Kenwood HB720 repair

Our Kenwood HB720 hand blender suddenly stopped working. The punchline of this post is that inside its excruciatingly-difficult-to-dismantle mechanism (i.e. never intended to be repaired), it includes a fuse, which had blown.  This post will be updated to give the details about how to take the machine apart, and whether I managed to reassemble it after replacing the fuse.

So, if “the motor is broken” on yours, it may just be the fuse that has blown.

One sign that the fuse is probably blown is that a diode test with +ve on phase, -ve on neutral shows open circuit when the Turbo button is pressed (this button bypasses the speed controller, and connects mains power via a bridge rectifier to the DC motor).


Tricky. There are a couple of videos purporting to show how to dismantle it, but I reckon they both are filmed after the unit has been dismantled and reassembled.

First remove the drive-end cover.  This is held in place by three  hooks on the inner plastic part, that engage with square holes on the cover.  One is above the ejector wedge on the side without the number stamped on it. The others are 120 degrees round from that. You might be able to get this cover off just by pulling very hard, but otherwise probe with a small screwdriver(s) to push the hooks inwards and disengage them.

The inner part is glued or welded in to the body.  This thing is a prick to get out. I attacked it with a screwdriver and a scalpel, and still it looks fairly munted.

Carefully prise off the speed control knob at the cord end.  This reveals 4 screws, to be removed. Turn over the plastic circle with the cog and undo the 2 screws to release the cord clamp. Slide the knob and clamp up the cord.

Now push on the plastic tray holding the circuit board, pull on the motor shaft to remove the motor + speed control assembly.


So here’s the speed controller board

The fuse is inside black heatshrink “FR-H TUBE 125C”.  It is soldered to the board.


The blown fuse


The speed controller

A strange thing is that the fuse is rated at 1.6A, while the machine is nominally 700W.  Unless I’m missing something, 3A at 240V is 720W, so either Kenwood is lying about the power rating, or the fuse rating is too low?

I replaced the fuse with a piece of wire, because I’m not planning to open this up again.


Schematic (polish)

Another set of photos about dismantling and assembling HB720.  Pretty good,  the inner and outer drive-end covers are shown still connected together. I doubt it is possible to remove them in this state.


5th Anniversary of Christchurch Quake

Today is February 22nd, the 5th anniversary of the (first of many) earthquakes that devastated Christchurch.

There has been plenty written about the big picture so I’ll add a few words about the little picture I see around here.

I’m still in the same house I was in on that day.  It was repaired over five months in the first half of 2014 (thanks to the guys from Clive Barrington Construction – it was worth the wait to get you).    Due to some quirk of geology and construction, it stood up pretty well compared to our neighbours.

Lets talk about them…

Three  sections to the North, the retaining walls have been slowly repaired over the last 8 months or so. I hope a house will start going up there soon, and eventually the lovely family who lived there will be able to return before our children leave home.

Two houses North, the house is clad in its second lot temporary building paper.  The house will eventually have to be demolished. The people who live there have finally got fed up with waiting and are looking elsewhere.  I don’t blame them.

Our neighbour to the North still lives there, still waiting for the partial rebuild, partial repair that is the latest word on what will happen.

The two houses to the South are both unoccupied, and becoming more and more derelict. They will both have to be demolished.

On the other side of the lane, the small cottage has been repaired, the other two houses are liveable but not repaired yet.

So don’t tell me to move on, or scold me for being negative and tell me that things are pretty much sorted – they have hardly started, and I’m not looking forward to the noise, dirt and disruption that is yet to come.



Nature abhors a vacuum

Repair of Kenwood FP481 Food Processor

This is a follow up to my previous post.

Thanks to need a part, I got the spare parts I needed to repair the food processor. The price was enough to make me wince! : Upper drive belt $19.95, Upper cog $18.95, P&P $7, (+ Hand Blender geared lid $19.95).  But a combination of bloodymindedness and marginally OK economics meant I went ahead with this anyway.


Out with the old and in with the new.

The drive belt is a direct replacement, but the toothed pulley is made for a shaft with 2 flats on it.


Old pulley used nut to stop it spinning.

The new pulley lacks the square nut cage, so I can’t just drill it out for the round shaft.  I’ll grind the shaft down instead.


Now lets see if I can remember how this all goes back together.


Reattach the motor to the top plate


Attach the interlock mechanism


And the interlock circuit board

Then reattach the on/off/speed/pulse switch.



The final step is to put the bottom of the case back on and I’m back in business.


Crappy Kenwood plastic gears!

Expensive (yet crappy) Kenwood FP481 food processor strips its drive belt and gears when the chopper inevitably gets jammed.

I’m not sure what happened first.  Either the belt started to lose its teeth, then the gear started slipping and ground its teeth off.

Worn drive belt

Or the gear wore out first, then ground the teeth off the drive belt.

worn Kenwood FP481 upper sprocket

I’m currently trying to get replacements that aren’t prohibitively expensive.  To make things harder, Kenwood changed the design of the sprocket slightly so current spares are not directly compatible.

On to the Kenwood HB720 tri-blade stick blender with mini chopper attachment.

Inside the chopper lid there is a single plastic cog on a metal shaft that drives 3 planetary gears.
The cog has split, maybe after the shaft started slipping and heated up the plastic, but who knows. This cog needs to be stronger as it is driving 3 cogs. Or there should be a proper clutch mechanism that avoids catastrophe when the chopper inevitably jams.


This is clearly not meant to be serviced.  I’m supposed to throw it away and spend $27 on a new one.

Power consumption hall of shame

Some appliances consume quite a bit of power even when they are switched off. In the following table “soft off” means that it is turned off using the remote control or soft button. “switch off” means it is turned off using the (apparent) on/off switch.

Appliance On Soft off Switch off
Sharp TV 145 24 24
Samsung 22 inch TV 45 9
DSE DVD 14 10 0
Sony DVD 9 1

The so-called power switch is not always what it seems – for instance the Sharp TV switch just stops the TV being turned on using the remote, but power consumption is still 24W even in the off position.

Stupid serving suggestions.

Griffins suggests that you should serve two macaroons, one with a bite taken out of it, along with half of a miniature fresh coconut:

Macaroon "serving suggestion"

Tip top suggests that you should serve icecream by placing a ball of it on the table, and inserting two whole vanilla beans to look like a  moustache.  Then draw a red beret on top of it.

ball of icecream with vanilla beans

Tip Top serving suggestion

A Better Microwave Oven UI

What should a power user’s microwave oven interface look like? Not like My panasonic one

A sketch of a simple user interface for a microwave oven.

Microwave UI

Two vertical touch strips, one linear power 10% to 100%, the other logarithmic time.  Touch the power to set power,  touch the time to set time and start the cooking.  The controls have lights behind to show current power setting and remaining time.  Any time, just touch either control to change the power, or increase or decrease the time. + – nudge button on the time