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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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.

Repair.IT – Asus Taichi 21 Notebook

This follows on from my data recovery of the D: drive of the Asus Taichi 21 notebook.  Actually, it wasn’t really so much data recovery as just copying files and folders from the SSD drive once I had it mounted, but this is about the repair of the notebook.  After I returned the notebook and the data, I was told that the owner would order a replacement motherboard and let me know when it came in so I could then fix the notebook.

In due course (a week and a half later), the motherboard arrived from the US and I got the notebook back. By the way, I didn’t mention about opening the case – there are 10 little Torx screws to be removed and then the two plastic feet near the hinges can be removed to uncover two more Phillips screws.  Then I disconnected and removed the battery, and then removed the heatsink/fan assembly.

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Once the heatsink came off, I could see that the cpu was covered with excessive amounts of thermal interface material – actually only the top of the cpu that contacts the heatsink needs the thermal interface material.  Then it was a matter of disconnecting and removing the wireless card, and the other connectors – then put in the replacement motherboard and reconnect everything.  For the heatsink, I used Arctic Silver thermal material to cover the top of the cpu as a thin film, then put the heatsink on top, jiggled it around a little, then screwed it on firmly.  The last thing was to install and connect the battery.

While powering on, I did notice that occasionally the screen would flicker but it stayed on most of the time, and when I closed the lid, the back screen came on as expected, so that was that – or was it?

The notebook went back to its owner the next day, and all was well – there was the occasion that the screen did not light up but after updating drivers, all appeared to be well.  At least until the owner tried to connect a couple of external monitors and somehow there was no display anymore.

I got the notebook back and I thought it would be strange if the motherboard was faulty again – but it is possible since they might only test it for a short time.  After some examination and reconnecting of the two screen cables, I found that one of the the connectors might have been a little dodgy, so I had to unplug it, then plug it in, unplug it and do this a few times – each time ensuring that it was lined up and would click back in securely.  This seemed to fix it and was able to get a working screen consistently and told the owner what I had done in case it happened again.

That was a couple of weeks ago and nothing has been heard of it since, which I guess is good news.

Repair.IT – Wise 2086 Professional Electronic Tension Head

Occasionally, in the electronic repair world – we may be unable to obtain replacement parts. In a situation like this, we then have to resort to replacing the module that has failed, either with modules from the manufacturer or modules that have a similar function.

This is about my Wise 2086 Professional Electronic Tension Head – which is mounted on my Spinfire Flame Stringing Machine. The tension head allows the string to be gripped, then pulled linearly until the required tension is reached – then, if constant pull is enabled, it will continue to keep that tension. A couple of weeks ago, I noticed that one of the segments on the second LED display didn’t light up. For those who know about 7 segment LED displays, it was the B segment. Sometimes like today, on powerup – it will be working.

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Wise 2086 Tension Head – display working

But then later on, the B segment will stop.

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Wise 2086 Tension Head – display not working properly

A couple of weeks ago, I emailed an enquiry to the supplier in Melbourne, Tennis Warehouse – from where I purchased this stringing machine about three years ago. I asked about any problems if I open up the tension head and mentioned the display problem. I had heard on the internet that occasionally, opening up the tension head would give an error on next powerup, that would require some procedure to be followed. I received a quick response that this will not happen, and that the screws are different lengths – something to watch out for when I open the case. Also that the display board is available for $45.

Just a week ago, on Friday, once I had finished stringing a few racquets – I opened up the case, then had to remove the main carriage to get to the display board. I removed the board and checked the part number of the LED display. It was a HS-3101AS – which is a 0.3 inch display but in a larger housing with 10 pins. I checked my usual supplier – element14, to no avail – this part didn’t appear to be available and I was unable to find an equivalent. A search on the internet also gave me a possible equivalent – HS-3101AX, but this also didn’t help.

I could find other similar size displays but when I check the pin connections, those are in two columns of five pins, 5 mm between columns, but mine are 7.62mm between columns. I could find it on alibaba, except that they only indicate it as being an integrated circuit will no actual photograph – so I was hesitant at ordering something, sight unseen. I decided then, to bite the bullet and order a replacement display board. I had to email a photo of the display board so that they could confirm the correct replacement. Then on Thursday – my replacement board arrived.

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Display board for Wise 2086

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Display board for Wise 2086

The top on is the original, version 3.1 and the replacement is at the bottom – version 3.3. Some slight differences – the main thing being that the speaker was moved, making it much easier to install the board.

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Wise 2086 Tension Head

Here is a photo of the board installed – at the top. Previously the speaker would get in the way of my fingers when trying to remove and install the small brass nut.

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Wise 2086 Tension Head

Then a photo with the carriage mounted back on.

Next thing to do is to work on one of the base clamps on the stringing machine – which had been causing problems that it would unlock, when I didn’t want it to. Tennis Warehouse sent me a replacement base clamp at the same time as the display board which was very good of them.

The motto of the story is that you cannot always replace component parts – in fact, not many companies will do this, even for manufacturers – they usually replace the module. Sometimes, if the modules are valuable – they are returned to the factory for refurbishment – which usually means replacing the faulty components, but not always. The common factory refurbished cameras and whitegoods – are usually just repaired with replacement modules – often happens with goods that are dead on arrival, they go back – repaired by swapping modules, then comes back out as factory refurbished at a very good price and with warranty, generally.

Repair.IT – Sedco 24V / 12V Power Supply

Just over a week ago, I was asked if I repair power supplies – I said sure, so this Sedco 24V / 12V Power Supply was carried out to my car and placed in my boot. It certainly looked heavy, and when I got it home and opened the cover – I realized why.

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The insides of the Sedco power supply

There are two 12V batteries inside, obviously looking very much the worse for wear – the acid corrosion on the negative terminal of the right side battery contact is a sure sign of battery failure. Certainly when I measured both batteries, I was getting only 6V on the left one, and about 4V on the right.

Ok, the usual checks are the fuses – are they intact? Yes, they measured fine with my multimeter. The actual power supply is in the metal box at the top left – the one with the five multi-wire connectors . The left connector is the incoming mains power, next one is the battery connection, then the output voltage, and two with lots of wires going to leds, etc.

Next thing is to remove the power supply. This was a fairly standard switched mode power supply, however it has a couple of plug-in boards that connect to the main circuit board. The incoming mains is rectified and conditioned by the plug-in board on the left – I don’t actually have a photo of it, but it is where the mains connector is attached. The second plug-in board seems to be for the two multi-wire connectors, doing things like driving the leds on the front panel.

This little board did have three electrolytic capacitors that were bulging – we have mentioned this previously, that these have most likely failed. I didn’t have 1000uF 35V 105C capacitors in my stock, so had to arrange to get them. I got these in due course and replaced them together with a 100uF 35V capacitor that had also failed. I checked also the semiconductors – such as diodes, mosfet’s – but they all appeared to be intact. The fuses being intact also indicates no catastrophic failure.

The power supply was reassembled, and everything connected back together, then power was applied, and… nothing – no lights, no bang – basically nothing happened other than the switch clicking on. Ok, so the power supply is not starting up – what could be the problem?

Removed the power supply and started having a closer look at the main circuit board. A fairly standard layout – the startup circuit is the one to look at. I spied a small electrolytic in the startup circuit – when I measured the ESR, it was 8.4 which is very high. Unfortunately, the capacitor was hidden away with other large components near it so I could not read the value of the capacitor. A low value capacitor could potentially have a high ESR so being high is not necessarily a definite sign of failure. This capacitor is connected to a UC3845 SMPS controller – which is a fixed frequency current-mode PWM controller.

I did a bit of research on this controller and came across a little tit-bit of information, that if the Vcc capacitor was faulty, a UC3842 PWM controller likely cannot start. As this UC3842 is in the same family as the UC3845, I thought that this capacitor was likely to be faulty. I then desoldered the capacitor and found that it had a value of 100uF 35V. At this value, definitely the high ESR means that it had failed. I had one in my stock, so replaced the capacitor – then reassembled everything.

Finally, I connected up my power meter to the power supply then turned on, and… it powered up, at least the power light was lit – also the low battery light was on. I turned off and went to have something to eat. When I came back and powered up again, I could now see that the 24V and 12V lights also came on. I measured the power rails on the back of the power supply, 12.2V for the 12V rail, and around 25.2V for the 24V rail.

The 24V rail was fluctuating a little and certainly wasn’t 24V but higher. Why is this? Ok, it has to charge the batteries, of course, so needs to be higher than 24V – at 25.2V, the batteries could be connected almost indefinitely and should not show signs of overcharging (ideally). Of course, the batteries were not in good condition, so maybe replacing the batteries would give a more stable 24V rail. Anyway, it certainly looks like it is now repaired and working again – I can’t do more until the batteries are replaced.

[Note] This power supply is used in nursing homes and hospitals associated with medical care. The power supply will provide 24V and 12V normally – and if mains power fails, it will still deliver this via the internal batteries until such time as they go flat.