Another follow up to Marmitek/Haibrain SC9000 PSU (PS90U) failure

Here we go again, I've had another SC9000 power supply failure. For those that have been following my blog before you'll know I use an SC9000 X10 alarm system, and last year the power supply PS90U failed on it.
The power supply fails in an odd way, it still provides power to the alarm system, so everything appears fine, however when it fails it stops sending or receiving X10 commands, which is critical as the X10 commands trigger the siren/sounders and show the alarm as triggered.
I noticed that the timed lights weren't coming on and off when they are supposed to. These are controlled by the timer light functions on the SC9000, and so this made me suspect it yet again.

Sure enough, checking the PSU out, I found it wasn't sending/receiving the X10 commands through it. So time to check what's wrong.
Firstly. This is the 2nd unit I've had to purchase. The first failed in the same way, and now this one, less than one year since I bought it (Purchased 04/06/2016, failed 17/04/2016). So these units really aren't reliable. Originally I thought this was due to heat and so put heat vents in this PSU last year, however it looks like this hasn't helped.

Opening the unit up, again it has the stench of burnt electronics. They are comprised of a large transformer, some mains filter circuitry (and DC step-down) and then the X10 circuitry.

The first photo shows the transformer and the mains side of the circuit. You can see to the lower part of the board the discolouration of the circuit board, which is where the transformer sits, so the transformer obviously runs hot.

After stripping away some plastic covers/heatshrink, I revealed a glass fuse (I was expecting a resistor that was being 'used' as a resistor). Other components on there such as the capacitors, etc, looked OK, they weren't bulging and putting the meter on them showed the 'correct' resistance rising up to infinity, so they appeared OK.

The larger yellow component (visible in the photo) MPX275-X2 is a surge AC capacitor, small blue circle (to the right of the first photo) 

Various transistors are there 2SC667 which is an NPN transistor used for switching high current from a low current source (So most likely output from the chips on board)

Anyway, after various tests, none of the components appeared to have failed, which was odd. So I then started probing parts of the board for continuity, thinking heat may have fractured a trace. I wasn't getting much continuity from the mains leads (red and black in the photo) to anywhere, and then I tested the fuse. It was open circuit, so it had blown. It's a small 250mA 250v fuse, so a very small value.

Following the wiring of it, I realised that the mains wires (red and black) come in, directly connect to the two brown wires (to power the transformer) but then go through a fuse, choke, etc, and into the circuitry. So the transformer IS NOT protected by the fuse, but the small electronics ARE! How strange. So what was happening was the transformer was still working and stepping down/providing the low voltage to power the SC9000 alarm, but the fuse had blown and so the X10 circuitry in the PSU weren't getting any power. Hence the failure mode of these units, when they fail I suspect that is always the weak point, but rather than stop the whole thing working (A much better failure mode to me, in that you'll know it's failed. Rather than waiting until you need the alarm, and it not sounding!).

I did a small test, I bridged the fuse with a replacement, and hey presto, it started working. Now why the fuse failed I'm unsure, it was a very small current (250mA) which makes me think even a small electrical surge would cause it (The fuse was directly on the mains input, not after the smoothing capacitors, etc) so that's what I'm thinking. Especially as I've found that this does seem vulnerable to electrical surges.

So a quick replacement fuse and it's working again. But for how long?!

Follow up to Marmitek/Haibrain SC9000 PSU failure

This is a bit of a follow up to my previous post on the Haibrain SC9000 X10 alarm unit that I use at home. I decided to bite the bullet and purchase a replacement power supply (£15 so not cheap, but then again not too pricey) and it arrived a few days later. I've finally got round to fitting it and as I did made a few observations and notes for the future.

I took quite a few photos which are all in this post, so apologies for it being graphically heavy.

Firstly, the new unit arrived, and unboxing showed it to be identical to the original, no change to voltage, current, etc. So first thing I did was connected it up as a test and checked, yep the alarm would now sound and all the X10 commands started to flow, so it appears this IS a faulty power supply that causes the alarm sounder not to trigger and the X10 commands to fail. At least I'd now determined the root cause of the fault, it wasn't the overall alarm unit.
Next, I wanted to try and see WHY the original failed and if possible make the new one last longer. One thing I'd always noted was that it ran hot, as most step-down transformers give off heat this isn't unusual, but they generally have vents or at least some way of expelling the heat. This one doesn't, the power supply is a sealed black brick, no vents or anything and when I say it ran hot, you wouldn't want to hold it in the palm of your hand long, it's that sort of heat. So my thinking is I give it some vents before I put the new one into service to help loose the heat, my thinking is most electronics prefer to run cool than hot and it might stop the failure occurring again.
This meant my favourite (ha ha) thing of all time, take something brand new that I've just paid for, take it apart and modify it! But luckily these PSUs have 4 clear screws and a simple case, so taking it apart isn't a challenge. Once opened up, split the two halves of the case carefully as one circuit board stays in one side, the other in the base as you can see from this photo with the case carefully separated:

The right is the "base" which has the main transformer and a circuit board that covers the base, along with at the top right the 2-pin mains in socket.

The left "top" holds a much smaller IC-containing board and the output wire that feeds to the alarm (4-wire). The small circuit board has a single screw in it (just visible on photo, bottom left) so take that out and the top casing comes completely clear. This was ideal, my thinking was to make air vents right along where that bulky transformer sat as that's where the heat was generated, and it was VERY snug alongside other electronics, so a good bet.

I set about the case with my dremel, and here I show my failure as a practical/mechanical/precision person, the air holes are horrible, not neat, but I sanded them down so no rough edges and I think they'll do the job.

 

As you can see they aren't neat, but should allow a bit of heat to escape. Putting it all back together and it looks like the vents are in the right place, right over the transformer.

Now since I fitted the front of the SC9000 to a wall, and then fitted the cable into the gap between the plaster and wall (inside the wall), the next problem was re-feeding the wire to the right place. So I decided not to, and to simply cut the cables and join them back up using a connector block. That way I didn't have to re-trace the cabling in the wall and make life a lot easier!

As you can see, I was feeling quite neat today and even used a connector block (instead of twisting the wires together and taping them together). I then wrapped the block in tape so it was secure and no potential for shorts or anything getting in there.

Putting it all back together, power on and it all worked fine!
(Note for later, when the batteries are low, the green battery light stays on! I thought the power supply had blown somewhere in the process as the green light stayed on. Seems the green light not only shows it's running on batteries, but also that the batteries are low!)

Next, I decided to properly pull apart the old supply, as I'd like to find what failed and possibly fix it, so in future I have a way of repairing these things with just a few parts.
Below are a load of photos of the teardown, I've not yet had time to investigate all the parts but will do very shortly and probably try a trial and error of replacing parts until I discover the failed unit. However as you'll see there are quite a few scorch marks on components, so I'll be starting work there, which is also where I believe the mains part of the circuit resides, hence this bit will be more susceptible to mains spikes, etc, (which is what Marmitek/Haibrain state as the issue when the PSU fails, it's a mains spike)

The main split board from above

The smaller IC board

The top corner of the main board, no obvious damage here.

 After removing the transformer, some scorching of the main board was clear, I'm now suspecting this is where the issue is.

 Underneath shows more heat damage.

 Closer view of the high voltage components that sit almost exactly underneath the transformer.

After inspection I suspect looking at these components closely, however they are only a couple of resistors, so I'm not hopeful that it would be something as simple as these failing!

Marmitek/Haibrain SC9000 X10 alarm system

* Updated 02/06/2015 (See end of post)

When we moved into our new house a year ago, I decided to go for an alarm system that I'd be able to integrate with, and use with my home automation that I keep trying to build upon and improve. I already had various X10 home modules (lights and appliances) and whilst some of these modules are poor quality and fail quickly, it is a good system that has worked for me. I have the CM11a conneted via serial to my server in the house so it can monitor all X10 codes and also send them for turning outside lights on, living room lights, etc.

So I looked into it and went with the SC9000 home alarm system from Marmitek (Who are now called Haibrain) as it was a fully integrated X10 alarm system, it could send and receive X10 signals over the home powerline and also used wireless door and motion sensors in the house for triggers.

The above is a stock image, but it's similar to what I got, I added more sensors and an external bell box. I fitted the unit into the hallway in the house, cut a hole in the wall and fed it to be supplied by a mains socket. This was the first challenge. The PSU looks like this:

Which is kinda tricky to install for an alarm system! You want things like that hidden (So burglar doesn't unplug the alarm!) and that huge power brick and hard-wired plug was a pain. I also did a bit more reading and found that power brick isn't just a step-down transformer. Since it has to send and receive X10 signals it actually has a lot of the X10 circuitry built into it.
So my plan was, install the front facing alarm unit somewhere public, then run cables away somewhere hidden. The house lent itself to this so I got it fitted and sorted. The alarm had backup batteries internally, so it was protected even if the power was cut.
Registering the wireless motion sensors and door sensors was easy and the remotes to arm and disarm the unit, etc.
The unit wasn't as flexible as I'd hoped, you couldn't specify which zones you wanted for "home set" and "away set". I.e. when "home set" it will only activate the door sensors, no motion sensors. And "away set" activates all sensors, no option to exclude. This was a bit annoying, but the unit didn't have much flexibility in it's programming.

Anyway, I lived with all of that, and now almost a year later the unit has stopped working in quite a critical way. It won't alarm! It sets, it will do the exit timer chimes, and notify when people open doors, but critically if it's triggered it would sound the main alarm sounder. It is also not sending or receiving the X10 signals.

Again, reading up, it appears the PSU on these units is particularly sensitive and will 'blow' in a partial way quite easily. My PSU has always run pretty hot, this seems common with X10 stuff, and it looks like after around a year it's given up. It still supplies the correct voltage, etc, so the alarm is on but critically it won't send or receive the X10 commands (So can't send the 'ALARM ARMED', 'disarmed', etc) and it also won't trigger it's main alarm siren.

I've contacted Marmitek in the hope of finding a solution, as I am also not 100% sure this is a faulty PSU, or some other fault that has been developed. Either way I want an answer as surely it has a longer life than a year on it. If it does indeed turn out to be the problem, I think an alternative is needed as I'm not going to keep replacing these every year for an alarm system, seems excessive that, as electronics should be more capable than that.

* Update 02/06/2015

I've had a reply back from a UK reseller of the Marmitek equipment regarding this issue, and they do indeed state that it was likely a brownout or power spike caused the PSU X10 electronics to fail causing the situation I've got. They've recommended their replacement power supply at £13. I've contacted them back asking if anything can be done to protect the supply, as my understanding is I could buy a new one, plug it in and if I get another surge next week that one will blow. And putting it behind a surge protection multiway I suspect would stop the X10 signals. I'll post back if/when I get a reply, but in the meantime it doesn't look a very good solution to me.