Numark TT1650 Slows Down Fault

The TT1650 is a turntable manufactured by the Numark Company. They are one of the largest and finest manufacturers of DJ equipment.

I bought this faulty turntable and managed to repair it. The turntable slows down and then stops. Sometimes it plays for a while and then begins to slow down finally grinding to a complete halt. The fault can vary a little. For example, there are some days when the turntable plays fine for many hours without any problems, however some days it plays only for a minute or two, then starts slowing down, and then grinds to a complete halt. Sometimes, the speed oscillates as if it was stuttering.

At first, I thought that it might be the motor, however this is a brushless motor, and they usually never wear out. They tend to be very reliable with an excellent record of accomplishment. Nevertheless, being an electronics engineer I decided to open it up to have a look.

The first thing I noticed was how hot the motor driver chip was getting. It was so hot that you could not touch it without burning your fingers. There did not appear to be any short circuits anywhere and neither did it appear to be drawing abnormally high currents. The documentation sheet for this chip indicates a normal operating temperature of up to 75 °C.

Loose Heatsink

One obvious thing I noticed was that the heatsink had become loose probably through periodic expansion and contraction of the metal bolts, or perhaps mishandling. I decided to remove it completely, and clean away the dried thermal compound, with the purpose of re-seating it properly with new compound. Once the chip was firmly bolted back on I decided to re-solder the pins where the solder was showing signs of cracking and drying.

This seems to have solved the problem and I managed to get away without having to replace the motor driver chip.

With the new range of DJ turntables coming out these days it is probably not worth fixing this old turntable unless you happen to be an electronic engineer, have spare time, and can get the replacement chip easily and cheaply.

With inflation, many of the suppliers have dropped their prices and you can pick-up some fantastic DJ gear for almost nothing these days.

As you can see, they glue the bolts in place to stop them from creeping, however due to the heat the glue dries up and no longer secures the bolts. This results in the heatsink getting loose. A poor thermal contact results in the chip overheating.

I managed to repair it without having to replace the whole chip however, I am sure that there might be others where the chip is so badly damaged that it would need replacing.

Please note that this article is for a qualified electronics engineers. Do not attempt to repair your turntable if you are not an experienced qualified electronic engineer.

In the following sections of this article, you can see the dried solder on the other side and how I repaired it by simply re-soldering it.

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