Kenwood Chef A701a motor - UK Vintage Radio Repair and Restoration Discussion Forum

Spencervs · 21st Mar 2017, 11:54 pm

Hi guys, I've recently bought a Kenwood chef which I have adored using over the last few months.

Recently, I noticed the dreaded hot electronic smell and a lack of speed control! So I bought a kit of components to repair it. Having removed the motor safely, I replaced the capacitor and two resistors. The speed it fine now. However I can still smell the burning and can see some smoke.

Having read up about carbon brushes, I replaced the ones in the Chef and to no avail. I looked inside and I'm sure the culprit is that there is sparking where the brush meets the motor. Also just above the resistor, there is a switch contact which is also sparking! Has anyone come across this??

GMB · 22nd Mar 2017, 12:16 am

Sparking at the brushes is usually a sign of a burned out segment. This might be more obvious at maximum speed, i.e. that it won't do it. I think replacing the motor is the only hope if that is what it is. Look for a burned mark on the commutator.

I suggest you do what I have done and look out on eBay as people sell broken ones for parts. By far the commonest fault is capacitor failure - and always very spectacular - looking much worse than it is.

I got a broken one for £2.50 and now ours is 100% working like new.

dseymo1 · 22nd Mar 2017, 9:11 am

The sparking switch contact is normal for these, provided it isn't excessive. They have an electroemechanical speed governor, which works by pulsing the motor via that switch. Having said that, that's why the capacitor's there, to suppress the arcing. Perhaps my memory's playing tricks, but shouldn't there be two (or even three) caps?
If there's no severe burning of the commutator,you could try cleaning it by wrapping some fine abrasive paper round it and rotating the shaft by hand (non-approved method due to possible embedding of abrasive dust, but it will be OK in practice).
If all else fails,drop me a PM,and I might be able to find you a motor.

trsomian · 22nd Mar 2017, 9:13 am

Excess sparking at the commutator usually indicates a damaged armature winding, which is usually fatal for the motor, rewinding such a motor is seldom economically justifiable.

There used to be a chap on the east coast somewhere who sells second hand parts for these things, I have had several parts from him over the years; the infamous little plastic pinion on its shaft, on/off switch and other bits

Karen O · 22nd Mar 2017, 5:42 pm

A little while ago I was given a Kenwood blender motor, but I can see no markings like you describe. It has a label saying "Part No 23746" and "D5" underneath. If it's what you need I'll happily donate it.

fetteler · 22nd Mar 2017, 11:53 pm

ISTR there is a mod somewhere that can be done by adding a triac for switching the motor and so stopping the speed regulator contacts from arcing.

Steve.

GMB · 23rd Mar 2017, 10:36 am

Since it already has a triac control I would not expect to see sparking at the switch contacts unless the triac is dead.

Spencervs · 23rd Mar 2017, 11:10 am

Wow lots of amazing suggestions guys! I thought with this Chef the triac wasn't present? If it helps the chat, I can send photos? Is there a way to video and post the sparking?? Perhaps that will be useful in diagnostics. I really hope my kenny doesn't have to go on the scrap heap!!

John M0GLN · 23rd Mar 2017, 11:50 am

Quote:

Originally Posted by Spencervs

I really hope my kenny doesn't have to go on the scrap heap!!

It shouldn't have to, they seem to be quite collectable, a Google search shows sites selling plenty of spares. I changed some components around the motor a few years ago on mine.

John

Refugee · 23rd Mar 2017, 3:24 pm

I would with it unplugged rotate the motor by hand using a wood or plastic tool in the liquidizer drive to make sure it is running free.
Stiff grease will certainly put a lot of load on the motor and it needs to be eliminated.

Our original one got a crack in the mincer drive due to frozen food being put through it.
It had been re-purposed because an absolutely mint one came up for sale less than 5 miles away. It has still got the dust cover with it. The call was for a new one and this nearly NOS one fulfilled the need.

dseymo1 · 23rd Mar 2017, 5:14 pm

Quote:

Originally Posted by Spencervs

Wow lots of amazing suggestions guys! I thought with this Chef the triac wasn't present?

Triac control was introduced for the 900 series, I think.

Spencervs · 24th Mar 2017, 9:16 am

Ah the grease is an interesting thought! It gets really hot which I thought originally could be the resistor but physical resistance could also be the cause I suppose. But would it cause all the sparking at the connectors for the carbon brushes? How would I clean the motor? I'm hesitant to dump it all in meths haha.

Refugee · 24th Mar 2017, 1:26 pm

You can run the motor for a little while and then see if the motor frame is warm.
Rotating the motor by the liquidizer drive is a lot safer and will give you a feel of how stiff the grease has become in the gear box.

fetteler · 24th Mar 2017, 1:31 pm

Quote:

Originally Posted by Spencervs

Wow lots of amazing suggestions guys! I thought with this Chef the triac wasn't present? If it helps the chat, I can send photos?

Photos are good! Especially if they show the presence/absence of a triac

Steve.

Spencervs · 24th Mar 2017, 8:00 pm

Ah the grease in the gearbox- it's not that cos I've re-greased it a while ago. I will take some pictures tonight

Spencervs · 25th Mar 2017, 1:03 am

Ok so here are some photos of the motor with the new components as it is now. some blurry sparking has been captured inside where the carbon brushes meet the motor, and also on a switch contact as you can just about see.

Is the sparking what is causing the motor to get hot to the touch and smell slightly of burning/smoke?

Mike Phelan · 25th Mar 2017, 9:51 am

Sounds like one of the armature windings. Don't let it get too hot and make sure the motor is completely free.

Spencervs · 25th Mar 2017, 12:18 pm

How easy should the motor be to turn? There is some small resistance but not sure if there would be grease inside. Should I just find a new armature winding piece?

TrevorG3VLF · 25th Mar 2017, 10:38 pm

What do you mean by 'where the brushes meet the motor'?
The brushes are inside the motor and connect the motor supply to the rotating commutator and hence the armature windings.
There is always some sparking between the brushes and commutator but if a winding is faulty, then the sparking is much more severe at one position and the armature can be eroded. If this has occurred, then the motor is scrap.
You could measure the resistance between adjacent segments.

A good commutator will be chocolate coloured and will not be appreciably worn. It can be cleaned with white spirit. Do not use emery paper or other grit.

Spencervs · 26th Mar 2017, 8:15 am

Ok, I've made this quick video to show you the sparking. Please tell me whether it's an excessive amount. It is on the communicator and one of the switches.

Having looked at a few YouTube videos, it seems my armature winding is stiff! It doesn't move freely. So I was thinking of taking it out and giving it a light oil. How do I get the spindle though off the top? There's a pin holding it in place and it's tough!!

https://youtu.be/QQp1e2-iRfQ

21st Mar 2017, 11:54 pm	#1
Spencervs Hexode Join Date: Apr 2011 Location: Grove Park, SE London Posts: 382	Kenwood Chef A701a motor Hi guys, I've recently bought a Kenwood chef which I have adored using over the last few months. Recently, I noticed the dreaded hot electronic smell and a lack of speed control! So I bought a kit of components to repair it. Having removed the motor safely, I replaced the capacitor and two resistors. The speed it fine now. However I can still smell the burning and can see some smoke. Having read up about carbon brushes, I replaced the ones in the Chef and to no avail. I looked inside and I'm sure the culprit is that there is sparking where the brush meets the motor. Also just above the resistor, there is a switch contact which is also sparking! Has anyone come across this??

22nd Mar 2017, 12:16 am	#2
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,094	Re: Kenwood Chef A701a motor Sparking at the brushes is usually a sign of a burned out segment. This might be more obvious at maximum speed, i.e. that it won't do it. I think replacing the motor is the only hope if that is what it is. Look for a burned mark on the commutator. I suggest you do what I have done and look out on eBay as people sell broken ones for parts. By far the commonest fault is capacitor failure - and always very spectacular - looking much worse than it is. I got a broken one for £2.50 and now ours is 100% working like new.

22nd Mar 2017, 9:11 am	#3
dseymo1 Retired Dormant Member Join Date: Dec 2007 Location: Shropshire, UK. Posts: 3,051	Re: Kenwood Chef A701a motor The sparking switch contact is normal for these, provided it isn't excessive. They have an electroemechanical speed governor, which works by pulsing the motor via that switch. Having said that, that's why the capacitor's there, to suppress the arcing. Perhaps my memory's playing tricks, but shouldn't there be two (or even three) caps? If there's no severe burning of the commutator,you could try cleaning it by wrapping some fine abrasive paper round it and rotating the shaft by hand (non-approved method due to possible embedding of abrasive dust, but it will be OK in practice). If all else fails,drop me a PM,and I might be able to find you a motor.

22nd Mar 2017, 9:13 am	#4
trsomian Hexode Join Date: Oct 2010 Location: Box End, Beds. UK. Posts: 271	Re: Kenwood Chef A701a motor Excess sparking at the commutator usually indicates a damaged armature winding, which is usually fatal for the motor, rewinding such a motor is seldom economically justifiable. There used to be a chap on the east coast somewhere who sells second hand parts for these things, I have had several parts from him over the years; the infamous little plastic pinion on its shaft, on/off switch and other bits

22nd Mar 2017, 5:42 pm	#5
Karen O Rest in Peace Join Date: Jul 2011 Location: Bridgnorth, Shropshire, UK. Posts: 787	Re: Kenwood Chef A701a motor A little while ago I was given a Kenwood blender motor, but I can see no markings like you describe. It has a label saying "Part No 23746" and "D5" underneath. If it's what you need I'll happily donate it.

22nd Mar 2017, 11:53 pm	#6
fetteler Octode Join Date: Jul 2011 Location: Staffordshire Moorlands, UK. Posts: 1,475	Re: Kenwood Chef A701a motor ISTR there is a mod somewhere that can be done by adding a triac for switching the motor and so stopping the speed regulator contacts from arcing. Steve. __________________ Those who lack imagination cannot imagine what is lacking...

23rd Mar 2017, 10:36 am	#7
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,094	Re: Kenwood Chef A701a motor Since it already has a triac control I would not expect to see sparking at the switch contacts unless the triac is dead.

23rd Mar 2017, 11:10 am	#8
Spencervs Hexode Join Date: Apr 2011 Location: Grove Park, SE London Posts: 382	Re: Kenwood Chef A701a motor Wow lots of amazing suggestions guys! I thought with this Chef the triac wasn't present? If it helps the chat, I can send photos? Is there a way to video and post the sparking?? Perhaps that will be useful in diagnostics. I really hope my kenny doesn't have to go on the scrap heap!!

23rd Mar 2017, 3:24 pm	#10
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: Kenwood Chef A701a motor I would with it unplugged rotate the motor by hand using a wood or plastic tool in the liquidizer drive to make sure it is running free. Stiff grease will certainly put a lot of load on the motor and it needs to be eliminated. Our original one got a crack in the mincer drive due to frozen food being put through it. It had been re-purposed because an absolutely mint one came up for sale less than 5 miles away. It has still got the dust cover with it. The call was for a new one and this nearly NOS one fulfilled the need.

24th Mar 2017, 9:16 am	#12
Spencervs Hexode Join Date: Apr 2011 Location: Grove Park, SE London Posts: 382	Re: Kenwood Chef A701a motor Ah the grease is an interesting thought! It gets really hot which I thought originally could be the resistor but physical resistance could also be the cause I suppose. But would it cause all the sparking at the connectors for the carbon brushes? How would I clean the motor? I'm hesitant to dump it all in meths haha.

24th Mar 2017, 1:26 pm	#13
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: Kenwood Chef A701a motor You can run the motor for a little while and then see if the motor frame is warm. Rotating the motor by the liquidizer drive is a lot safer and will give you a feel of how stiff the grease has become in the gear box.

24th Mar 2017, 8:00 pm	#15
Spencervs Hexode Join Date: Apr 2011 Location: Grove Park, SE London Posts: 382	Re: Kenwood Chef A701a motor Ah the grease in the gearbox- it's not that cos I've re-greased it a while ago. I will take some pictures tonight

25th Mar 2017, 1:03 am	#16
Spencervs Hexode Join Date: Apr 2011 Location: Grove Park, SE London Posts: 382	Re: Kenwood Chef A701a motor Ok so here are some photos of the motor with the new components as it is now. some blurry sparking has been captured inside where the carbon brushes meet the motor, and also on a switch contact as you can just about see. Is the sparking what is causing the motor to get hot to the touch and smell slightly of burning/smoke? Attached Thumbnails

25th Mar 2017, 9:51 am	#17
Mike Phelan Dekatron Join Date: Nov 2003 Location: Near Leeds, West Yorkshire, UK Posts: 4,609	Re: Kenwood Chef A701a motor Sounds like one of the armature windings. Don't let it get too hot and make sure the motor is completely free. __________________ Mike.

25th Mar 2017, 12:18 pm	#18
Spencervs Hexode Join Date: Apr 2011 Location: Grove Park, SE London Posts: 382	Re: Kenwood Chef A701a motor How easy should the motor be to turn? There is some small resistance but not sure if there would be grease inside. Should I just find a new armature winding piece?

25th Mar 2017, 10:38 pm	#19
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	Re: Kenwood Chef A701a motor What do you mean by 'where the brushes meet the motor'? The brushes are inside the motor and connect the motor supply to the rotating commutator and hence the armature windings. There is always some sparking between the brushes and commutator but if a winding is faulty, then the sparking is much more severe at one position and the armature can be eroded. If this has occurred, then the motor is scrap. You could measure the resistance between adjacent segments. A good commutator will be chocolate coloured and will not be appreciably worn. It can be cleaned with white spirit. Do not use emery paper or other grit.

26th Mar 2017, 8:15 am	#20
Spencervs Hexode Join Date: Apr 2011 Location: Grove Park, SE London Posts: 382	Re: Kenwood Chef A701a motor Ok, I've made this quick video to show you the sparking. Please tell me whether it's an excessive amount. It is on the communicator and one of the switches. Having looked at a few YouTube videos, it seems my armature winding is stiff! It doesn't move freely. So I was thinking of taking it out and giving it a light oil. How do I get the spindle though off the top? There's a pin holding it in place and it's tough!! https://youtu.be/QQp1e2-iRfQ