Hitachi SDT-170 Music Centre / Record deck problem, motor too slow.

[musicman334578]

Hi all

I have aquired the above Music Centre left from a recent bereavement in the family.

The record deck has had a correct new replacement belt, all spindles cleaned and grease free. Lubricated main turntable spindle and motor below the belt drive spindle on the motor.

It is running a little slow and the motor needs to be adjusted to slightly increase its speed. However, I just cannot seem to find the small adjustment screw which allows you to do this. Any ideas where it might be located?

Thank you all very much.

Best wishes

[ben]

In cases like these, you need to determine if this is a DC motor (which will likely have a pot nearby) or an AC type (which will not). If the latter , then usually a strip down-clean-relube of the motor bearings helps.

[nickdoofah]

I believe this model has a synchronous AC motor which cannot be adjusted! Some turntables were like this at the time - Somewhat frustrating to say the least!

[musicman334578]

Thank you both very much

[_Clint_]

Depends how slow it is but you can get some adjustment by wrapping cotton around the larger pulley effectively increasing the size, or if you dare sanding with a V shaped emery cloth the motor pulley decreasing its size.

You can also get a tiny amount of adjustment by unscrewing the motor and pushing it away from the other pulley and tightening back up.

The mains frequency nowadays is pretty rock steady so it should be a once in a lifetime adjustment.

[roffe]

I have the SDT170 service manual.Unfortunately nothing is said about how to adjust speeds.
However,a look at the motor control circuit should be enough.

[SiriusHardware]

For the benefit of the OP, who inherited this unit and may not be a fluent circuit diagram reader, it looks like RV851 and RV852 are the speed setting controls.

RV851 sets the speed when the speed control switch S851 is open, and is the only control which affects the speed when S851 is in that position - so this adjustment MUST be set first.

When that speed is set correctly, close S851 (Change to the other speed) and adjust RV852 until the other speed is correct.

Be aware that RV851 affects BOTH speeds, whereas RV852 affects only one speed, which is why they have to be adjusted in the order described.

If the deck is running slow on both RPM speeds, then adjustment of RV851 (only) to correct the speed on one RPM setting may also correct the speed error on the other RPM setting. More likely you will need to set one speed, then the other as described above.

[crackle]

Originally Posted by _Clint_

Depends how slow it is but you can get some adjustment by wrapping cotton around the larger pulley effectively increasing the size, or if you dare sanding with a V shaped emery cloth the motor pulley decreasing its size.

You can also get a tiny amount of adjustment by unscrewing the motor and pushing it away from the other pulley and tightening back up.

The mains frequency nowadays is pretty rock steady so it should be a once in a lifetime adjustment.

Sorry Clint I think you are mistaken.
I thought the OP said things were running slow and he wanted to speed the playing up. Reducing the effective size of the motor pulley or increasing the size of the driven pulley will make matters worse and it will play slower.

Mike