Author Topic: EEVblog #682 - Ness D16X Alarm Panel Repair  (Read 22125 times)

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Offline EEVblog

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EEVblog #682 - Ness D16X Alarm Panel Repair
« on: November 10, 2014, 11:35:59 am »
Part teardown, part repair, Dave looks at an Australian designed and manufactured Ness D16X alarm panel that has failed.
What's that smell?
Can it be fixed?
How do you repair solder mask on a PCB?, or add solder mask to your own home etched PCB's?
And another look at PCB spark gaps.

Datasheets:
Fairchild F8
http://en.wikipedia.org/wiki/Fairchild_F8
Holtek DTMF Receiver
http://www.holtek.com/english/docum/comm/9170.htm
Maxcap Capacitors:
http://www.maxcap.com.my/guideline.html
Epcos MOVs
http://www.epcos.com/inf/70/db/var_11/SIOV_Leaded_StandarD.pdf

 

Offline moemoe

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #1 on: November 10, 2014, 11:51:17 am »
Here is your Temp Rating: 85°C
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Offline EEVblog

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #2 on: November 10, 2014, 12:42:09 pm »
Here is your Temp Rating: 85°C

Ah, missed that on the camcorder monitor.
 

Offline mux

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #3 on: November 10, 2014, 12:54:30 pm »
Why did you need to repair this one? Where was it from? Who used it?
 

Offline skyline_stu

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #4 on: November 10, 2014, 12:56:53 pm »
I've used that same solder mask-it really needs to be a thin layer as you've suggested.

I think the micro's a Fujitsu H8-538 rather than a Fairchild device.. 

And on the phone line it's more likely a gas discharge arrestor. 
 

Offline German_EE

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #5 on: November 10, 2014, 01:36:22 pm »
Cut traces to isolate the damaged area and then build a small daughter board to hold everything from the input MOVs to the bridge rectifier. The hole in the PCB can be repaired with epoxy to prevent any more carbonized PCB escaping. I suspect that the single trace from the AC input is to monitor the mains supply, drive a 'mains fail' LED and switch over to battery power.
Should you find yourself in a chronically leaking boat, energy devoted to changing vessels is likely to be more productive than energy devoted to patching leaks.

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Offline free_electron

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #6 on: November 10, 2014, 01:40:10 pm »
Thats not a fair hild cpu but a Fujitsu ...
Professional Electron Wrangler.
Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 

Online Fungus

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #7 on: November 10, 2014, 03:34:30 pm »
Dremel out the middle bit. Couple of wires from the PTCs to the rectifier...job done!

 :box:
 

Offline SeanB

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #8 on: November 10, 2014, 04:14:32 pm »
Lost mains neutral in the supply system, and was exposed to 300VAC or more as it was the low current phase. Transformed to around 25V and this cooked the Transorb that was across the 17VAC rail.

The 7805 is the battery charge circuit, used with the ground lifted 9V1 by a pair of resistors to charge the battery with 13.8V, relying on the 7805 current limiting and overheat protection to protect the battery. The junction of the resistors to the 7805 ground pin is connected to the collector of a transistor, which is turned on every 15 minutes to turn the charger circuit off via the reverse blocking diode, so the MCU can read the battery voltage using a voltage divider on the board connected to an input of a multiplexer feeding the internal ADC. This is used to detect a failing battery so it will show a failure on the panel, and not fail silently with power off.

The keyboard link allows you to connect both multiple keypads and input extenders, so that you can have more than 16 inputs ( up to 48/64 inputs most likely with 2 extra expanders) on the same control panel. Lots you can do as well, like partition it. or you have certain inputs connected to fire alarms which operate 24 hours, and cannot be bypassed, or you can use it as a UL listed fire alarm.
 

Offline djQUAN

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #9 on: November 10, 2014, 04:26:53 pm »
Hi Dave,

Was thinking of sending you an email again but decided to join the forum instead, so here's my first post here. Please be nice to me ;)

I just saw your vid on the repair and would like to comment on a few things :)

As per some comments, the uC is a Fujitsu brand. It has a different "F" than fairchild. A google image search confirmed this :)

The part is an MB89F538 (http://www.alldatasheet.com/datasheet-pdf/pdf/153408/FUJITSU/MB89F538-201PV.html) 8bit uC.

Also, the part that has burned is most probably a ceramic capacitor for EMC/EMI. You have the two caps from each line to ground and then a third across the AC input.

In my previous work, for fire hazard reasons, we use two ceramic capacitors in series to prevent a direct short across the supply line causing a fire. With two in series, if one fails, the other will work fine no problem in the application.

What I think happened here could be that the cap experienced a voltage spike across the lines or that it is cracked in the first place after thermal cycling or board flexing causing an internal short which resulted to a direct short on the AC input line then causing the cap to burst into flames. (Yes, I have caused the same type of flame on a project when I subjected an axial MLCC with voltage spikes.)

Also, with regards to the MOV not being populated in the daughter board, we used to design everything into the PCB and populate everything in the initial design. After testing, we remove parts to save cost and check the performance if it still meets the requirements. If it still does, then we leave the part off in the next revisions up to the mass production stage.

-Raymond
 

Offline stitch

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #10 on: November 10, 2014, 04:41:10 pm »
The lettering on the PCB suggests that the designers intended the alarm to be oriented opposite of what Dave thinks it should have been.  If so, then the black residue isn't airborne soot at all, but rather downward flowing melt from maybe the case of the failed device.  Maybe in such an orientation, the heat stovepiped up the heat sink, produced that "bit of charring on the cap", and overheated the device that failed.
 

Offline SeanB

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #11 on: November 10, 2014, 06:21:13 pm »
Every alarm panel I have seen has the wiring at the bottom, with the board mounted right at the top of the case so you can fit the 12V 7.2Ah battery in the bottom, with all the wiring going to the cable exit in a mass of spaghetti with all colours. No other way, as you really want that battery at the bottom so when it does pop the gunk runs down and not across the board.
 

Offline Switching Power

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #12 on: November 10, 2014, 06:24:44 pm »
Maybe i have it wrong but when the input voltage gets above 70V RMS the two MOVs to ground are basically in series and would absorb any spikes above 70V.
 

Offline gardner

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #13 on: November 10, 2014, 06:30:52 pm »
How many layers in that board?  Is there a short in the internal layers?
You never showed us the back of that section.  What's it look like?

EDIT -- there is a quick look at the back at 03:00 or so, and a frame or two without Dave's hand in the way.

I was trying to see what J4 is about -- it looks like connecting the system ground to mains earth or leaving it isolated -- as here.
« Last Edit: November 10, 2014, 07:12:48 pm by gardner »
--- Gardner
 

Offline SeanB

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #14 on: November 10, 2014, 06:49:22 pm »
Maybe i have it wrong but when the input voltage gets above 70V RMS the two MOVs to ground are basically in series and would absorb any spikes above 70V.

True, but I would bet that MOV across the rails is going to be a 25VAC part, as the main capacitor is a 30V part, so it will definitely blow apart at 70VAC input. 25VAC part will start to clamp hard at around 30VAC, and this will give around 40VDC across the capacitor. Not optimal for long life, but most capacitors will withstand a 30% overvoltage for a few minutes ( solid tantalum being the exception, along with OSCON as well) without going bang. You often see a capacitor with a rating of say 35VDC with a surge voltage of 42V permissible. Most might withstand a 50% overvoltage for 10 minutes ( way longer than the time it should take the mains fuse to fail from the moderate overcurrent from the transient suppressor) with no ill effect, and possibly a few will show visible signs of bulging, or a blown safety vent.

The MOV devices to ground are there for lightning protection, along with the dual gas discharge tube on the telephone line side. Very common for high voltages to be induced onto phone lines and onto power lines, and to couple through the house wiring. The MOV's and GDT units are there to clamp this to a safe level, and couple the overvoltage to ground ( the installation also recommends a short high current lead to a grounded metal structure in a building, or to a dedicated ground rod outside or a copper or steel water pipe, to reduce impedance of this earth lead) safely. The spark gaps handle the internal iring spikes, note that the resistors used there on the inputs are not low voltage SMD devices but MELF packages that have a higher voltage rating and better surge capability.

As the alarm will have to be directly on the incoming phone line ( it has to be the first device so the relay can pull in to disconnect the inside wiring from the line to seize it under any circumstance) it will be exposed to all incoming spikes.
 

Offline sunnyhighway

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #15 on: November 10, 2014, 07:26:32 pm »
How many layers in that board?  Is there a short in the internal layers?
You never showed us the back of that section.  What's it look like?

EDIT -- there is a quick look at the back at 03:00 or so, and a frame or two without Dave's hand in the way.

I was trying to see what J4 is about -- it looks like connecting the system ground to mains earth or leaving it isolated -- as here.

Full bottom vieuw:
Close-up:
 

Offline electronic_eel

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #16 on: November 10, 2014, 07:38:45 pm »
Also, the part that has burned is most probably a ceramic capacitor for EMC/EMI. You have the two caps from each line to ground and then a third across the AC input.
That would be my guess too.

I have seen several MLCCs that went from ok to explosion or big flame after a year or two of use. I guess they crack through thermal stress, flexing of the board or improper solder profile during production.

The crack is not a dead short but low ohmic, so the power supply doesn't shut off but continues to deliver power, heating up the cap more and more till the flames come out.

The solution is either a very strict and tight current limit (e.g. an electronic fuse) or using two caps in series as Raymond suggested.
 

Online Yansi

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #17 on: November 10, 2014, 07:45:28 pm »
Have not seen the whole video yet (still watching), but Dave, you sure the two blue things are MOVs?  In the silk there is Y10, Y11.. common way to mark Y series safety capacitors (Y1 or Y2 - 2 to 4 kV rated, I don't rember the exact value).  Or have you read and decoded the part number?

//EDIT: Meh, really MOVs !  O0

But hey, thank you for some good video, about electronics, not that awful solar stuff. I look forwar for the next video!
« Last Edit: November 10, 2014, 08:37:01 pm by Yansi »
 

Offline Dave Turner

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #18 on: November 10, 2014, 08:15:30 pm »
Surely in practice this wouldn't be economical to repair.

However if it must be repaired and given the depth of burn damage I'd grind out all the damaged substrate including the tracks.
Then I'd use a compatible filler to reinforce the remaining board to the same thickness as there is a mounting hole at the corner. Then I'd create a small board to bond over the repaired substrate to mount the missing components and link to the existing connections.

How would you solve the problem if the unit MUST be repaired?
 

Online PA0PBZ

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #19 on: November 10, 2014, 08:36:03 pm »
So if you mix charred pcb with liquid soldermask it turns low R  >:D
Keyboard error: Press F1 to continue.
 

Offline moemoe

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #20 on: November 10, 2014, 09:16:16 pm »
Surely in practice this wouldn't be economical to repair.

Not only this, here (germany) it would surely loose it's VdS approval and therefore your insurance could refuse to pay.
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Offline Vito_R

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #21 on: November 10, 2014, 10:09:51 pm »
Ness is calling those small light bulbs "Current Limiting Globes" actually a cheap way they decided to go to regulate the battery charge current instead of designing a separate circuit.  The installation manual describes how it works:

Current Limiting Globes
The current limiting globes serve to regulate battery charging current.
When the battery is fully charged the globes will not glow. The
globes will glow slightly when recharging the battery after a short
power outage. If the globes glow very brightly the battery is drawing
excessive current and may be faulty, or the battery is connected in
reverse.
Do the job right the first time.  Quality over quantity will save you in the long run.
 

Offline ludzinc

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #22 on: November 10, 2014, 11:44:54 pm »
Lost mains neutral in the supply system, and was exposed to 300VAC or more as it was the low current phase. Transformed to around 25V and this cooked the Transorb that was across the 17VAC rail.

The 7805 is the battery charge circuit, used with the ground lifted 9V1 by a pair of resistors to charge the battery with 13.8V, relying on the 7805 current limiting and overheat protection to protect the battery. The junction of the resistors to the 7805 ground pin is connected to the collector of a transistor, which is turned on every 15 minutes to turn the charger circuit off via the reverse blocking diode, so the MCU can read the battery voltage using a voltage divider on the board connected to an input of a multiplexer feeding the internal ADC. This is used to detect a failing battery so it will show a failure on the panel, and not fail silently with power off.

The keyboard link allows you to connect both multiple keypads and input extenders, so that you can have more than 16 inputs ( up to 48/64 inputs most likely with 2 extra expanders) on the same control panel. Lots you can do as well, like partition it. or you have certain inputs connected to fire alarms which operate 24 hours, and cannot be bypassed, or you can use it as a UL listed fire alarm.

Hi SeanB

I always wondered how alarm panels did this - my panel at home is currently (intermittently) bitching about it's battery failing.  Time to swap it out.

But, you know, effort....
 

Offline EEVblog

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #23 on: November 11, 2014, 12:19:11 am »
Surely in practice this wouldn't be economical to repair.

From a business point of view, no. From a personal point of view, it's $200 for a replacement board.

Quote
However if it must be repaired and given the depth of burn damage I'd grind out all the damaged substrate including the tracks.
Then I'd use a compatible filler to reinforce the remaining board to the same thickness as there is a mounting hole at the corner. Then I'd create a small board to bond over the repaired substrate to mount the missing components and link to the existing connections.
How would you solve the problem if the unit MUST be repaired?

A slot as I said should be enough for bodge fix.
But yeah, an entire replacement board, or dug out and refilled with epoxy etc are more professional methods.
Any way you do it it's still a bodge though.
 

Offline EEVblog

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Re: EEVblog #682 - Ness D16X Alarm Panel Repair
« Reply #24 on: November 11, 2014, 02:38:23 am »
Thanks for a viewer submitted photo, I can confirm it is an MLCC used.
Clearly it has failed short circuit and heated up enough to catch on fire!  :o
I think this is potentially serious issue, and I have contacted Ness about it.
 


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