@julesmp8 After a whole battery of tests? 😉

Well the unit has been repaired and returned after what must have been literally a few hours back at Immersun.

I asked for a detailed service report and got this:

"Multiple fairchild transistors and 1x T3 Transformer was found to be non-responsive via extensive repeat testing protocol, they appear to have been overloaded at some point in prior operation"

I have yet to replace and recommision it but hope this is the end of the saga for a long long time. 

I will probably change the immersion heating element and stat too as a precaution.

Jules

@julesmp8 fingers crossed.

I have to say our Immersun is quite noisy with loads of weird high pitched sounds and buzzing coming from the various components. By extension our Solar iBoost was completely silent.

@editor Hi, I helped fix a friend's Immersun recently. He had completely removed it and when we provided power it showed an error code. I took out all 4 of the big power transistors and tested them with a multimeter, just measuring resistance between collector and emitter, in either direction. One was open circuit, we found some in the same series but with higher capacity (current). My friend bought 4 of them and I soldered them in which fixed the problem. We went for the transistors because he had read on a forum others had blown. If I didn't know that I would have gone for the electrolytic capacitors first. NB there was no visible sign of the fault (no charring etc). The Immersun was just out of warranty and I think they wanted £160 just to look at it!

@mikeavison that's a great fix. Well done, and £160 - transistors saved.

I don't suppose you took photos of the transistors you replaced as an additional reference to this post?

@editor Hi, not as clever as you might think! In taking a picture for you I now note that the four we took out were not identical but having reviewed the data sheets of them both I think they were so similar they probably came out of the same storage bin at Immersun and randomly installed. In my defence, I was in need of laser eye surgery at the time to clear some scum which was impeding my vision and the text on these transistors is very faint unless you get the light at just the right angle. Unfortunately I don't have a note of the ones we replaced them with but I have sent a message to my friend (who I was mending the Immersun for, and who ordered the replacements) and I will post again if he can remember the ID.

The data sheets of the 2 types we took out are at:

ONSEMI.COM "https://www.onsemi.com/download/data-sheet/pdf/fgh40t65updcn-d.pdf"

and  https://www.onsemi.com/download/data-sheet/pdf/fgh40t65spdcn-d.pdf

I suspect the ones we put in might have been something like:

https://www.onsemi.com/download/data-sheet/pdf/fgh60t65sqd-f155-d.pdf

Which has similar characteristics except is able to handle 60A instead of 40A

I hope this is of some help.

PS Incidentally, just for interest, these transistors are a sort of hybrid I had never heard of before Insulated Gate Bipolar Transistors (IGBT). The input is like a MOSFET and the output is like a bipolar junction transistor. 

Addendum / correction : we have checked the ID of the transistors we used and they were FGH 50T65 UPD. I used 4 of these to replace all 4 of the large transistors in the unit, i.e. the ones in the photograph above. It was about a month ago and still working fine, of course I don't know how long it will carry on for but I expect it will outlast a unit with the original transistors since these have a higher rating (50A compared with 40A). If you have a broken Immersun it might of course not be the transistors that have blown but reading blogs elsewhere it seems to be a common cause of failure. You can check before you buy but it does mean unsoldering, then you only need a multimeter to check them. If it is not them I would replace all the electrolytic capacitors (they are not expensive). There is not easy way to thoroughly check electrolytics, you would have to feed them DC with ripple at or near the specified maximum voltage and then measure the leakage as they got hot, not really worth the effort, just replace them.