oscillating spindle sander help?

[mark smith 20Participant @marksmith20]

[mark smith 20Participant @marksmith20]

HI, I was busy using the sander today and then switched it off . When i went to switch back on ,no power. From experience its usually the crappy nvr magnetic on/off switch these things are usually fitted with.

So tried another but remembered it was broke.

Decided to use one out of a cheap grinder but still will not work,the switch rumbles when pressed but will not start.

Any suggestions as i get sick of replacing these cheap chinese switches .Or is something else wrong. Brushes look fine. They are the KJD  switches or similar the one in the machine was unmarked (just 250V 6 amp)

Thanks

Edited By mark smith 20 on 27/05/2020 14:49:38

[Andrew TinsleyParticipant @andrewtinsley63637]

Hello Mark,

If it does turn out to be the switches again, then maybe you should upgrade the switches to better quality ones. I am not being flippant, I have had exactly the same problem with those very same switches. After two failures, in relatively quick succession. I went out and got some good quality items and have never had a problem since.

Andrew.

[mark smith 20Participant @marksmith20]

Could you point to suitable one of better quality as all i see is variations of the same chinese switches on google.

[mark smith 20Participant @marksmith20]

Are these suitable

**LINK**

[Andrew TinsleyParticipant @andrewtinsley63637]

Hello Mark,

The Eichoff switches which you have found would be an excellent replacement. I can't remember what the make of my switches were. I got them from my local factors, I suspect they may have been MEM, I sold on the kit that used them so I cannot check.

I went through the usual Ebay lists and Amazon too and basically found about 3 or 4 versions being sold by hundreds of people. That is when I gave up and went to my local electrical factors.

Andrew.

[mark smith 20Participant @marksmith20]

Thanks , but still puzzled why the working one from the bench grinder doesnt work on the sander . (It definitely works on the grinder as i just checked again.)

The only thing between the motor and switch is this board, which i havent a clue about.

Edited By mark smith 20 on 27/05/2020 15:49:39

[mark smith 20Participant @marksmith20]

No more thoughts, im doubtful that the switch is the problem. The board above is supposedly some crude ac/dc converter .Motor is dc brush motor rated at 450 watts.

Anyone?

[Anthony KnightsParticipant @anthonyknights16741]

The PCB looks like a 4 diode rectifier with suppressor chokes / capacitors and a couple of VDR's.

[Frances IoMParticipant @francesiom58905]

is it possible that the VDR means that the initial current taken by the sander is insufficient to keep the NV switch held – presumably the VDRs are there to limit surge on switch on

Edited By Frances IoM on 28/05/2020 07:50:17

[Joseph Noci 1Participant @josephnoci1]

Posted by Anthony Knights on 28/05/2020 07:35:21:

The PCB looks like a 4 diode rectifier with suppressor chokes / capacitors and a couple of VDR's.

Anthony has it – that board is just a suppressor board -common mode/series inductor chokes and bypass capacitors. The AC is rectified and that seems to be what feeds the motor – Maybe a diode is duff?

Check the diodes, check there is no bad solder joint/wire connection on the underside of that board, and then, if all OK, bypass the magnetic switch momentarily and see if the motor runs- If the Grinder switch works on the grinder and not the sander, I doubt it's the switch – more likely there is insufficient current flow to keep the switch active, which means either faulty diode(s), bad connection somewhere, open winding on armature/stator, bad brushes/connections..

Joe

Edit – one other thing – those blue blobs – sometimes those are capacitors, but sometimes there is a device in series with the supply line that is used for short circuit protection – said device often looks like a capacitor – these devices are basically a resettable fuse –  when cold ( room temp) they are close to zero ohms resistance,but if there is a short, the high current heats it up and the resistance climbs rapidly to megohms, effectively opening the circuit. When cold, all is well again..unless the device has popped open-circuit.

Do you have an ohm-meter/multi-tester? Try to determine from the PCB layout if the one device, the smaller one, lower left in your picture, is in series with the power lines and if so measure across it to see if it is opencircuit. If all those blue devices are ACROSS the power lines, they are capacitors, to be ignored for now..

 

 

Edited By Joseph Noci 1 on 28/05/2020 08:05:53

[mark smith 20Participant @marksmith20]

Thanks for the replies. Im terrible at electrical diagnosis. I do have a multimeter but unsure where to put the probes and on which settings. Heres a photo of some of the components. The only thing that maybe looks odd to me is behind each of those two round things with a coil going round the circumference . Messy black areas on the back of the pcb.

[mark smith 20Participant @marksmith20]

If it helps all the diodes have tested 0.495v forward and OL in reverse.

The two rectangular black capacitors measure 0.31uF (stated on capacitor as 0.22uF),

I cant seem to get any straight stable readings on the blue ceramic disc capacitors (taken from the pins at the back of the pcb.) multimeter seems stuck on nF

 

Edited By mark smith 20 on 28/05/2020 12:09:48

Edited By mark smith 20 on 28/05/2020 12:12:30

[Joseph Noci 1Participant @josephnoci1]

Mark, lets first be sure those blue jobs are capacitors – can you read the text on them at all? It should be fairly obvious if they are caps. Also, there appears to be some legend printed on the board, seems partially under the components? What is the legend under those blue jobs?

The diodes as you measured seem fine.

The larger black inductor – the one tied to the PCB with a white tie wrap – measure with your ohm-meter from the lower left black wire to the upper left black wire in as seen in your image below – then measure from the lower right to upper right – each measurement should show low resistance – if not, try lower left to upper right, etc.

If all low res, that common mode inductor is ok and not open circuit.

Lets take it from there..

Joe

EDIT – not clear in the photo, but it appears that there are 3 black wires from the PCB to the motor – where do they connect on the motor – I would expect 2 ? Is one a ground connection?

Edited By mark smith 20 on 27/05/2020 15:49:39

 

 

Edited By Joseph Noci 1 on 28/05/2020 12:29:55

[mark smith 20Participant @marksmith20]

The blue things are marked

JD222MY1 400v- X1 400v -Y1

The black wire in the middle of the photo going to the right is the earth (screwed to motor casing)

Tested larger inductor.

lower left to upper left 0.4 ohms, lower right to upper right 0.4 ohms (lower left to upper right etc reads OL)

Upper the blue caps it says C4 and C3.

The blue caps measure 4.52nF from the back on the solder joints but dont know if accurate as some solder joints touch others.Cant get to the caps legs from the front.

Edited By mark smith 20 on 28/05/2020 12:32:46

Edited By mark smith 20 on 28/05/2020 12:36:47

Edited By mark smith 20 on 28/05/2020 12:39:22

Edited By mark smith 20 on 28/05/2020 12:46:07

Edited By mark smith 20 on 28/05/2020 12:50:40

Edited By mark smith 20 on 28/05/2020 13:02:18

[Joseph Noci 1Participant @josephnoci1]

Ok Mark. Just to be clear – all THREE blue jobs are marked JD222MY1 400v- X1 400v -Y1 – correct?

ie, they are identical?

If so , they are all three capacitors and will not be part of your problem. They are 2.2nf 400V class X1/Y1.

The only two components left are the two toroids – upper and lower right – Measure across each coils wire ends for low resistance.

Then, instead of measuring all wires/cables for continuity, can you apply mains power safely, bypassing the magnetic switch? The wires end in spade terminals – This trick works – BUT BE CAREFUL – THIS IS NOT RECOMMENDED PRACTICE – PLEASE BE CAREFUL…

DISCONNECT THE UNIT FROM THE MAINS SOCKET _ PULL OUT THE PLUG ETC…!!!

Take two paper clips (!) and press the ends into each of the spade terminals of your cable, ie, in place of the switch. So, using a paper clip as a shorting jumper, connect the PCB end of the cable to the end of the mains cables, in place of the switch. Do this for LIVE and NEUTRAL. Check that the connection is good and firm.

TAPE EACH KLUDGED JOINT UP INDIVIDUALLY WITH GOOD INSULATION TAPE. Make sure there can be NO accidental contact with this thing!

Mains wall plug switch in OFF position, plug in the sander's plug. Make sure the sander motor is stable, the PCB is fixed and nothing can short out because of the kick on startup…

BEING CAREFULL….Switch on..

Did the motor turn or not???

If not..

Switch off and remove wall plug.

You now need to measure some voltages at the motor brushes and on the PCB, so make sure the motor is stable so that you can use one probe per hand and probe about without the pcb moving away etc. You are dealing with a killer voltage here, so CARE IS NEEDED.

Please also make sure your multimeter is safe, eg, probes are in good condition, with no chance of conduction along the probe insulation ( dirty, etc..)

When sure, plug in again, and switch on.

Please be aware that while probing, if there is a loose connection that makes while probing, the motor may start up, startling you. Flayling about with metal probes at that point requires care..

Measure on AC and DC settings, at the motor brush wire connections ( set meter to read 220VAC/220VDC)

If nothing appreciable, then measure at the leads of the two toroids – the toroids are each in one leg of the rectified mains to the motor it seems – so on the lower right one, on the black wire just below the phillips head screw, and on the uppr right toroid, the black wire just above the phillips head screw.

This should be full wave rectified DC, so meter to DC, but try AC as well ( also 220V settings – or greater depending on meter available settings)

Next…

Joe

[mark smith 20Participant @marksmith20]

Bypassed the switch and nothing!

The two toroids?? both measure 0.5 ohms.

Second half of your instruction i am lost! No idea where to put probes etc….

Edited By mark smith 20 on 28/05/2020 14:31:22

Edited By mark smith 20 on 28/05/2020 14:35:45

[Joseph Noci 1Participant @josephnoci1]

I am trying to help Mark…'nothing' tells me 'nothing'….

I presume the motor did not turn.

Did you measure at the brush terminals? Nothing?

At the rectifier outputs ( the two toroids black wires?) – Nothing?

[mark smith 20Participant @marksmith20]

Sorry, no humming noise and no movement of motor spindle at all.

[mark smith 20Participant @marksmith20]

Where do i put the probes to measure the brush terminals ? One probe on one terminal and one on other ?

[mark smith 20Participant @marksmith20]

There is 240v ac going into the board  measured with the meter but at the other side of the board ,the points that go to the motor brushes there is no DC but 70V AC when measured between those two points ???

But when i measure between the two toroids i get  -250V DC

 

Edited By mark smith 20 on 28/05/2020 14:56:33

Edited By mark smith 20 on 28/05/2020 15:19:02

[Joseph Noci 1Participant @josephnoci1]

The brushes will be under the black plastic cover, each held on by two phillips screws in your picture (below)

Visible is one wire from the PCB , going under the cover to the brush terminal. That is where you need to make contact with the probe.

You said the brushes 'look' fine – are they clearly visible – I can't see from your photos.

In essence we need to establish there is continuity from the mains input all the way through to the brushes.

Maybe my texts are too long and I lose you along the way..

Try this first and then we can return to try the measurements I already indicated, if needed.:

Leave the 'paperclips' in place. With the plug removed from the mains , set your meter to 'diode' measurement mode, as you did before.

Connect one probe to the plug live pin, and one to the neutral pin. With no open circuit you would see between 1.2v and 2volts or so.

That would mean the path all the way, through the cables, diode bridge, inductors AND motor brushes and windings is OK.

If you read open circuit, then there is …an open circuit. NOW – turn the motor rotor a few turns by hand, and measure again. If you get a reading, then the brushes are not making good contact. If no reading then we need to get to the motor brush connections, under those plastic covers.

Joe

Edited By mark smith 20 on 27/05/2020 14:49:38

[mark smith 20Participant @marksmith20]

DID you read that i got -250v DC  when i measured between the two toroids as you suggested??

I get 0.7 V between the live and neutral plug pins.

 

Edited By mark smith 20 on 28/05/2020 15:26:03

Edited By mark smith 20 on 28/05/2020 15:41:18

[Joseph Noci 1Participant @josephnoci1]

Now who's not reading…!!! Sorry…I did not see that you got 250VDC at those two points! The comments went onto a new page and I missed that.

It is sort of good news, but with some confusion…the points across which you measure the 250V DC ( GOOD NEWS) should be the same point that the two motor brush wires are connected to.

Attached a cct as I understand of your PCB ( I have omitted the two black capacitors acros the input and output of the large inductor)

At each of the points marked A-A you should measure the '250V-DC'. If it is present at the two black wires on the toroids, then it must be present at the start of the wires ( on the PCB) going to the motor brushes.

Measure across the toroid inputs and then the toroid outputs to be sure. If you measure 70V at the actual motor wire ends on the pcb , then there is a break in the PCB track, or a wire solder joint there is bad.

[mark smith 20Participant @marksmith20]

Between the two actual motor carbon brushes measured removed from the motor im getting no DC but 106V AC

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