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Author Topic: Another heating issue  (Read 1904 times)

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Jimbob

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Another heating issue
« on: 05 April 2018, 08:13:19 »

Its the turn of my warm air central heating to need mending  :'(

It was playing up bit time, investigation revealed this

full size below if you want better zoom
http://images.omegaowners.com/images/Jimbob/IMG_3655.JPG

Question is, is this repairable?  Clearly some components (at least the central varistor, and 1 resistor) are unidentifiable as theyve melted....but why?
Am I ok to just replace these?

Ive bought a new PCB as it seemed the best option to quickly get the system running again, and to also identify the bad components, as this isnt a common unit theres not a lot of info out there on it.  Ideally I'd like to repair this in case of 'next time'.  clearly no urgency to this now though.

Can put other photos on if needed.  Of old or new

Kevin Wood

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Re: Another heating issue
« Reply #1 on: 05 April 2018, 11:18:13 »

Doubtless it could be repaired. I'm guessing that thermistor is probably there to limit inrush current given its proximity to a bridge of 4 diodes. Maybe something has shorted upstream and cause it to lunch itself (failed capacitor, or one of the diodes?). What does the board actually do?

I would try to trace out that portion of the circuit to determine what it does before trying to figure out what has caused the failure.
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Marks DTM Calib

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Re: Another heating issue
« Reply #2 on: 05 April 2018, 12:16:58 »

Any pics of the complete circuit board?

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Jimbob

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Re: Another heating issue
« Reply #3 on: 05 April 2018, 12:23:09 »

Tracing is a bit beyond me

Got pics of the new board with me, but not the old, can take those later, depending which you wanted?


full size below if you want better zoom
http://images.omegaowners.com/images/Jimbob/IMG_3646.JPG

Jimbob

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Re: Another heating issue
« Reply #4 on: 05 April 2018, 12:26:40 »

The board is the Main ECU for the heating and hot water.
System uses a thermisterstat not a thermostat and adjusts heat output relative to ambient temp, so hot fast fans when its cold, warm slower ones if its warm.
Also does normal stored hot water
Also slowly reduces heat and air output once cycle over
Also has diags built in on display to show what stage of cycle all at.

Kevin Wood

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Re: Another heating issue
« Reply #5 on: 05 April 2018, 12:48:44 »

Ahh, OK, so I'm guessing the connection marked "circ.fan" goes to some motor that is speed controlled?
I think that corner of the board is a speed controller and it does look like the mains input goes to those rectifier diodes.
I see they've changed that thermistor for a different style on the new board. Telling, perhaps?

To glean much more I'd need to have the board in-hand but I'd be looking to understand what that bit of circuit does and check any components likely to have caused the failure, then replace the damaged bits and anything else that might have triggered the failure. It looks a simple enough device, though, so I'd say it's probably a simple fix, as long as the CPU isn't dead. Was it showing any error codes or signs of life, or just completely dead?
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Jimbob

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Re: Another heating issue
« Reply #6 on: 05 April 2018, 12:55:29 »

Cheers, board was working....of sorts.

We had full power heat only.
And when the system was off, we had full power cool fans / summer vent mode!

Only way to have it do nothing was off at the mains

Marks DTM Calib

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Re: Another heating issue
« Reply #7 on: 05 April 2018, 15:29:00 »

I would be wary of that power switcher, given the fan has been running flat out all the time it may well be short circuit.

At a guess the mains is being full wave rectified and then switched by a thyristor or mosfet (the device in the heat shrink), those discs look more like transient suppressors to me and are known to be crap, if they fail then the power device will see all sorts of nasties and may well fail short circuit.

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Jimbob

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Re: Another heating issue
« Reply #8 on: 05 April 2018, 15:40:41 »

So. Bin fodder? 

To be fair the heating will probably be dead by the time it failed again. But would have been nice to have a spare.

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Re: Another heating issue
« Reply #9 on: 05 April 2018, 16:19:23 »

I would be wary of that power switcher, given the fan has been running flat out all the time it may well be short circuit.

At a guess the mains is being full wave rectified and then switched by a thyristor or mosfet (the device in the heat shrink), those discs look more like transient suppressors to me and are known to be crap, if they fail then the power device will see all sorts of nasties and may well fail short circuit.
You beat me to it, Mark. Again.  ;D
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Kevin Wood

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Re: Another heating issue
« Reply #10 on: 05 April 2018, 17:32:57 »

Yes, if the fan's been running flat out, then something has probably gone short in the speed controller.
Could be fixed, undoubtedly, but not in 10 minutes. Keep it in case the boards are NLS next time, I'd say. :y
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Re: Another heating issue
« Reply #11 on: 05 April 2018, 17:49:50 »

Cheers all, make me feel a lot better going for the quick, expensive fix.

at least its not 5 mins soldeirng and 14p of components!

TheBoy

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Re: Another heating issue
« Reply #12 on: 05 April 2018, 17:58:29 »

I'm in a not dissimilar position, as my ecu is starting to play up again, but I knew last time would be last repair, due to the damage to the actual board :(

Do I pay £160 for a new one, or get a new board made, and hope I can lift the chips from the old one...


CBA is making me head towards £160 ;D
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TheBoy

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Re: Another heating issue
« Reply #13 on: 05 April 2018, 17:59:04 »

Though for now, a monthly press of the reset button is keeping us warm ::)
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