Marantz TT-4000 / SM6415A-4S motor controller
Hi all,
I'm trying to repair a Marantz TT-4000 direct-drive turntable that turns much too slowly and quite irregularly. I found its service manual via Vinyl Engine - The Home of the Turntable and by comparing the waveforms on the pins of its SM6415A-4S motor controller IC with what is drawn on the schematic, I can see that some waveforms are spot on while others are way off.
Unfortunately I haven't been able to find a datasheet for the SM6415A-4S and on the Marantz schematic it is just a rectangular box with 22 pins. Does anyone have a datasheet or a block diagram with pin numbers? Or experience with failing direct-drive turntables?
Best regards,
MarcelvdG
Hi all,
I'm trying to repair a Marantz TT-4000 direct-drive turntable that turns much too slowly and quite irregularly. I found its service manual via Vinyl Engine - The Home of the Turntable and by comparing the waveforms on the pins of its SM6415A-4S motor controller IC with what is drawn on the schematic, I can see that some waveforms are spot on while others are way off.
Unfortunately I haven't been able to find a datasheet for the SM6415A-4S and on the Marantz schematic it is just a rectangular box with 22 pins. Does anyone have a datasheet or a block diagram with pin numbers? Or experience with failing direct-drive turntables?
Best regards,
MarcelvdG
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It looks like I made a very silly mistake, the silliest I've made in years.
A couple of weeks ago, I had the impression that the turntable turned slower than usual, but I didn't check it by putting on a record. So I put it upside down, removed screws and started measuring. The measurements showed that the PLL was oscillating and didn't lock.
So I did some experiments, such as measuring open loop. Open loop, everything appeared to work normally. I also replaced an electrolytic capacitor in the loop filter, just to be sure.
Only today I realized that when you remove the platter to turn the turntable upside down, you remove its moment of inertia, which changes the loop dynamics. The PLL is only unstable when the platter is removed, it locks normally with the platter on.
So all in all, it looks like I've literally been trying to fix something that ain't broke.
A couple of weeks ago, I had the impression that the turntable turned slower than usual, but I didn't check it by putting on a record. So I put it upside down, removed screws and started measuring. The measurements showed that the PLL was oscillating and didn't lock.
So I did some experiments, such as measuring open loop. Open loop, everything appeared to work normally. I also replaced an electrolytic capacitor in the loop filter, just to be sure.
Only today I realized that when you remove the platter to turn the turntable upside down, you remove its moment of inertia, which changes the loop dynamics. The PLL is only unstable when the platter is removed, it locks normally with the platter on.
So all in all, it looks like I've literally been trying to fix something that ain't broke.
Last edited:
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