now I was able to turn it. There was an unhealthy sound, something must have been jammed between the transformer plates.
After some turns the resistance goes away, but the unhealty sound was still present.
After some time it rotates very easily again and I reassembled the drum subunit.
After complete reassembly of the drive, the drum now spins again when I insert a tape.
A real test, if it is still working, was not possible because the Capstan subunit seems to be dead:
The drive takes the cartridge, spins up the drum and pull in the tape. Then it pushes the tape with the rubber roller against the capstan but there is no tape movement.