NSM City II carriage does not move to the left

[jukenorman]

Yes I was thinking you should start by looking at the square waves going to IC500. From the description in the document, I think it should now be possible to successfully fault find the electronics.

Norman.

[jonassandstedt]

Hi Norman,
I have now tried to measure, but I cannot reach the PCB sufficiently when plugged into the jukebox.
I measured between TP and ground, the wave looked as the picture in the schematics. I then measured between ground and the ANM motor plus terminal, and the signal looks quite differently for the different drive directions. I cannot add pictures here, but in the “faulty” direction the voltage occurred in bursts. If you give me guidance, I can perform more measurement.
Best regards
Jonas

[jukenorman]

Hi Jonas,
It's a DC motor so you should be seeing DC voltage. Maybe you should try measuring this DC voltage in the good direction noting which is the positive and negative poles. In the other direction, theses poles should reverse (obviously!) but you may be able to gather information from doing this - maybe only one pole is switching for example?. It's transistor switching so one set of transistors has to turn off and another set turn on to enable the motor to reverse.

Norman.

[jonassandstedt]

Thanks Norman,
Probably I should know the answer to this question, but ask anyway.
I assume that I should measure between the + pole of the motor and ground, and between the – pole and ground for both directions, should at least one pole be disconnected from the DC motor then?
Best regards
Jonas

[jukenorman]

Hi Jonas,
Measure between + and -ve on the motor, first going in the good direction, then measure the + and -ve to ground. Then do the same for the opposite direction. I'm fairly sure that the -ve should be ground (I would need to look at the schematic) but since the -ve is also switched, doing the checks that way could provide more information on the problem.

Norman.

[jonassandstedt]

Thanks Norman,
I will try that.
According to the schematics, the motor terminals are connected to a respective junction between transistors T515/T517 and T514/T516, and separated by motor capacitor C505. The negative motor terminal is not by default connected to ground, but the motor terminals are grounded when the respective transistor T516 and T517 is opened.
Best regards
Jonas

[jonassandstedt]

Hello Norman,
At last there has been success, although I have to admit I would never have been able to figure it out “the hard way”. Wednesday evening this week I measured with my USB oscilloscope, and it took some time because I had trouble initializing the oscilloscope. When it finally worked, I measured, and it looked bad when the DC motor ran in the “wrong” direction - when all of a sudden it worked and the oscilloscope showed nice DC voltages that changed when the DC motor changed direction. Everything seemed OK and I did not know why; It was late and I went to bed. Next day the error had returned but after a while the DC motor was OK again. Aha, it is a heat sensitive error! I brought my coolant spray and sprayed T510, T512 and when I sprayed T511 the DC motor started to malfunction again. I promptly changed T511, I had a spare at home. But it did not help, and then I noticed C507 that also get some coolant spray when I spray T511. I gently squeezed C507 and the spin of the DC motor changed accordingly. Today I found a 1uF 50V (should be 63V) capacitor and replaced the suspected C507 – and now it works. I must admit that I would not have been able to logically deduce this from oscilloscope measurements, well, not for a long time anyway.
Best regards Jonas

[jukenorman]

Hi Jonas,
Really glad you got it fixed! It was worth persevering with - sometimes we deserve a lucky break!

Norman.

[jonassandstedt]

Hello Norman,
I would like to thank you for the encouragement and technical material that has helped me to continue and not give up. And thanks Hildegard for supplying the rare service notes and relevant schematics.
Best regards
Jonas

[Hildegard]

Hi Jonas,
How nice you got the City II back to working! Good job which includes to follow Normans hints and suggestions. I couldn't have done so.

Great - now you can enjoy listening to the City II. And instead of Norman and me - invite two friends for a beer. 

Hildegard

[jonassandstedt]

Yes, indeed I will.
Now I can relax from the City II and tend to other projects that hopefully are no that going to take that long time.
And next time the City II malfunctions I will know a little more about how it works than when starting this project.
Best regards
Jonas