Kingspan ASHP GMC board issue

[Gav_P]

Hi all,

 

I’ve been a long time lurker, but this is my first post on the forum... of course it’s because I have an technical problem that I need help with, and based on all the previous discussions on here I’m thinking there is more than enough experience to enlighten me!

 

I have a 4kw Kingspan Aeromax Plus KHP0041 (made by Carrier), heating my UFH system downstairs and radiators upstairs,  all was working fine until...it wasn’t.

 

I have 240v in the unit, but no blinking LED on the GMC board.

 

Now i’m not certain what the issue/cause is, but it might be related to the fact that I decided to wire in the alarm unit, so I could see from indoors if there were any issues without having to go out and open up the unit to look at the blinking LED on the GMC board. 

 

For some reason I thought it was a 0v feed so didn’t switch off the power and when posting the wire thought the wall I think I shorted it out... as I’m fairly sure it’s actually 12v.

 

So without giving me too much grief for being stoopid, do you have any other suggestion of what would cause the GMC board LED to stop flashing or how I could test it? Before I go and buy a replacement PCB.

 

In penance, I do have PDF copies of the Kingspan Installation Manual, the Carrier Service Manual and the Carrier Spare Parts document. If it’s of any use to anyone.

 

Thanks 

Gav

[Jeremy Harris]

Welcome.

 

I'm inclined to think that your guess that you've shorted the 12 V supply may well be right.   It might be possible to repair the board, but I suspect it might be hard, as there's no easy way to test any repair, and the chances are that there could be other damage, other than just the 12 V supply having blown.

 

I can have a look at the board in my unit and see if there's an on-board fuse in the 12 V supply, as if there is that may be a quick and relatively easy fix, as long as that's the only damage.

[Gav_P]

@JSHarris thanks for the quick response... I’ve popped the GMC out and can’t see a 12v fuse anywhere, so I think I’m going to have to suck it up and spend some money on it. I just begrudge spending £100 on a board when the whole unit was only £250 (new old stock).

[ProDave]

Can you post a high resolution (as high as you can) picture of the board?

[Gav_P]

@ProDave how’s that?

[ProDave]

Well there is the obvious fuse to check towards the bottom right of the board in line with all the connectors.

 

And a bit left of that is a tab power device that I am willing to bet is a voltage regulator, check if it is delivering the correct (or any) output. Clue, a pair of red wires to the connector "secondary" is no doubt the output from a transformer, there are 4 diodes that look like a bridge rectifier, and a big capacitor, all points to that being the DC power supply for the board.

[Gav_P]

@ProDave thanks. I’ve check the fuse, that’s the 240v that go to the transformer on the back of the board returning (as you point out) via the 2 red wires as 12v.... after that I haven’t got a clue. And not sure how to test any of the components. Plus they are all coated with something (I assume to protect it from the elements) so I can’t get my tester on anything.

[ProDave]

Measure with a DC volt meter from ground (0V) to the bolt passing through that tab power device sticking up from the board.  If the board has been hermetically sealed you should be able to get a connection onto that bolt.

[Ed Davies]

15 minutes ago, Gav_P said:

Plus they are all coated with something (I assume to protect it from the elements) so I can’t get my tester on anything.

 

It's called conformal coating. If you need to scrape it off to make measurements then you can get bottles or spray cans of the stuff to replace it. Better not to get it on connectors, though.

[Gav_P]

@ProDave Magic thanks... I’ll take a go at that.

[Gav_P]

@Ed Davies cheers. I wasn’t sure if I started removing it if it would do more damage or what to replace it with. 

[Triassic]

Just to be clear you connected a pair of wires to the board then threaded them through a hole, the bare ends touched and something went bang/pop? If it was 12v I’d start by looking at the twelve volt part of the board, transformer etc.

 

is there power to the board? You’ve not blown/tripped a fuse/breaker further back?

[Gav_P]

@Triassic sorry no, I wasn’t very clear. This board has an LED that flashes at 1/2hz when the unit is on, but it flashes different sequences if there’s an issue. However this board is inside the unit and you have to remove panels to see it. So there is an external ‘alarm unit’ that you can wire into it that can be sited somewhere more convienent (like indoors). 

So I connected the 3 wires to the appropriate connecting block (off to the right side of the PCB pictured here) and then poked the wires through the house wall. But because I stupidly assumed it was 0v I left it live whilst doing it. 

[Ed Davies]

The orange and black wires on the plug in J22 (between the fuse and the heatsunk device) - where do they go? To 23 and 24 on the lower connector block to the right? Does the book say what they are? General purpose 12V supply? Worth checking? Too long a string of suppositions?

[Gav_P]

@Ed Davies yes they go to 23 & 24 which is.... *rummages through the book* an optional external airsensor apparently.

[Ed Davies]

OK, weird that's by the power supply stuff when all the other i/o is on the other side of the board.

[Triassic]

I’m sure there was someone mentioned on here who did PCB diagnostics and repairs? 

[Gav_P]

2 hours ago, Ed Davies said:

OK, weird that's by the power supply stuff when all the other i/o is on the other side of the board.

 

The whole thing is weird to me. Never could get my head around PCBs and small electronics. 

Ive just double checked to make sure I didn’t make a mistake, but it’s definitely the air sensor.

[Gav_P]

52 minutes ago, Triassic said:

I’m sure there was someone mentioned on here who did PCB diagnostics and repairs? 

 

That would be nice... if they were cheap

[Ed Davies]

Can you see the part number on that heat-sunk device ProDave suggested putting a meter on the bolt of? Might have to unplug J22 to look at it. I'm thinking it's likely a 7812 voltage regulator or some modern equivalent. If it's a 7812 then the tab will be grounded so measuring the voltage on the bolt won't help much. If it's an LM317 or similar then the tab and bolt will be at the output voltage so a bit more interesting.

[Gav_P]

@Ed Davies Nice guess... it’s 7812B

[ProDave]

Don't see much any solder on that middle pin.

 

As viewed, left hand pin is Vin should read in excess of 12V, middle pin (and tab) is ground, and right hand pin is Vout and should read 12V

 

Simple checks to make. Careful not to short anything.

[Ed Davies]

… and careful not to touch any of those components below and left in that picture (GDT, MOV1 and neighbours like D5) as some are likely to have mains voltage on them. They're for protection against spikes on the power line, etc.

[Gav_P]

Hmmm not sure how i’ll get on poking around in such a small space with my clumsy hands and cheap tester.... but as Del says “He, who dares, wins Rodney!”

 

 

[Onoff]

Take a better photo of the label on the pcb and all the numbers etc on the board around it. There's people on here will take great delight in scouring the interweb thingy for a circuit diagram!