Repair.IT – Temporary fix of rusted letterbox post

While doing the lawn mowing yesterday, I noticed that as my mower brushed next to the letterbox – the letterbox shook. I then had a closer look and it was staying upright, but it could be pushed backwards with a little force. It was still attached at the back mainly, away from the street, but the steel post has most likely rusted almost through.

Once I brushed away the dirt and removed the grass that was covering the concrete block, I could see that there was a rusted hole in the post. The concrete pad used to be at the same level as the grass but the grass has grown up, and the dirt had migrated, causing the steel post to be covered with dirt and allowing moisture to attack it.

I decided to make a temporary repair – to remove the post, then insert a piece of timber that would fit inside the post and in the hole left in the concrete. First step was to remove the post – I was able to bend the post down and could see that the hole was also full of water.

I used a universal tool with a metal cutting blade, and cut the post off at the level of the concrete.

Next step is to cut off as much of the rusted section as I could, and then to clean out and empty the hole or water and dirt. I was able to soak up much of the water with a small rag, then scraped around the bottom of the hole, then used a vacuum cleaner, to remove the dirt and debris.

I needed a section of timber that would be 35mm square. I didn’t have anything to hand that would suit but could join two thinner pieces together. I remembered that I had some small pieces of Blackbutt decking board leftover from building my deck. Blackbutt is an Australian hardwood and is suited to outdoor conditions but I would need to do something to protect it from moisture eventually.

I cut a piece of Blackbutt to 150mm in length, then cut a section of it to about 35mm thickness. As the decking board is 19mm in thickness, I glued two of these pieces together, then after it was dry, cut the side to be a total of 35mm thick. It had a firm fit on the steel post, so next thing to do was to try and hammer it into the hole. It wasn’t easy to do, and only managed to get it in partially, so that might have to do. I could see the concrete pad moving as I was hammering it in.

Then finally to put the post back on – I had taken the actual letterbox off the post, and was able to hammer it onto the Blackbutt section. It seemed to be very firm – and didn’t seem likely that I could easily take it off again. When I push on the post, I could see that the concrete pad was shifting.

Anyway, it seemed to do the job – although as I mentioned, it is a temporary fix. The best option, would be to buy a replacement post, then dig up the concrete, and install the new post in new concrete, but this time, make the concrete higher that the ground level and slope it so that water doesn’t stay at the bottom of the post. In any case, concrete is alkaline and would cause corrosion anyway of the steel post. Maybe I should think of another way to install the new post.

For now, it is quite serviceable, and definitely will not fall over when the postman next puts a few letters of parcel into the letterbox. To help the timber last, I should most likely fill the gaps and seal it maybe with a waterproof paint – let me see what I have sitting around. That’s it for today. I know that this won’t last long, but who knows – it could well last a year. That should give me plenty of time to arrange a replacement post.

Repair.IT – Repair of smoky Amtex HSC40-20 Switched Mode Power Supply

Just recently, the Segway Ninebot One S2 that I had repaired previously came back for me to look at – a battery problem again. I removed the covers and took the battery pack out. Sure enough, the battery pack had failed, so I opened the battery pack and was setting up to check and charge each lithium cell.

I have a modular Amtex HSC40-20 switched mode power supply that had 12V and 5V outputs. This power supply was housed in a plastic box with banana sockets on the front. I have used this power supply from time to time to power up and check IDE disk drives using the attached Molex cable. I decided that the 12V output would just be ideal to power the Swallow battery charger for charging the lithium cells.

Once everything was cabled up, I commenced charging the lithium cells. Cells #1 and #2 were fine, still with a full charge, but when I went to charge #3, I heard a slight pop/hissing sound – then looking around, I noticed a wisp of smoke coming from the power supply – so I hurried switched it off.

I disconnected the power supply and took it over to the screen door in order to open it up (in case of a lot of smoke). After removing two screws, the top cover was removed and this acrid smoke came out. The box was full of this smoke. I put the box outside on the deck to let the smoke dissipate. After a number of hours, I brought it back inside, but the smell was still there – so after a brief inspection, put the top cover back on for the time being.

This power supply was one of two that I had purchased many years ago – and the date code on the label shows 8432. Translating this date code using the legacy notation indicates that the power supply was manufactured in Week 32 of the year 1984. Not bad for a power supply that was 37 years old.

What had failed was a 0.1uF MP X2 capacitor right next to the bridge rectifier. This metallized paper capacitor is part of the EMI/RFI suppression filter that is meant to remove electromagnetic noise and interference from the incoming mains.

I got my other unused power supply out of storage to examine and to do some comparisons. It was easier to take photos of this one without the attached wiring.

A photo of my unused power supply (Serial number 1839).

I could see that there were very fine cracks in the same capacitor and in two other MP X2 capacitors which was part of the same filter.

A closer look showing the position of the MP X2 capacitors in the other power supply.

On further examination of the failed power supply, I found two capacitors on the DC outputs that I appear to have replaced previously. I must have been in a hurry back then, as I had replaced them with axial capacitors instead of radial capacitors. I should replace those as well, while I do this repair. I forgot to take a photo of the actual failed power supply but here are the MP X2 capacitors after removal.

The failed capacitor is a 0.1uF 250VAC MP X2 capacitor. It is made from metallized paper folded and encapsulated in plastic. The age cracks in the plastic must have allowed moisture to enter via the humidity in the air, and this must have degraded the paper insulation, causing the capacitor to fail. The X2 rating means that it is mains rated and would fail in a shorted configuration which would normally blow the power supply fuse. I was able to switch it off before it shorted completely.

On Thursday, I ordered the replacement parts from the local Jaycar in Rydalmere, and picked them up as they had all of the parts in stock. The replacements are all polypropylene so should never need replacement due to age. The repair was straight forward, first installing the DC output capacitors, then installing the replacement X2 capacitors which were yellow in colour now, instead of grey.

Note the serial number 1847!

After this repair, I switched on this power supply, and was able to measure the right output voltages from the terminals – and no more smoke, although the odour is still present. I then proceeded to replace the MP X2 capacitors in my other power supply and then stored that one away in its foam wrapping.

This should remind me to be wary of old power supplies that had been sitting around unused for long periods of time. Don’t leave them running unattended or inspect these parts before using the power supply, if possible. Anyway, another repair (or two) completed.