Help with a hotpoint w/m motor

[Brian]

I've got a hotpoint washer / dryer that isn't rotating the motor. So I'm hoping to find a hotpoint or motor expert who can help me..

So heres an interesting puzzle for you :) -

The motor says on it AC motor for electronic speed control,

1 phase. (904/1153/10). This is UK 240v.

When it stopped working I took the motor out and replaced the brushes, but its still dead (the rest of the machine functions).

There are 7 pins going into the motor, with a 7 block connector going in.

The wires going in are labeled 1-7 going left to right, and all are white except pin 1 = sort of purple / lilac, and pin 5 - red blue stripes.

I've stuck a multimeter on the motor, and can see that pin 2 goes into one brush, pin 3 into the other. When connected, there is about 7 ohms across the armature (which indicates the brushes are probably contacting ok), i.e. across pins 2-3.

Pins 1, 4- and 5 seem connected (~1 ohms) .. I find it odd all 3 are connected, but I don't know if thats normal.

Across pins 6-7 is 1.6k ohms. A close look reveals two thin wires from these to the end of the motor, so I'm guessing this is the tachometer?

The above measurement were all with the power off.

I put the mulitmeter into AC volt mode, stuck one pin on earth (chassis), and sticking the machine into slow 'tumble' mode checked the voltages to the unconnected pins, which follow.

I'll put this into a little table to see if that helps: The table was done in notepad in courier new if the formatting is a mess in your reader.

1 2 3 4 5 6 7 Purple White White White Red/Blue White White

->6,7 Armature Armature ->1,5 ->1,4 ->7(1k6)

[Andrew Gabriel]

The format works fine.

If there's really 235V across the armature and the motor isn't turning, then there will be clouds of smoke within a few seconds. This implies there is a break somewhere in the armature circuit. One possibility is that there is a one broken armature winding and the motor happens to have stopped with the brushes on that one. Maybe the brushes are not making proper contact with the commutator?

After you've had power on the motor (and isolated it again), are any of the windings warm (be careful as they could be very hot)? I presume you can spin the motor by hand with the power off, i.e. it hasn't got a ceased bearing?

Not possible to tell directly from your measurements, but it looks to me like there could well be no voltage across the tachometer as both sides measured the same voltage.

1, 4 and 5 are presumably the field windings. It looks like 1 and 5 or 4 and 5 have a supply on them, and the other connection is probably for operating the motor at a completely different power/speed, such as the final spin.

BTW, don't try operating the motor with no load. In theory, the microprocessor should limit the speed using the tacho, but in mine the microprocessor crashes if you run the motor with no load, and hence fails to limit the speed or stop the motor (have to power off the machine). Washing machine motors when run with no load and no speed control can way over-rev, and cause the armature to explode into pieces.

I have had brush failure on a motor also blow the SCR (semi conductor power switch) on the control board, but the evidence you have presented so far doesn't point to this having happened.

[Brian]

Thanks for the reply. Perhaps I wasn't clear in the original post but I did the above voltage readings straight out of the connector that goes into the motor, WITHOUT the motor attached. Maybe this was .. stupid, but its not easy to access them otherwise, and I was running out of ideas. I wanted to see what was being sent, unloaded. I suppose it may ramp up the voltage in order to power the ghost motor. But it did show it wants to stick power out.

Prior to this I got about 7-8 ohms across the armature pins of the unconnected motor so I assumed the brushes touched ok, and that was the total impedance across the windings.

Its definitely not ceased. I'll see if I can check for warmth later.

Ahh I see your point, if both are in phase. Hmm. Don't know whats supposed to be across it. I kind of imagined it would be a signal out that is induced, with nothing passed INTO it.

Ok.

Yes thanks, I read that on the net. I'm surprised there isn't a 'here is how hotpoint wire their motors' article, but I just can't find one anywhere.

One final note - the controller block is definitely a lot noisier than it used to be. But everything else (pumps / heat etc) all work. Its just the motor won't turn.

I was trying to get the controller out to have a look at the solder joints on the bottom but can't seem to get at a couple screws. Maybe thats for tommorow!

[Brian]

Thanks for answering,

Yes, I can see it. I've found the replacement part for this module on the web. 25 quid I think it was.

Ahh ok. So an oscilloscope would be handy!

Hmmm I've now got the controller and module out... AHA! It wasn't obvious, as the module had a load of visible components, then some under a heatsink. Now that I have it in my hands with a torch: I can see two resistors that look blackened towards the bottom corner. And what looks like a transistor that is missing its face, right next to another blackened resistor. Its not a power tranistor, its a .. normal looking one next to one simlar marked C556. All these were under the heatsink so I didn't notice until I took it apart.

So thats handy, I know that this needs replaced. I don't know what the actual components were though, so in the abscence of a circuit diagram or a workaround, thats a new module. One other query is, there is a large relay I believe marked EKS EMK025 on the back of the controler, with pin that comes out attached to a plastic lever. It doesnt seem to move at all when its. Maybe thats for spin mode only..

So the FINAL question is, is the motor still ok? Did it blow and take the board with it?

Ok I'm game to wire it up and give it a very quick pulse of 240v. I may do this in situ, in the machine, so its 'loaded'.

But I don't know what precisely to wire it to. Ignoring the tachometer, thats pins 1, 4,5 all connected, and

2-3 over the armature. If you recall. 1 2 3 4 5 6 7 Purple White White White Red/Blue White White

->6,7 Armature Armature ->1,5 ->1,4 ->7(1k6)

[Andrew Gabriel]

Probably a BC556, a common general purpose transistor.

Two likely uses for a relay are to switch the heater element on (high power SPST), and motor reversing (medium power DPDT).

Spin selection on the Hotpoint controller I have is done with a second SCR on a large heatsink.

POssibly caused by bad brush contacts. That happened to me, but I just replaced the SCR's on the board and it was OK again. Yours sounds more significantly damaged.

Still rather risky. The machine controller will never give it a full power burst directly from a stationary rotor start. It may never give it a full mains blast ever, even at max spin.

If I was going to try it, I would connect the field windings and armature in series. You will need a low resistance reading meter to properly buzz out the 3 field winding terminals (or look to see how they're connected, and ignore the tap one). However, you run a real risk of destroying the motor by doing this, and possibly destroying bits of yourself too, without knowing much more about the motor ratings/specification.

When trying to work out what was wrong with mine, I kicked off a fast spin cycle. It was only managing to turn the drum at about 1 rev/second, but that seemed to be enough for the microprocessor to decide the motor was working, at which point it engaged the top speed spin winding. The machine damn near took off as it shot from almost stationary to 1400RPM in about a second, which of course it would never normally do. Those motors are very powerful -- ISTR mine is rated 1.2kW although it probably delivered a lot more in that second.

[BigWallop]

You found the connections that go across the armature through the brushes, so these are the only connections you need to make, to have the motor give a spin. The test we do is with a modified connector, but it only has these two connections made to the motor. The motor is actually single phase, so the other connections are only to give signals to the controller unit from the tachometer coil.

The tacho' coil is center tapped, so makes up two individual coils. One wound one way around the holder. The second wound in the opposite direction. When the magnet spins either way, it still produces the same small signal to the controller. When the machine timer selects a full spin state the two coils become one and as the magnet spins, the controller has the full coil to check on to make sure the motor is up to full speed.

So you only need to make the connections to the motor on the two points that pass through the brushes and the commutator on the armature. Remember to hold the motor down with your foot, or another large heavy object, before you plug in and switch on.

Hope this helps a bit more.