Kenwood Chef A700B sends internet off - UK Vintage Radio Repair and Restoration Discussion Forum

PaulR · 24th Mar 2021, 11:54 am

I fitted a repair kit to my son's Kenwood mixer several years ago. He has just let me have it back as it stopped working. As far as I can tell this was simply because a brush had stuck in its holder.

I have polished up the commutator and removed and cleaned the brush holders, fitted new brushes and it works well. I have never been happy with the way the resistor in the kit fits so I have a "gold" wire wound resistor on order to replace it.

My son mentioned that it sends the internet off when it is used and I assumed that was because of sparking due to the sticking brush. It is still doing it, however. I assume this is actually because of the way the speed regulation works. It is suppressed as per the repair kit with two X2 caps, two chokes and the power resistor across the make and break switch. Is there anything I can do to increase the suppression to stop this happening or is it just something to be put up with when using such an old piece of equipment?

SiriusHardware · 24th Mar 2021, 12:19 pm

Maybe a clamp-fit ferrite on the mains lead either inside or just outside of the unit?

paulsherwin · 24th Mar 2021, 12:40 pm

It must be generating an awful lot of RFI if it's knocking out an ADSL/VDSL connection. I suspect this isn't just a question of suppression, and an undiagnosed fault is still present.

I hope your son has tolerant neighbours!

PaulR · 24th Mar 2021, 1:43 pm

Thanks for the replies.

There isn't really a lot to go wrong with it. It is just a motor with the make/break governor.

I might try shorting out the governor to see whether there is a problem with the motor. The commutator segments weren't burnt at all and the motor seems to run ok.

PaulR · 24th Mar 2021, 2:26 pm

Rather than shorting the governor switch I adjusted the governor itself so that it does not touch the switch when set to full speed.

I started it like that through the lamp limiter with a 100w lamp in it and the internet is fine. There is also no interference on MW. Switching out the lamp also doesn't produce any interference. It occurred to me that the problem might be because the new brushes need wearing in so I have left it running with the lamp limiter as it is rather frenetic on full power.

I did try briefly slowing the motor using the speed control and there was a lot of RF interference so maybe some more suppression would be useful if possible.

Graham G3ZVT · 24th Mar 2021, 3:00 pm

Quote:

Originally Posted by PaulR

I have a "gold" wire wound resistor on order to replace it.

I wonder if the use of an inductive WW resistor in the snubber circuit has formed a resonant tuned circuit and increased the RF radiation?

Probably not, but that's what entered my mind when I read the above.

PaulR · 24th Mar 2021, 3:15 pm

That is an interesting theory. In fact the green resistor I didn't like was a wire wound one on a ceramic core. I bought one 50w new one but that was a little too large. I used it to test it out whilst a got a 25w one. That is metal cased and will screw to the case which is earthed. The replacement arrived at lunchtime but I haven't fitted it properly yet.

I will report when it is back together again.

PaulR · 24th Mar 2021, 5:35 pm

I have fitted the new resistor and replaced the capacitors. They weren't old but had a hard life!.. It has been running on 1/2 speed for 20 minutes now and the internet is still on - phew.

Thanks for the inspiration - it's good to discuss things.

Graham G3ZVT · 24th Mar 2021, 7:36 pm

I forgot to mention, a MW transistor radio makes an excellent site-survey tool in these circumstances.

PaulR · 24th Mar 2021, 9:19 pm

Yes, I found that. I just need to get new cork washers to hold all the oil and grease back now!

G6Tanuki · 25th Mar 2021, 7:07 pm

Good to hear you got it fixed: the old Kenwoods were extremely well-built, rather more like proper catering-grade machines than domestic appliances - but the speed-control I guess could be described as "simple but barbaric" - I remember my mother's one triggered a lovely lots-of-white-dots snowstorm-effect on our old 405-line TV. Fortunately she only used it infrequently!

PaulR · 25th Mar 2021, 7:29 pm

Like so many appliances from that era they seem to be built to last for ever. "Simple but barbaric" is a very good description of the speed controller!

My son and daughter in law use it to make bread and apparently it has to be held down to stop it from dancing across the worktop. They have all sorts of attachments for it including a bean shredder, a sausage maker, a coffee grinder and an ice cream maker. They all get regular use except the bean shredder which significantly looks unused and came in its original box.

24th Mar 2021, 11:54 am	#1
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,233	Kenwood Chef A700B sends internet off I fitted a repair kit to my son's Kenwood mixer several years ago. He has just let me have it back as it stopped working. As far as I can tell this was simply because a brush had stuck in its holder. I have polished up the commutator and removed and cleaned the brush holders, fitted new brushes and it works well. I have never been happy with the way the resistor in the kit fits so I have a "gold" wire wound resistor on order to replace it. My son mentioned that it sends the internet off when it is used and I assumed that was because of sparking due to the sticking brush. It is still doing it, however. I assume this is actually because of the way the speed regulation works. It is suppressed as per the repair kit with two X2 caps, two chokes and the power resistor across the make and break switch. Is there anything I can do to increase the suppression to stop this happening or is it just something to be put up with when using such an old piece of equipment? __________________ Paul

24th Mar 2021, 12:19 pm	#2
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,556	Re: Kenwood Chef A700B sends internet off Maybe a clamp-fit ferrite on the mains lead either inside or just outside of the unit?

24th Mar 2021, 12:40 pm	#3
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,943	Re: Kenwood Chef A700B sends internet off It must be generating an awful lot of RFI if it's knocking out an ADSL/VDSL connection. I suspect this isn't just a question of suppression, and an undiagnosed fault is still present. I hope your son has tolerant neighbours!

24th Mar 2021, 1:43 pm	#4
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,233	Re: Kenwood Chef A700B sends internet off Thanks for the replies. There isn't really a lot to go wrong with it. It is just a motor with the make/break governor. I might try shorting out the governor to see whether there is a problem with the motor. The commutator segments weren't burnt at all and the motor seems to run ok. __________________ Paul

24th Mar 2021, 2:26 pm	#5
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,233	Re: Kenwood Chef A700B sends internet off Rather than shorting the governor switch I adjusted the governor itself so that it does not touch the switch when set to full speed. I started it like that through the lamp limiter with a 100w lamp in it and the internet is fine. There is also no interference on MW. Switching out the lamp also doesn't produce any interference. It occurred to me that the problem might be because the new brushes need wearing in so I have left it running with the lamp limiter as it is rather frenetic on full power. I did try briefly slowing the motor using the speed control and there was a lot of RF interference so maybe some more suppression would be useful if possible. __________________ Paul

24th Mar 2021, 3:15 pm	#7
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,233	Re: Kenwood Chef A700B sends internet off That is an interesting theory. In fact the green resistor I didn't like was a wire wound one on a ceramic core. I bought one 50w new one but that was a little too large. I used it to test it out whilst a got a 25w one. That is metal cased and will screw to the case which is earthed. The replacement arrived at lunchtime but I haven't fitted it properly yet. I will report when it is back together again. __________________ Paul

24th Mar 2021, 5:35 pm	#8
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,233	Re: Kenwood Chef A700B sends internet off I have fitted the new resistor and replaced the capacitors. They weren't old but had a hard life!.. It has been running on 1/2 speed for 20 minutes now and the internet is still on - phew. Thanks for the inspiration - it's good to discuss things. __________________ Paul

24th Mar 2021, 7:36 pm	#9
Graham G3ZVT Dekatron Join Date: May 2010 Location: Greater Manchester, UK. Posts: 18,713	Re: Kenwood Chef A700B sends internet off I forgot to mention, a MW transistor radio makes an excellent site-survey tool in these circumstances. __________________ -- Graham. G3ZVT

24th Mar 2021, 9:19 pm	#10
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,233	Re: Kenwood Chef A700B sends internet off Yes, I found that. I just need to get new cork washers to hold all the oil and grease back now! __________________ Paul

25th Mar 2021, 7:07 pm	#11
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: Kenwood Chef A700B sends internet off Good to hear you got it fixed: the old Kenwoods were extremely well-built, rather more like proper catering-grade machines than domestic appliances - but the speed-control I guess could be described as "simple but barbaric" - I remember my mother's one triggered a lovely lots-of-white-dots snowstorm-effect on our old 405-line TV. Fortunately she only used it infrequently!

25th Mar 2021, 7:29 pm	#12
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,233	Re: Kenwood Chef A700B sends internet off Like so many appliances from that era they seem to be built to last for ever. "Simple but barbaric" is a very good description of the speed controller! My son and daughter in law use it to make bread and apparently it has to be held down to stop it from dancing across the worktop. They have all sorts of attachments for it including a bean shredder, a sausage maker, a coffee grinder and an ice cream maker. They all get regular use except the bean shredder which significantly looks unused and came in its original box. __________________ Paul