EME-150A at 670 rpm

[papichapo]

Hi all,
last summer, after almost 10 years, I've unpacked my old DDI-1 and plugged it to my 464. After having changed the belt, it was all okay 
Last week, I've made the same test but the noise motor was louder than expected.
After some investigations, I've found the motor was running at 670 rpm 
On the PCB, the VR201 cannot reduce this speed (just 1/2 rotation allowed).
Any clue ?

[tjohnson]

normally there is a pot on the motor to adjust the speed.

[papichapo]

No, I as said, on this model, the only way to adjust motor speed is by the way of a PCB pot, not on the motor.
And the tune is limited to 1/2 round, not enough to divide the speed limit by 2...

[Bryce]

If the speed is anything above 350rpm, then it's not the pot that needs to be adjusted. It's usually a dry joint somewhere else on the PCB.

Bryce.

[papichapo]

Does someone known what are current values am I supposed to find on the 4 wires solded to the motor : red, orange, yellow and brown... and of course where to check between...
The plug connecting to the PCB shows me correct values : I've 12 V (red wire) and 5 V (orange one).

[Bryce]

The motor is a stepper motor, there won't be any stable voltage on any of the pins. It gets square waves sent to it from a driver IC.

Bryce.

[tjohnson]

No, I as said, on this model, the only way to adjust motor speed is by the way of a PCB pot, not on the motor.

Actually just to be rather pedantic you didn't say that, you said "On the PCB, the VR201 cannot reduce this speed (just 1/2 rotation allowed)" you didn't mention the motor...

[papichapo]

My apology, but I thought that giving the exact model of the drive in the topic title would have been enough to be understood...

[Vitop69]

If the speed is anything above 350rpm, then it's not the pot that needs to be adjusted. It's usually a dry joint somewhere else on the PCB.

Bryce.

Hey Brice, what do you mean exactly with "dry joint".

[Bryce]

If the speed is anything above 350rpm, then it's not the pot that needs to be adjusted. It's usually a dry joint somewhere else on the PCB.

Bryce.

Hey Brice, what do you mean exactly with "dry joint".

A dry joint is when a solder joint cracks, either due to bad soldering, or in the case of retro computers, because it's extremely old and had some sort of dynamic movement being applied to it for years. They usually look like this (below), but might not always be so obvious.

Bryce.