Potterton boiler pcb is as dave would say "wank" Im new so be gentle ;)

[connor.bisby]

  lets start with that face it explains it all. So if you read about the Potterton Suprima boiler on the internet you will find that seimens had a real shocker with this one. i am very much a beginner still so i have done a bit of probing about but nothing to extensive. the boiler when switched on works for around an hour till it locks its self out, so i thought well that sounds like a temperature issue so armed with my shitty DMM (wont say the brand name people will kick off ) i used the temperature probe on the transistor to see if it was that, now over a period of of 1hr i checked in increments of 5 mins and every 10 mins it was going up 10'c till the point it reached 60'c then the boiler locked out. If you see the pictures you will notice a tarnished area of the board directly above where the transistor is in its mounted state. I don't want to spend 260 pound (400.88 dollars) on a new board when i know it can be fixed i have scanned the internet top to bottom to find the answer to no prevail. so i have reached out for help haha defeated some would say, another reason i know it can be fixed is Ebay users are offering cheaper reconditioned boards at a hugely discounted price if you send the board to them in return, i can do more checks pictures and video if it helps anyone help me identify this problem. ohh and due to being a twat i forgot to take the pictures off my camera so the ones i have attached are sourced from Google but are very much the same issue.

[connor.bisby]

picture 2

[Seekonk]

The first picture looks like the zener diodes are cooking.  That transistor has a hole in it.  Nothing stopping you from putting a bolt through it and attaching some metal as a heat sink.  Though, I find it interesting because it seems to drive the igniter transformer and that is usually on only at the start.  Is there a probe at the flame, flames are conductive.  That may cause it to stay on.  The other brown on the circuit board is disturbing.  Measure the line voltage, it may be high.  Possibly the long term solution is to use a buck transformer to lower line voltage.

[DmitryL]

BTW, take a look at the second picture you posted. Zener diodes (or just diodes) lifted on their leads above the board to provide better airflow.
It may also help if you solder some sort of turrets (google for image "turret pcb") into the PCB and solder diodes' leads into the turrets

[connor.bisby]

sorry for sounding like a lemon but do the turrets help with heat dissipation as that could be a winner and also no the igniter does not stay on during normal running of the boiler it preforms its job correctly and turns off on combustion. and i will measure the line voltage and check the spec sheet of that transistor and those diodes, just wondering though is there anything in place there that would cause that to lock out if it was overheating, like any sensor or anything that's giving something feedback. excuse the crudity of that sentence i really am new hah

[DmitryL]

Also, check the crackled solder joints on the back of your PCB, this can lead to intermittent contacts.
For examples google images "solder joint cracks"

[connor.bisby]

yeh i have just stumbled upon a forum where a guy says just that quite interesting if you fancy a read, i have looked for this for a good while and only just stumbled upon it, cheers buddy
http://www.diynot.com/forums/viewtopic.php?p=302233

[connor.bisby]

picture of discoloration of the diode legs.

[bookaboo]

The smaller of the two green caps looks suspect there too. The bulge at the top is never a good sign.

[SeanB]

Well, they look like 400mW 12V zener diodes ( or 13V, depends on how lucky Potterton felt as to relay pull in voltage) driven with a capacitive power supply at around 50mA. The 0.6W dissipation per diode is what is the problem, especially as they used a 400mW zener instead of a 1W unit. Simply replacing the 2 zener diodes with 1W versions, spaced above the board like the originals, and replacing those 85c cheap electrolytic capacitors, the green ones next to them, with new 105C ones of appropriate value will likely fix the unit. that and resoldering the dry joints will make it work as good ( or better) than new.

[connor.bisby]

brilliant thanks a bunch and in regards to cheap caps what is a good brand of cap i was looking into this the other day? SeanB second time you have given some cracking advice thanks mate.

[connor.bisby]

ohh and i have a vici multimeter (cant afford much else yet) how would i measure the voltage pull of the relay and would it be safe to do so.

[Seekonk]

Doesn't it make you wonder why the transistor is getting hot if the igniter only works at start?  The quick answer is always popular.  Cheap modules like these often cook because the designer has to meet a low voltage spec,  Overheating components always last a while.  Entertain us and measure the temperature of the cap.  That 85C isn't the suggested operating temperature, it is the temperature they fail at after 4,000 hours.  A bad PS cap could be causing the micro to keep resetting.  I'd be designing the hell out of this.  You can probably get away with a few little things.

[connor.bisby]

well yeh priority is fixing it but i will have a little play with it first i could learn a thing or 2 rather than jumping straight on here and admitting defeat lol thing is i have read a lot of bad stuff about that cheap DMM vici vc99 and i worry when probing about shit that hurts when you plonk your finger on it haha. I will get a non contact thermometer and have a session measuring temps.

[GreyWoolfe]

brilliant thanks a bunch and in regards to cheap caps what is a good brand of cap i was looking into this the other day? SeanB second time you have given some cracking advice thanks mate.

Nichicon, Rubycon, Panasonic, Illinois Capacitor, etc.  Just don't buy off of eBay.  You will just be buying crap or fakes.  Buy from proper distributors located in your country. 

[connor.bisby]

ideal thank you i will take myself to Maplins tomorrow and get some bits

[Seekonk]

Even a cheap cap will last a couple years and I doubt a cap will solve your problem.  Right now you are just shooting in the dark.  It wouldn't be hard to draw out the power supply schematic and determine a couple points to monitor when it fails. 

[connor.bisby]

made a little video to show the extent of the bad joints and a picture of the zenner diode temp

https://www.youtube.com/watch?v=K9t2qF6l4LY&feature=youtu.be

[tom66]

Maplin don't sell good caps. CPC will stock the parts you need including good capacitors. £10 min order, free shipping.

[Seekonk]

At a place I used to work for some legacy products had crimp lugs placed on diode leads with the lug sections facing up as a heat sink.  I take a lot of things apart and am fond of saving the thin tinned metal used as RF shielding on old VCRs etc.  It is so thin it easily cuts with a sissors.  It works great as a heat sink soldered close to a diode body and a piece a half inch square can get rid of a lot of heat.

[SeanB]

With a 1W zener in place of the 400mW ones they will run a lot cooler, just from the larger body and thicker leads used. I have added copper plates made from dead relay contact terminals ( around 5mm by 20mm with a hole in the plate in the middle for the screw) soldered to the diode right at the body, and this cooled them down quite a lot. Here it is just that the original devices run very hot, and the capacitors next to them suffer from this as well, with the big one starting to bulge at the seal end.