How to test a fan on a Worcester Greenstar 28i Junior

[hobbyist]

Well, I suppose I should thank you gentlemen for at least bothering to give answers of a kind. I can assure you though that in my case my engineer exists (and was not that cheap). He is of course a man of mature years, although the boiler had only limped just past its two-year guarantee.

Perhaps the question about the fan is more a hypothetical one than a real repair question, in that it would be interesting to know why it failed I haven't tried any testing yet, but the PCB isn't showing any visible signs of damage and does not seem to have been affected by water. Doubtlessly there are various electronic components on the PCB that could fail. In my limited experience (more in the domain of amplifiers etc. I admit) electrolyte capacitors are among the least reliable of components. I see most of the bits on this PCB are the newer surface mount technology, which is usually pretty reliable, but it does have several old style caps and an IC. If it is not secret knowledge, what components do you find are the most common cause of failure?

Incidentally the information about the readings on the terminals would not help do a repair but only tell you if you had succeeded and the device was now showing the right values. Remember I would not have been in a position to test it in a boiler.

Anyway I will leave you in peace.

 

[Dan Robinson]

I think the PCBs are the weekest part of these.

I am NOT an electronics engineer, so this is just a thought - I wonder if a worn bearing could have caused a component overload on the PCB? Meaning that even if the Fan PCB was repaired it would fail again fairly soon?

 

[Agile]

I see very few failed electronic fans because the type of boilers that I go to as an independent are usually older and I dont know anyone to give me old parts to play with!

There are several different types of electronic fan. Most that I have seen have been earlier types with the commutation on the fan and they usually had obvious burning on the PCBs and probably easy to repair.

But I would normally expect to fit a brand new part for as customer!

Electrolytic caps have a limited life ( often just 2000 hours! ) and are not usually needed in fan control PCBs.

Audio amps use them for decoupling in the PSU and for coupling to speakers etc.

Tony

 

[hobbyist]

I had thought I'd try to get the connection information before really looking at the PCB, but the fact that you chaps have put forward some hypotheses motivated me to take a close look. At the risk of getting boring I will report what I found. On inspection an unmarked DIL 24 pin device (with an integrated heat sink) has failed - not sure what it does, possibly switching or variable speed control. There is a visible hole in the IC body exposing the internal circuitry. Thus a repair isn't as simple as changing a cap, especially without information on the device, and the fan can go in the bin.

As far as I can see the bearings are fine and the fan,moves freely.

Just for info, there are two electrolytics on the PCB (the bigger more visible one is 68Mf, 400v), plus some ceramics and polyester caps. There is an 8 pin DIL LNK304GN AC/DC switching converter and a surface mount 10 pin IC, plus a cluster of surface mount components, and a rectifier.

 

[hobbyist]

P.S. For anybody interested, this is not a conventional DC fan but a BLDC (brushless DC) fan. It has a different arrangement of magnets and coils than the ordinary fan and different control arrangements. The two unidentified ICs seem to be a Hall-effect sensor and a fan control ASIC, and it is this last one that failed on my fan. I shan't try to repair mine, but it is interesting to know that a mere fan is quite complicated in this case.

 

[Agile]

I dont know what kind of DC motor you had expected it to be. Most as in computer cooling fans, cars etc. are brushless DC now.

Boilers need a known but variable speed fan.

There are two main methods to achieve this.

A DC motor whose supply is controlled be comparing the measured speed with the required speed.

Or the syncronous AC motor with three or four poles which is similar in concept to a stepper motor on a printer. The frequency ( or better the commutating signal ) is varied acording to the speed required.

Tony

 

[hobbyist]

I suppose my mention of conventional fans picked up on your mention of older or early versions. My lay person's guess is that most newer ones are BLDC and the two approaches are ASIC control or micro-processor control. Incidentally the DC (and the need to rectify and regulate voltage) is why (I suspect) there are electrolytics on a lot of these, contrary to what you said.

 

[reapairman]

the fan in my rd532i worcester boosh packed up a few days ago.

took it apart and the bearings have gone, the pcb around it has browned from overwork in places.

a new fan - £180! - ffs!! for the sake of a couple of worn bearings.

looking for 2nd hand replacement, it's a ebmpapst rg130/0800, funnily enough the same fan mentioned in the original condensing boiler patent of 2002
http://www.freepatentsonline.com/6401669.html

i'm tempted to attempt a bearing change myself.

hobbyist, for a layman as you describe yourself, you have a decent knowledge of electronics.

 

[Gasguru]

Looks like another pointless patent...everyone's doing a similar thing, with another dog of a heat exchanger that will clog up and is impossible to clean

Apart from bearing failure (ball race or sleeve) I think you'll find a lot of fans fail due to the impeller stalling and surge currents taking out the drivers.

On the Worcester this is often the case...the 10R fusible resistor feeding the inlet filter network goes open circuit probably as a result of a stator coil driver shorting.

 

[reapairman]

thanks for replying gasguru, indeed that 10R resistor is open circuit, it had flaked off a bit but didn't have a meter to test it yesterday. just checked it just now and yeah, it's open.

would be nice to study some motor controller schematics to see exactly what is going on inside.

might give ebmpast a call to see if they have any replacement bearings ; )

 

[Agile]

It would be nice to have any information at all on boiler parts.

Sometimes they scratch off the part numbers on components!

Unfortunately the makers just dont provide them!

I suppose why should they? They dont want them repaired do they? Nor do they want their design copied!

Tony

 

[hobbyist]

For 'reapairman', I did see this refurbished product (may not be right model for you), although I forked out for a new one myself via my service engineer (not cheap).

http://www.allsparesdirect.co.uk/index.php?main_page=product_info&products_id=613

I have no idea if the company offers a good product, but it does seem to provide the same one year guarantee that I got on the new one. You have to buy on an exchange basis.

 

[reapairman]

thanks hobbyist, yes I saw this yesterday and so far it's the cheapest replacement. quite a few almost the same number fans on ebay for approx £20 including postage, so just a matter of waiting till a matching one turns up.

Called up embpast in germany, got speaking to a friendly german guy, who was pretty helpful and nice to talk to, but cos of red german tape etc, he wouldn't tell me the bearing spec/numbers.

anyway, I decided to strip the thing in entirety.

the bearings are 626Z1X type and are about a tenner each, although people are flogging the 626ZZZ version (not high temp) from £1.50 on ebay as boiler fan replacements.

only one of them seems knackered and it's also dented in 2 places, dirty too. I'm going to see if I can pick one up now locally and see how I get on.

 

[Agile]

Make sure you can get the impellor off before you buy the inner bearing!

What is a 626ZZZ ?

Normally a ZZ means two metal shields !

 

[reapairman]

yeah the impellor was the easy part!

the tricky bit was getting the cooling fan off to find a tiny circlip and removing that intact without tiny circlip pliers. then removing the bearing protector/locating seals, divoted in place.

I'll post some pics if you like.

the extra Z on the end of my 626ZZZ was cos it was well tired, the things knackered.

will put it all back together tonight and see what happens.