Technics SL-1400 speed problem

turning japanese
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Tom_Technics
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Technics SL-1400 speed problem

Post by Tom_Technics » 04 Jun 2019 22:07

I have a Technics SL-1400 with a strange speed problem. At both 33 and 45, the platter struggles to start spinning and rocks backwards and forwards and then spins with a consistent juddering or pulsing motion if it's given a slight push in the right direction.
A previous owner had previously replaced the electrolytic capacitors with poor quality generic parts, most of which had very high ESR. I replaced them all with quality Nichicon ones, replaced all of the solder on the motor board, cleaned the speed selector switch via disassembly and also the pitch control potentiometers. The behaviour remains unchanged.
Given it's behaviour, it would make sense that the issue is with a transistor or diode. I'll have to wait a few days before I can get back to this project so I thought I would post the details of the issue here to see if anybody has experienced the same behaviour with a similar unit, so practically any non-quartz IC controlled Direct Drive turntable.
I really hope it isn't the chip. I have a spare from an SL-D3 and another from an SL-1600. Both of those units use variants of the AN630 but I'll have to dig deeper to work out if they're compatible. Anybody know if they are? Out of curiosity, has anybody come across a non-quartz Technics Direct Drive with a failed chip?

sylvain999
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Re: Technics SL-1400 speed problem

Post by sylvain999 » 03 Jul 2019 00:43

Did you check the DC voltages ? Did you check or by- pass the power switch? ( looks strange that i ask for this but they are notorious for oxidizing and not letting anough current go through) If all looks good chances are the chip has gone .One way you could try isolating the problem is to heat it with a drier or heat gun or freeze it with freeze mist and see if that changes the behavior of the platter.

gazzatron
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Re: Technics SL-1400 speed problem

Post by gazzatron » 08 Jul 2019 12:22

As a first step, I would replace the main filter cap 470uf/50v which has been known to fail and eventually damage the motor and/or the IC AN630. But you said you've replaced all caps; have you included the cap I've suggested ? Also , I hope the NP (non polar) caps have been replaced with new non polar caps.

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