Repair.IT – Kleenmaid TO500X Electric Oven – again

This is a followup to the previous article on the Kleenmaid TO500X Designer Multi Function Electronic Timer Oven.  Remember that after the repair, it was working, but after baking a set of frozen pies on one weekend, the next weekend – it stopped working again.  The symptoms were different this time.  The oven lights inside will work, but no heating or fans would operate.  I thought at first that it was the thermostat, since this controlled the power to the heating elements in order to turn them off to maintain a set temperature.

I switched off the power, and checked that the thermostat was in fact … working, just like last time I checked.  Ok, so scratch that idea – what else could be wrong.  Eventually after some thought and research, I was reading the oven operation manual, which suggested that on some models, there was an oven door switch which would cut the heating if the door was opened.  Yes, this oven did have a door switch, which used to cut off the heating when the door opened, but I remember that recently it had not been stopping the heating.  There is a red indicator light that shows when the heating elements are on, and in the past – this went out when the door was opened, but in the last few months, it seemed to not go out.  Maybe this could be the reason.

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So, open up the housing and locate the door switch that was on the left side, check for continuity, and nothing – even when the button was pressed all the way.  This had failed so checking for a replacement – Metalflex MS-385 seems a common part, but this one was shaped differently.  The local oven parts stores didn’t seem to show this as a spare part – so maybe I can just bypass it, like I did with the relay.

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After I had written the previous article on this oven, I remembered reading that this particular model would disable the power if the clock was not set – as a fail-safe.  By applying the power and setting the clock, I could hear a click from the clock area.  Perhaps the relay was now being turned on.  But then – how to explain the previous problem?  Unless the door switch had decided to become intermittent, and sort of arc’ed over – maybe the timer electronics detected this as a fault and cut the relay.

I had tested the clock board and controller out of the housing and had not been setting the clock, so the relay would not have been turned on.  Bypassing the relay would allow the power to be available independently, so maybe the relay is working again, after a power reset.  To test this hypothesis, I decided to remove the bypass on the relay and just have a bypass on the door switch.

I reassembled the door switch mechanism and then closed up the oven, and went and replaced the fuse that I had pulled out in order to remove power to the oven.  The oven clock was now blinking and after setting the time – a couple of seconds later, I heard a click which could have been the relay turning on.  I used the control to turn on the light, and the light came on – fantastic.  Selecting the fan, and yes – the fan would spin up.  Next, turn the thermostat, and the thermostat indicator light came on – meaning that power was being applied through the thermostat.

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Well that is good, I have a working oven again – except that the door switch is no longer operational – but it was an optional feature anyway, which helped for safety – but most of these ovens don’t have one.  It looks like this oven is now repaired, again – and hopefully for good.  In the meantime, I will see whether I can locate a suitable replacement switch to restore its full function.

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Rectify.IT – Kleenmaid TO500X Designer Multi Function Electronic Timer Oven

One day, my son turned on the electric oven to bake something for lunch.  I only found out when I got home that the oven had stopped working.  It seemed that he turned on the oven and after a short time, there was a sound, and it went dark, with only the clock showing.  This oven is a Kleenmaid TO500X which was quite expensive when we bought it back in 2007, and a few years later, Kleenmaid went out of business only to be resurrected after that.

With the digital clock working, it meant that it was getting power, but none of the other controls, such as oven light, fan, grill – even the thermostat light was dark.  When I got around to it, I turned off the oven power at the switchboard, and pulled out the oven – removed  a few metal panels so that I could inspect the inside of it.

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Typically what usually happens is that the thermostat fails, so I had been checking on prices of thermostats.  Anyway, with the covers off, I could check that the thermostat was – surprisingly ok, by turning the knob to any temperature, the contacts show a connection – which it should if it is working.

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I decided to check the heating elements anyway, and each element had a measurable resistance meaning it should be functional.  I couldn’t see anything else that might be wrong, so closed it up and went to do more research.  After some further time, as in days, I came back to the oven, to check if the thermal overload had triggered.  I found the device screwed onto the rear fan mount, but it showed continuity – and anyway, it would only be a problem if the thermostat had failed in the on position and caused overheating – which it didn’t have time to do.

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Back to the drawing board – so anyway, I woke up one morning and realised something that had been staring me in the face – this multi function over has a timer switch that can cut the power after a set time – I use it all the time when cooking frozen pies, so that I don’t overcook them, as in – burn them to a crisp.  Sure enough, after opening the oven again, the clock timer module has a board on the back with a relay, where the relay contacts control power to the thermostat – now we are getting somewhere.

Removing the clock timer module is complicated, by first removing the thermostat and the control switch – but the hard part was removing the front knobs which I worked out, just need some brute force.  After that the assembly could be removed, then the clock timer module removed from the metal frame.

Removing the circuit boards from the module was also a bit of a job, would be handy to a lot more hands, but eventually it came out.  I checked the components and worked out that the relay was driven by a signal going to a PNP transistor, and eventually after applying some power (albeit carefully) confirmed to my satisfaction that there was no power going to the relay.  I had earlier confirmed that putting 12V onto the relay allowed it to switch and I confirmed that the contacts were closing correctly, hence the relay is good – therefore it was not getting a signal to turn on.

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Debugging it further would require removing the display module in order to work out what was wrong with the timer.  The display has about 20 pins, being a vacuum fluorescent display – which is not an easy job, as I found that my desoldering station wasn’t heating correctly.  So, to fix this, I decided to just bypass the relay – effectively by connecting the contacts to make it think that the relay was on.  The relay contacts are Faston connectors and I remembered having a piggyback adapter in my stock of parts, so after checking a few boxes, found my little adapter.  It plugs into one terminal and allows two cables to plug in – the ones that originally went to each relay contact, now go to this adapter.

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After doing this, I started reassembling the control panel, putting wires back on – in the correct place which is why I usually take photographs of anything that has lots of wires.  To my piggyback adapter, the red and orange wires are connected – which originally was to the relay contacts.

Then the final test, was to turn the oven power back on, and voila – the oven now works.  I checked that the internal light came on, that I could choose heating modes and more importantly, if I set a temperature, the thermostat light shows that it is heating, so all good, except that we have lost the timer function – not a big problem.  A replacement timer module would cost almost $500 which is already close to the cost of a new electric oven.  The moral of the story, is that sometimes a repair only has to make the device work again, and if we accept that some functionality is lost, then that is ok.

Of course, I could have spent more time to actually determine the cause of the failure – but we needed a working oven, and adding this $2 part made it work.

Replace.IT – Upper fan for Antec 1100 computer case

I am a little down with the flu, so sitting at home, it is always a good idea to do some writing, or is it blogging – to clear the backlog of R.IT articles.  The Antec 1100 is a great computer case, since it has lots of fans, and space for hard disks, and lots of expansion slots.  That’s a lot of lots – right.  It had started its life as a case from my scrypt (think – cryptocurrency) mining computer, and was eventually repurposed for my VMware ESXi server.

My ESXi server needed six hard disk drives so this case was ideal for it. After a couple of years of operation, I started hearing a bit of rattling sounds from the server which would come and go.  Eventually I noticed after removing the side panel, and by looking up, that the top exhaust fan, was sometimes stopping and if it would spin, would spin with a wobble or slight rattle.  This was the cause of the sound.

The fan was a 22cm fan, but it was a slightly longer shape – and checking on some forums found that others had similar problems, but had replaced the fan with a standard 22cm computer case fan. I found a Bitfenix 22cm case fan from a local supplier who had it in stock, so bought that one.

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Here is the original fan from the Antec 1100 case. The mounting holes are not as standard as I thought.  When I compared it with the Bitfenix fan, I found that the Bitfenix followed the standard mounting radius and that the Antec fan, had a slightly smaller radius.  After some consideration, I noticed that there were other spots where mounting holes could be available, so used a 4.5mm drill to enlarge the holes adjacent to the standard mounting holes.  It is a bit hard to describe, so here are a few photos.

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This shows the new holes nearby, and the next one is a closeup to clearly show the new mounting hole that is away from the corner.

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So, after this, it should be a small matter to reinstall the fan, however since the server was still running, I decided it would be best to shut it down to make the job easier.  I don’t want to accidentally drop a metal screw onto the motherboard and cause a failure to occur.  Another Replace.IT done.  Now what should I write about next, maybe something of an electronic nature – except those haven’t come up very much lately.

 

Repair.IT – Air Compressor

Some months ago, I needed to paint the wooden deck in my backyard – yes, the one that I built – did I write about it? Anyway, the oil that I used was starting to wear off. A colleague from work suggested that I use a spray gun to make the job go faster which I thought at the time was a great idea. I had already been asking around for a new oil to buy, but the final word was that since we had already used the Cutek oil, that we should continue with that oil.

My colleague had lent the air compressor to another colleague, who in due course finished with his work, and I was able to get the compressor, a long coil of air hose, and a spray gun attachment. On the next available weekend, I hauled everything to the backyard, connected the power to the compressor, and switched on. At this point all I heard was a slight clicking sound coming from the compressor, so switched off. Switched on again, and still the clicking sound, which doesn’t quite sound like a motor turning, but more like a stalled motor.

I shut the power off, then could see the rotor through the grill and could turn the rotor with a long screwdriver, so that means that the motor hadn’t siezed up.  After a bit of head scratching, I decided to open up the cover to expose the motor. An air compressor is essentially a motor that turns a compressor that pushes air into a container until it bursts – or actually, until a pressure is reached whereby the motor is switched off before bursting point.

The motor is just an average ac motor, usually one that is either a capacitor-start motor or a capacitor-run motor – which means that if it doesn’t work, usually it is because a capacitor has failed. So essentially, this capacitor failed between its last job and in transport to my home – what luck. So, opening the cover should allow me to see the capacitor, remove it for checking, and then obtain a replacement.

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As Murphy would have it, part of this was easy and also not easy. The capacitor had some hard black plastic foam glued to it, to stop it from rattling against the case, but the foam had hardened to be almost rock-like – it had dented the side of the capacitor, and as luck would have it, has also covered the part that shows what size the capacitor should be. I measured the capacitance and it was very small, almost unmeasurable whereas I would expect something in the 10-30 uF.

I then used a hacksaw to cut the black foam, and eventually exposed the label enough to show that it is a 35uF capacitor, which was also not an easy one to find. After some time, I decided that I could get a 30uF and a 4.5uF and connect them in parallel, to get 34.5uF which should be close enough, since most capacitances are +-5%.

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Here is my replacement capacitors wired together.

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And now, here they are mounted on the motor frame, which fortuitously had mounting points for two capacitors – great.  Once wired in, and cover replaced – switch on, and the sound of… a loud compressor running, ok – so pressure is not increasing and air coming out the bottom – the drain bolt needs to be screwed out to close the drain.  Try again – and finally, pressure increasing – and eventually, yes – it stops.  Great – another Repair.IT done and can get back to spraying some decking oil.

Repair.IT – Table Tennis Table Support Leg

I was at my local community centre before Easter. They have a number of table tennis tables which get pulled out regularly (almost daily) for people to play table tennis. With all of the use, and sometimes heavy hands, the tables are quite worn and have a few faults. One in particular had a broken support leg, which made it unusable. I had a quick look at it and thought that all it would need is a few brackets to fix the rolling support leg, and it could be as good as new.

I had a look at what Bunnings had to offer and spoke to the community centre about it and offered to fix it for the cost of the parts, which I estimated to be about $30-40. Then it was a matter of getting the parts, then on Thursday last week, I was able to get the leg removed to bring home where I can do the repairs.

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Here is the support leg removed from the table and separated into its various parts, mainly removing the wheels. The top section was welded but this is what had broken.

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A T shaped mending plate was the right size, two of these, one on each side, then a couple of right angle brackets for support. The metal is quite thin on the leg, only 1mm, so I had some 40mm square hollow steel section in my garage, so cut off about 30cm of it. This reinforcing tube which is 2mm thick would fit inside the horizontal leg, but because it is a bit smaller than the inside, would need some spacers to raise it to the top of the leg.

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Then additional spacers for the side, since I wanted to get it more or less in the middle of the hollow leg.

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Here I have fastened the reinforcing tube with four Tek screws. Due to the thickness of the tube, I decided to pre-drill 4mm holes where I would install the Tek screws for the right angle brackets.

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I decided that I should clamp it all together and mark out the holes for the mending plate for both sides. The drilling could then be done easily on my milling machine than with a hand-held drill.

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It was a matter of fastening a lot more Tek screws, and I ended with a leg that is much stronger than the original – maybe a bit of overkill, but not bad for less than $40 in parts. I need to wait until after Anzac Day for the community centre to open before I can install the leg and fasten a couple more screws, and also replace a number of nuts and various bits that were also missing.

If I didn’t help them with this, they would probably have to spend many hundreds of dollars on a new table which is probably not as good as the repaired table. They have some more tables for me to look at too!

Repair.IT – Overheating Presario SR5120AN motherboard

Remember two and a half years ago, approximately, I repaired my Compaq Presario SR5120AN motherboard which had a number of failed capacitors?  Ok, it was some time ago, so here is the link.

https://j0hn88.wordpress.com/2014/12/22/reveal-it-faulty-capacitors-on-presario-sr5120an-motherboard/

At the time, five capacitors had failed, but there were still four others of the same brand and size on the motherboard. I checked them with an ESR meter and they all passed. Fast forward to a month ago – I noticed that my computer cpu fan was getting louder, sometimes normal then suddenly high speed and this kept happening. I ran a utility to check the CPU temperature and it was …  99 degrees, wow! No wonder the fan was on turbos a lot of the time.

I shut down and took the computer apart to reveal the motherboard.

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Two of those same original capacitors were showing the symptoms of failure – see the bulging top and black spots. After some effort, I was able to remove these two capacitors, then replace them with the ones in that little bag – I originally bought ten of these 1800uF 6.3V electrolytic high temperature capacitors. I checked the remaining two on the board and they check out fine.

So, reassemble the computer, and power on – leave it on for a while, and I can see that the CPU temperature is sitting reasonably stable at about 80 degrees. This is still quite hot and would appear to be still abnormal. Since I still have three spares left over, why not just replace the remaining two capacitors and be done with it.

That is what I did – took out the other two capacitors, replaced them with new ones. While I was doing this, I checked the capacitors with my ESR meter, which showed that these two were still ok, but anyway I have new ones in the motherboard now. Once the computer was up and running again, leave it for a while and then it was looking good so I decided to run the Passmark Performance Test, which stresses out the computer.

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This is what the CPU and graphics card temperatures were during the test and then the cooldown period afterwards. The CPU maximum went to about 93 degrees but then back down and sitting stable at 54-60 degrees. This is amazing and shows that even though the ESR meter indicated that the capacitors were ok, replacing them reduced the average temperature dramatically. Why is that – maybe the capacitance has changed? Wait, I can check this!

Just over a year ago, I had bought from eBay, a Mega328 Transistor and component tester. I can connect the parts I have removed and compare with new parts.

These two are the failed capacitors. They appear to be back to back diodes with differing forward voltages.

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Here is a new one – my final remaining capacitor. The value is 1829uF, ESR is good, with Vloss of 2.5%.

Here are the two apparently good ones that I replaced. These also appear to be good as far as the tester is concerned, however replacing these two also brought down my average temperature of the CPU. Why? I don’t really have an answer for this, but maybe someone has.

Right now as I am writing this, my CPU temperature is sitting at around 80 degrees, with CPU load at about 85% since my antivirus scan has been running for some time, but certainly nowhere near the 99 degrees at idle that it was a month ago. It has been a few weeks now, and all seems to be well.

Remake.IT – Raspberry Pi 3 with 7″ Touch Screen and housing

A while ago, I bought a couple of the new Raspberry Pi 3’s and at the same time, bought a 7″ touch screen and a housing (which was on special) for it from element14.

http://au.element14.com/raspberry-pi/raspberrypi-display/raspberry-pi-7inch-touchscreen/dp/2473872

http://au.element14.com/multicomp/cbrpp-ts-blk-wht/raspberry-pi-touchscreen-enclosure/dp/249469102

As usual, there can be a delay between purchase and actually assembly or use, due to other commitments. Anyway, a couple of nights ago, I decided to assemble the Raspberry Pi with the touchscreen. The touchscreen was pre-assembled, so all that I had to do was to attach the screen cable to the Raspberry Pi 3, then connect the four wires to provide power and the data signals to the touchscreen controller board. By the way, the instructions did not say that the SDA and SCL signals had to be connected and showed only connecting the ground and +5V pins.

I also needed to download the latest Raspbian operating system, and copy the image to a micro-SD card which I did the next day. Then finally plugging in the card, and fastening the Raspberry Pi down with four tiny screens. Next was placing all this in the housing. All went together and I connected up a suitable power supply and powered up.

Voila! Hmm, the display is upside down – ok, and the touchscreen wasn’t working. Checking out the FAQ on the appropriate sites indicates a fix for the display – to rotate by 180 degrees in the /boot/config.txt then a check to see if the touchscreen hardware was seen by the OS.  Yes, the drivers are active so what is going on? I decided that it was time to open it up and check the touchscreen cable.

To my surprise the cable was disconnected and sticking up at a right angle – then the penny dropped. Putting the case on, must have disconnected the cable, which was connected, but now is not.

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This is the touchscreen cable, the one that is attached to that black square chip – the cable is a little bent at the edge which meant that something was pressing on it. Turning the back of the case around showed me the problem.

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The cutout for the touchscreen cable has a sharp edge, which was pressing down on the edge of the touchscreen assembly with the chip on it, and since the thinner cable is not that long, pushing down on it would pull that thin cable out. Which is what must have happened. I measured the distance from the edge of the case to that touchscreen assembly, then marked on the case where I needed to remove that sharp edge. I got out my trusty file which happened to be almost the right width at the area I needed to file out, and proceeded to remove some plastic material making that marked area more rounded which would reduce the pressure on that assembly.

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Here is the final result. After careful reassembly and checking of the cable which was can just see through slots in the casing for the HDMI socket, I can confirm that the touchscreen cable is still attached.

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After powering up, I now have touch!