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Sony DAT DTC-790 "Caution"

Insert tape, then power on...sound of motor spinning about 6 seconds, at the 4 second mark the little white gear indicated by the arrow moves back and forth (about 1/8"), then stops. After 6 seconds motor sound stops and is gone, then tape is brought into machine. Head drum never spins, and is always free.
 

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The white gear is driven by the loading motor through a belt, so the belt is probably ok.

The white gear directly drives the arms through gears with just 2 small springs to avoid jerking.

I am not sure to understand how much it rotates (you mean 1/8 turn ?). But does the large dark green metal gear on the right of your picture also rotate, at least a little bit ?

Best would be to make a video.
 
hdrobien said:
The white gear is driven by the loading motor through a belt, so the belt is probably ok.

The white gear directly drives the arms through gears with just 2 small springs to avoid jerking.

I am not sure to understand how much it rotates (you mean 1/8 turn ?). But does the large dark green metal gear on the right of your picture also rotate, at least a little bit ?

Best would be to make a video.
Click to expand...
The little white gear doesn't rotate at all. It moves 1/100th of a turn to the left then bounces back as if something is stopping it.
Will be back to the machine Wednesday. Thanks again.
I'm guessing I will have to remove the assembly to see what's underneath.
 
It is very likely that the mechanism is blocked by the old grease, which is relatively usual for this model.

Repair requires a fairly extensive disassembly, and is not easy.
 
SaSi said:
If you have removed the transport mechanism (4 screws to the bottom of the chasis), then you should have access to a white horizontal gear slightly protruding at the right edge in the front. Try to rotate it in both directions. It should move the tape loading arms towards the drum and away from it depending on which way you rotate it.
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On my deck it was a black gear, both arms moved well enough, although the mechanism on it's own had a real hard time getting them up where they belonged, inevitably the deck fell into "Caution"
I hate to say it and I feel like a real grease monkey, but all I wound up doing was shooting a few drops of WD-40 into the top of the motor and surrounding gears.
It's been a couple hours now and the deck seems wonderfully happy!
This will make only the 5th DAT I've managed to repair in 55 years, although obviously they weren't around that long, and here in Connecticut very very few were sold.
Click to expand...
 
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