Gx400d-ss

Akai Junky

New member
I am new here so thanks for letting me in . Hope to learn a thing or two. Just got a great deal on a couple decks . One is a GX400d-ss with all metal front (not black )and the other a Gx630d-ss off an older musician who was downsizing . After much cleaning and degreasing ,and tweeking I had both of them working great .

However after I got the Gx400d-ss back together the servo motor(scm3-16tw) that drives the capstans stopped working . I have isolated electrically the motor to determine if it is the motor itself(still spins smooth and clean )it does:). I am not getting any AC voltage at the motor , should be roughly 70 vac and below .

Upon closer inspection of the servo board I found 48 volts dc across a relay on the board where there should only be 24 V . Perhaps this relay is burned out due to a regulation transistor going ??

Rewind was slow on this unit and after investigation online that is common with this machine . There was a lot of oxidation on the electronic parts . Transistor leads ,pots . Capacitors look good . I do not see any swelling though I am sure I am sure a recap would lift its spirits . Perhaps something on the servo board went or perhaps the power supply ? Those would be my first culprits . Maybe there was one thing that always went on these units and somebody knows :D:D

Everything else on the machine seems to be working . When I pull tape over the heads the amp and machine respond as it should . Rewind and fast forward also work . And before anyone asks the capstan belt is in great shape no sign of wear and tear or age at all . Big belt the one on my power planer is smaller !!


I am new to reel to reels and went from having zero to 4 within 2 weeks . I have caught the bug . I have some experience with electronics . But I know there are guys out there who worked in the service industry for there whole careers back in the day on here who could perhaps help out .

I do know that this is a rare unit (they both are ) this one is a 2 digit serial #. Some estimates are as low as 300 for production . But I would imagine higher . It is built like a brick you know what . I have 1940 military receivers that weigh less !!

I have to get this going again because it sounds so good . I do have a pdf of the service manual ,though it is not the most comprehensive one I have seen. As well the circuit for the servo board is different to what is in the machine .

At least for now the Gx630d-ss will entertain me . Look forward to any help or advice that I get . Thanks
 
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