Author Topic: Saving my Sharp microwave oven - Part 1  (Read 8401 times)

0 Members and 1 Guest are viewing this topic.

David HK

  • Hero Member
  • *****
  • Posts: 512
  • Country: hk
  • Hubei Province China - wind farm control room
Saving my Sharp microwave oven - Part 1
« on: October 25, 2011, 12:26:41 AM »
This article may be of interest to forumites.

I own a more than 20 years old Sharp microwave convection oven model R-9H10. It has a very large cavity and has given good service.

In late September 2011 it finally failed and after doing a bit of checking I concluded that the front panel touch membrane selector buttons/ switches/keypad had failed. Pressing any selection failed to produce an operation.

I called in a Sharp technician and he duly confirmed that the membrane switch pad was gone forever and that spares were no longer available. The technician is very experienced with microwave ovens made by Sharp and he did me a favour by checking over the rest of the machine which was diagnosed to be in good working condition. Finally he helped me dismantle the entire key pad into its various parts and this included separating the membrane keypad from the main plastic piece housing all the various components.

I was determined not to waste money and throw this magnificent machine on the scrap heap and so I have made up a replica key pad to perform the same functions.

This is how I did it.

I occasionally use Express PCB to design PCB’s with top and bottom circuits so I am familiar with the operation of the software.

I measured the length and breadth of the membrane keypad and used those dimensions to create a new board with the software. This is shown as a yellow line – in this case a rectangle. Next I copied exactly all the key configurations shown on the front panel – Compu cook, 140 C, Start and so on.

Eventually I was able to print out an exact copy of the keypad outline and check that I had named everything correctly.

Next was the insertion of the shape representing a micro switch taken from the software library – all 28 of them – and located in the centre of each switch.

At this point I was ready to follow the traces on the upper and lower plastic sheets that are glued together to make the membrane keypad. The circuit can be sketched out with a pencil and paper but I prefer to lay it out directly in the software as I go.

I discovered that 4 tracks ran under and 7 ran on top. There is actually a 12th track that runs around the entire circuit board and does not touch anything. I have no idea what this is for. Going back to the 4 and 7 numbers means that they produce 28 switch positions when multiplied. This matches the same number on the keypad.

I eventually worked out how the alignments were configured and the only difficult parts were lines that occasionally crossed.

One interesting thing about this keypad is that none of the lines on either side cross over each other on the same side. There are no ‘through holes’ or ‘via’s’ because of the nature of the plastic sheet.

So far so good and the next step was to take close up digital photographs of the tracks on both sides of the plastic membranes.

The next step was to separate the two plastic sheets and I found the best thing for this was a hair dryer. I tried acetone and paint thinner but this was not very effective and merely diluted the glue. A good heat build up and slow pressure applied to the separating sheets did the trick eventually but I did wreck the circuit in the middle of the membrane area. There was still some cleaning to be done on the plastic housing and the best item I found for this was methylated spirits, a kitchen paper towel and some

Fortunately all was not lost. The next step was Microsoft Word and a multimeter set on resistance setting and starting at Pin 1 (or whatever you decide to name it) I then followed the tracks I had already made and wrote down the function as I came across them.

Pins 1 to 4 on the underside on the sheet each contain seven function names. Pins 5 to 11 on the topside sheet contain 4 function names. Remember the mathematics:-  4 x 7 = 28.

Pin 1   -  Compu cook, 40C, 150C, Med high, 130C, 70C, 160C =   7 items

Pin 2 -    Sensor cook, 200C, 220C, 230C, 180C, 250C, Med     =   7 items

Pin 3 -  One touch reheat, Convec, Grill, Slow cook, Low mix bake, High mix roast, Med low defrost    =   7 items

Pin 4 -    Easy defrost, High, Stop clear, Instant cook start, Memory, Low, Auto start clock    =   7 items


Pin 5 -    Compu cook, Sensor cook, One-touch reheat, Memory                              =   4 items

Pin 6 -    Low, Med low defrost, Med, Med high       =   4 items

Pin 7 -    Convec, 40C, High, 180C,             =   4 items

Pin 8 -   Low mix bake, 70C, 200C, Auto start clock,    =   4 items

Pin 9 -    Easy defrost, Grill, 130C, 220C         =   4 items

Pin 10 -    Slow cook, 230C, Stop clear, 150C       =   4 items

Pin 11 -   High mix roast, 250C, 160C, Instant cook start   =   4 items

The next step was to convert the above details into a matrix which produced this:-

   Pin 1   Pin 2   Pin 3   Pin 4
            
Pin 5   Compu cook   Sensor cook   One touch reheat   Memory
Pin 6   Medium high   Med   Med low defrost   Low
Pin 7   40C   180C   Convec   High
Pin 8   70C   200C   Low mix bake   Auto start clock
Pin 9   130C   220C   Grill   Easy defrost
Pin 10   150C   230C   Slow cook   Stop clear
Pin 11   160C   250C   High mix roast   Instant cook start

From the matrix it is easy to use a multi meter to select two pins and observe the needle move so that the function of that switch can be checked on the matrix table.

By now I had the circuit set out with nice thick lines, the silk screen showed an exact replica of the key functions so I wanted a do another cross check. This was done by using an AutoCAD programme and inserting a BMP photograph of the key pad. The lines were traced out again – green for bottom and red for top  - and after tidying up this was printed for a like for like comparison with the Express PCB printouts. They matched.

I subsequently placed an order for two key pads (minimum order) and should be able to solder in the 28 micro switches on Saturday 29th October 2011. I already have the new connector wires and I have also made a plastic shape to fit over all the micro switches to absorb their thickness – around 3mm not including the push button itself.

Everything has been meticulously cleaned including the machine itself.

David HK

  • Hero Member
  • *****
  • Posts: 512
  • Country: hk
  • Hubei Province China - wind farm control room
Re: Saving my Sharp microwave oven - Part 1
« Reply #1 on: October 25, 2011, 12:45:38 AM »
My attachments did not go into the first post so I will finish off with this text and try one JPEG photograoh.




Regards,

David in Hong Kong

ghurd

  • Global Moderator
  • Super Hero Member Plus
  • *****
  • Posts: 8078
Re: Saving my Sharp microwave oven - Part 1
« Reply #2 on: October 25, 2011, 12:58:15 AM »
Astounding effort!

Great job Dave!

G-
www.ghurd.info<<<-----Information on my Controller

David HK

  • Hero Member
  • *****
  • Posts: 512
  • Country: hk
  • Hubei Province China - wind farm control room
Re: Saving my Sharp microwave oven - Part 1
« Reply #3 on: October 25, 2011, 01:18:19 AM »
This is what my story is all about - two plastic sheets containing 28 switches and the difference between throwing what has been  a good machine away and buying a new one, or, attempting a repair that should make it work as it did on day one.

The weakest point on most microwaves is the keypad - especially the plastic membrane type. I failed to mention that after separating the two plastic sheets it was very easy to spot the broken tracks with a good magnifying glass.

4215-0

regards,

David in Hong Kong


rossw

  • Hero Member
  • *****
  • Posts: 845
  • Country: au
Re: Saving my Sharp microwave oven - Part 1
« Reply #4 on: October 25, 2011, 01:26:22 AM »
This is what my story is all about - two plastic sheets containing 28 switches and the difference between throwing what has been  a good machine away and buying a new one, or, attempting a repair that should make it work as it did on day one.

The weakest point on most microwaves is the keypad - especially the plastic membrane type. I failed to mention that after separating the two plastic sheets it was very easy to spot the broken tracks with a good magnifying glass.

We have, somewhere, the version prior to yours. Those ones were particularly good - they'd take a larger container than most of the modern machines.

Still... I was going to comment that a good number of years ago I was asked to fix a rare bit of scientific equipment. It too had a stupid flexible PCB like that that had given up.
The thin plastic backing wasn't suitable to even attempt to solder a strap to.
I wasn't so butcherous as to use a wire staple through either side with a link between, but I used a high-silver content paint that was (in the day) used to connect to (and repair) foil tapes as used on windows for alarm systems. Applied with a small paintbrush, it was good enough to repair the tracks for several years operation and may still be going.
Another abused ex-moderator who's made the move to http://www.otherpower.com.au where DNS works, admins do stuff apart from randomly deleting other peoples posts and sigs, and people are nice.
JW: QUIT EDITING MY SIG!

David HK

  • Hero Member
  • *****
  • Posts: 512
  • Country: hk
  • Hubei Province China - wind farm control room
Re: Saving my Sharp microwave oven - Part 1
« Reply #5 on: October 25, 2011, 03:34:05 AM »
I shall try to insert an Excel file showing the Matrix table.

* Microwave matrix table.xls (13.5 kB - downloaded 317 times.)

Lets see if it works?
« Last Edit: October 25, 2011, 05:47:30 AM by Bruce S »

MaryAlana

  • Hero Member
  • *****
  • Posts: 1200
Re: Saving my Sharp microwave oven - Part 1
« Reply #6 on: October 25, 2011, 08:48:15 AM »
If memory serves me that outside track was a static ground circuit and connected to the metal frame.

Norm

  • Hero Member
  • *****
  • Posts: 1847
  • Country: us
  • Ohio's sharpest corner
Re: Saving my Sharp microwave oven - Part 1
« Reply #7 on: October 28, 2011, 03:20:08 PM »
I also have a Sharp microwave oven Model R-139-RW, manufactured in March 2002.
No trouble with that yet....but the display doesn't light up.....No problem there tho',
Good old LED flashlight shining at an angle lights up the display most of the time I
really don't need it anyway.....most things like, I just push  baked potato button twice and
leave it to the sensor and the baked potato comes out perfect,  rice button for oatmeal
and I watch it rise to max height in the bowl and remove......beverage button once to
reheat a cup of coffee ,twice for a really hot cup of water.....etc.

If it ever gets to the point like yours .....guess I'd just salvage parts.

   But nevertheless I'm in awe of people that can do what you did...
Excellent work  David HK. !
Norm.

chunte

  • Newbie
  • *
  • Posts: 1
  • Country: my
Re: Saving my Sharp microwave oven - Part 1
« Reply #8 on: February 04, 2015, 08:27:42 PM »
Hi David,

Thanks for this write-up. For me, my stop/reset button just stopped working and thanks to your efforts, I used an external switch wired to the pins 4 & 10 of the board. At least for now, I can still get access to it until the next button fails.

Did you printout the entire PCB and paste together your own flexi-circuit? Really curious how you did it and if you still happen to have the PCB files you made?

Warm regards,
CT


Mary B

  • Hero Member
  • *****
  • Posts: 710
Re: Saving my Sharp microwave oven - Part 1
« Reply #9 on: February 05, 2015, 03:21:34 PM »
Necro thread from 2011...

LFO

  • Newbie
  • *
  • Posts: 1
  • Country: au
Re: Saving my Sharp microwave oven - Part 1
« Reply #10 on: December 16, 2016, 05:06:57 AM »
Yes indeed ... this thread is as old as time itself  ;D

And I joined and I am posting to thank David and to state that also my Sharp Carousel is now working again.

The usual story: key pad faulty, nowhere to buy a new one and a unit, a microwave AND convection oven that is all good but for the silly little skin or key pads.

Well, inspired by David HK and reading his matrix noticed how EASY it could be if just using tiny push button switches.
And I managed to get some from my bag of recycled goodies to make a "proof of concept". And worked.

There were some differences on the matrix and their values, my Stop/Clear was pin 4&5 and that is the first action you need to input after restoring power. NOTHING will work until Stop/Clear.

Basically I removed the old key pad, made a photocopy, glued the copy back, glued the switches, solder the wires, reconnected to the connector on the PCB.
Once is all good up and running I will put the old keypad back for aesthetics and it will look as good as new ... well, not that good but it will work as good as always.

I ran out of switches so I bought a batch of 100 from eBay. That will complete ALL buttons. Also I will trim the key pad as the film connector is no longer useful, I only want the shiny front for looks and strength.

For the pins your configuration, as it was my case, is slightly different to David's. What it exactly the same is the fact that the first 4 pins in the PCB (labeled, from top to bottom) are 1 to 4 and 5 to 11 the others.

So this is my story, inspired by David and his post. Hope mine is equally useful.

10133-0
This shows basic layout. Ain't pretty but worked.
10134-1
It's alive!!!! Convection mode set and ready. Not finished but getting there.
10135-2
This will be the new look. As new  ;)