Regrease.IT – Losmandy GM-8 Equatorial Mount

The other day – actually around the middle of July 2018 I was talking to friends about Mars being visible.  Then there was shortly going to be a lunar eclipse.  In preparation of viewing the much anticipated lunar eclipse that was going to be the longest duration event for a long time, I dusted off my telescopes to see which one would be suitable to use for the viewing.

I went through some of my telescopes, one of them was a computerized Meade LXD-55 with a 6-inch Schmidt-Newtonian, but the view of Saturn was a bit small, so eventually settled on the big monster.  Some years ago, before I started travelling, I had purchased a Losmandy GM-8 equatorial mount, together with a Meade 10-inch Schmidt Cassegrain optical tube assembly.  Due to my travelling, and subsequent house move, this combination had very little use and was mostly in storage.  The mount had been sitting in a corner for quite some time, and the optical tube assembly was inside its original box.  I thought it would be a good time to let it see the light of day (or night) again.

A few days earlier, I had set up a measuring stick so that I could mark the Sun’s shadow at solar noon, which happened to be at 12:01 PM on those days.  Knowing which direction the Sun’s shadow pointed to, at solar noon, meant that I could accurately know the direction to the South Celestial Pole (SCP).

One leg of the Losmandy tripod was set in the direction of the SCP, then the mount was installed on top, so that the Right Ascension axis would point towards the SCP.  The idea of this is that the RA axis, being parallel to the direction of the SCP would be in line with the rotation of the Earth.  The motors driving the RA axis would counteract the rotation of the Earth so that the stars, planets, moon etc would appear to be stationary.

Of course the slightest misalignment would mean that some adjustment would still be needed, but having it close would mean that it would be small adjustments.  I am digressing I think – just setting the scene to what I had in mind.

So during a nights viewing of the Moon, Mars and of course Saturn – I noticed that when slewing the telescope in the RA direction, the view would move then when I stopped slewing, the view would come back a bit, which in some ways is like backlash in gears – but this was enormous.  I had noticed that the RA axis was a bit stiff, since I usually balance the telescope – and had a lot of trouble doing so, but since it was still usable, I ignored it at the time.

As it turns out, we were very clouded out on that Saturday, so there was little viewing of the lunar eclipse.  In the following days when the clouds cleared up, there was some viewing, and then the rain came.  Of course, I didn’t leave the optical tube outside, but did leave the mount there, covered with a plastic bag.  During a violent wind storm, I came home, and the bag had been blown off, never to be seen again.  I decided it was time to bring the mount inside.

When inside, I was then able to have a much closer look at the stiffness of the RA axis, in fact – it was so tight that I could feel some cogging, which meant to me, that the bearings had stopped working.  After some thought, I decided it was time to see about getting to the bearings.  On Google I found a number of people had seen this problem, especially when the mount was in storage for some time.  This mount is about 20 years old, spending much of its time in a corner as I had no permanent place for it to live, like an observatory.

I removed the Declination axis, which was bolted onto the RA axis with two bolts.  Then removing the various bits, left me with the RA axis tube sitting inside the RA assembly.  After careful consideration, I used my rubber mallet to knock the tube loose.  I had already loosed the main gear and worm drive, removing the motor – and as it turns out, I could have left those intact.  After some effort, the tube came out and I could see that the tube showed the signs of frozen bearings.

Then after moving the RA assembly to a horizontal position, here is a picture of the lower bearing.

And of course a shot of some of the bits that came off the mount.

I could feel that the needle bearings were not spinning, which is a bad sign.  After rubbing it, I sprayed the bearings with WD-40.  One of the bearings is not visible, being set inside the assembly.  The WD-40 can had a long nozzle which I used to get the liquid inside.  Using a cotton cloth, I could move my fingers around and around the bearings – and they seemed to move a bit.  Some of the old caked grease was starting to come off.

I got as much of the old grease off as I could, then sprayed more WD-40 and left it overnight.

The next day, I then used a cloth to clean the WD-40 out of the bearings and the bearings seemed to be working – with the needles spinning somewhat.  More spinning of the bearings and another application of WD-40 and it seemed to be clean enough – at least the rag I was using was not coming out with a brown coloured gunk, but was coming out clean.  More work with the rag, until it was coming out dry.

Leaving overnight again, for any further WD-40 to evaporate, then clean again with lint-free tissues, before regreasing the bearings.  Before regreasing the bearings, I tested them by inserting the RA tube, then rotation the tube, which went well.  I then used a white lithium grease that is in a spray can, typically available from most places like Bunnings, SuperCheap Auto, etc.

I sprayed the grease onto a piece of cardboard, then used my finger to scoop some grease and work it into the bearings.  After further applications and doing the upper bearing that was inside the RA assembly, I was satisfied that I had sufficient grease on the bearings.

Then it was time to reassemble the RA axis, effectively – install the main thrust bearing, then the main gear that has the RA setting circle mounted on it.  Install the worm drive, making sure that it meshes with the main gear, then mount the motor drive, and then worm drive cover, and finally insert the RA axis tube.  At the lower end of the axis, install another main thrust bearing, then the clutch knob spacer, the clutch knob spring washer, then the clutch knob and tighten it up.

Almost done, now – what am I missing.  Ah yes, the Declination assembly – this bolts on to the 2 holes in the RA axis tube.

Ok, finished – regreasing it.  Well, almost!  I still have to adjust the worm drive since there is still some play in it – I need to adjust the meshing of the worm drive with the main gear so that it is tight enough that it will rotate well but loose enough that it doesn’t bind or have any tight spots.  I adjusted it as best as I could, but I would have to revisit this again next time I use the mount.  All of this was done over several days and apparently, this regreasing may need to be done on a regular basis in the future, maybe every year or two.

I did mention that the RA axis tube is hollow, right?  That is so that the polar scope can be mounted into it, so that we could adjust the axis to point directly at the South Celestial Pole, which is located somewhere in Octans, but I am digressing again…

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Repair.IT – Highgate wall light with PIR motion detector

Here is something that was on my bench for repair. A Highgate OL7664BK outdoor wall light with PIR motion detector. It is a nice light made from black metal housing with glass pieces which had been installed at a sister’s place during a small renovation, and then failed to turn on, a few months later.

After making contact with the supplier, a replacement light was sent out. In due course, the light was then replaced, and I was given the faulty unit – perhaps I could Repair.IT and get it working again.

After opening the light housing where the sensor is located, I found that the sensor unit is a small black box with the PIR on the outside and three wires going into it. Brown, Blue and Red – guess what these would be? Fortunately, they also went to a terminal block which was marked. Brown and Blue are standard colours for Active and Neutral, but Red’s marking was an X – ok, meaning switch.

Sure enough X went to the Active of the light socket, with Neutral being the common for the light socket. Also I noted that there was also a ground wire terminating onto a stud on the metal housing – that is very good indeed. Now, the light is still usable if we wish to use it just as a standard light fitting, without the PIR sensor by just wiring the input wires to the active and neutral of the light socket.  However, I am interested in how to fix it.

The small black box was sealed, but nothing a rubber mallet couldn’t solve, so eventually the seal where it was either glued or plastic welded – came apart and I could get to the interior.

Inside was a small board that was connected to the separate PIR sensor board. Often the question I get asked, is how do we determine what the fault it.  Generally we will know something about the device, in this case – it is a switch that turns on or off the light.  The PIR sensor board does the sensing, so it must then use the small board to switch the light.

Usually this involves an optical isolator which is usually in a small 4-pin or 6-pin package.  This optical isolator, or opto isolator will then somehow connect to a switching device, which is usually a triac.  This small board contained a MOC3023 which is a known optocoupler with a triac driver output.  From this chip, it connected to a triac via a small limiting resistor.

I examined and determined that a Triac had failed. In additional the small limiting resistor of value 200 ohms had also gone open circuit.

Likely what had happened was that the Triac had failed, and the ensuring high voltage caused excess current to flow through the tiny resistor which then failed. Or it could have been the other way around, but the resistor is slightly discoloured which meant that it had gotten way too hot.  In this photo, the resistor is the one near the top left.  The marking shows 201 but the 0 is a bit marred.

The marking on the Triac was a BT136-600E. My local Element14 supplier had these in stock, for around $1.26 but then ordering this by itself  plus the resistor would incur a delivery fee much larger than the total.  Since this was a charity repair, I elected to buy these parts on eBay.  10x BT136-600E’s were $1.86 delivered, so this was a good deal.

The resistor was a 200ohm surface mount version in a 1206 package – I managed to find a good supplier that would give me 100 pieces for $1.34 delivered.  In the case of eBay, why buy 1 when you can get more for a similar price.  It leaves me with lots of spares for future repairs.

The BT136 was easy to remove, just using my desoldering station – it was a matter of minutes to desolder each pin and remove it from the board.  Similarly, but using a SMD tweezer soldering station, the resistor came off in a few seconds after heating.

Once the parts came in, which was a few weeks in most cases – I soldered the replacements into place.  Here I am showing the replacement resistor with a good 201 marking.

Here is a view of the top of the board, showing the bad triac on the board mounting.

In case you are wondering how small a 1206 resistor package is, it is 3.2mm long and 1.6mm wide, just don’t drop it on the carpet, since you may not find it again.

Oh, by the way, once assembled and wired up on the bench – it does work.  The light would light up when I walked near it.  Another successful Repair.IT

Reply.IT – Reply to comments

Hi, first of all, I would like to apologise for being slow at responding to replies.  So today, I got onto another computer, logged on to WordPress.com and went through the comments and replied to them.

I switched computers because my main desktop was getting old, and on the new computer, I was playing a number of online games.  I also built a number of new cryptocurrency mining PC’s of which I may document at a later time.

Also with internet issues, I found that I could not even approve comments and write new articles.  Anyway, I managed to get the WordPress app onto my Android phone and was able to approve the comments a couple of days ago.

Now I have replied to most of the comments and will endeavour to respond in a more timely fashion in the future. I also have some articles lined up which I will upload soon.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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%.

Here is my replacement capacitors wired together.

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.