Hi guys,
Great forum, always find something useful here.
Recently opened my europlus psu to see if any caps needed replacing and found that the mini transformer T3 in the middle of the board is part melted on top but only smells a bit, not seen this before and can't find any information about it. The computer works fine with no burning smell when used. Can't tell how recently this melting happened but as this astec part seems very hard to find just wanted to check if it's still safe to use.
Any advice is much appreciated thanks.
I wonder if that's just the outcome of 40 years of time and the material has degraded. Hard to say from here.
Hi thanks for your reply.
Its a strange one but all the photos you find of open psu's don't seem to show any marks, look at the forum post about the Aussie psu for example.
Can't understand what would cause the mini transformer to overheat to cause the marks, the burnt smell is very slight and everything works just fine.
As mentioned my main concern is just is it safe to use it.
Have added a couple of photos to show the whole board and a closer view of the area in question. The board looks fine, confused on this one.
5EFE4FC2-645A-4FE9-A49D-52BCFD269B26.jpeg
94E6FBF2-48E6-4C86-9787-4C820C3154B2.jpeg
Just to add the burnt rifa capacitor on the left has already been replaced since the photo was taken and the Apple was turned off within a minute of it starting to crackle. Not sure if this would affect the T3 transformer.
The Rifa is in parallel to mains. If it opens, nothing happens. If it shorts, it'll burn but shouldn't affect anything else on the circuit as it will take all the current. I cannot comment further unfortunately, I am not familiar with that version of PSU.
The small transformer T3 is never really under any significant load. It's just there to transmit the feedback signal from the secondary side back to the primary side. Only a marginal current will be transmitted by T3, just enough to switch the two primary side transistors (Q1, Q2). I couldn't see how T3 could be overloaded. I guess the transformer always looked like this - or material has degraded.
Couldn't the faint burnt smell also still result from the blown RIFA cap?
MacFly,
So is that the equivalent of a modern optocoupler?
Yes, a modern design would prefer an optocoupler to transmit information (not power) between galvanically isolated circuits (nowadays a lot cheaper and smaller).
Should be fine. If you mean the slight bubbling on the moulded surface, that could have easily been they from the day it was manufactured. Smelling slightly burnt tends to be normal after decades of heat transfer, but that smell should not be evident if the PSU is sealed.
Hi guys,
Thanks for your replies, the psu was unopened when I got the system with the white wax bits intact on the psu board screw head so looks like nothing done to it before. I did strip down the Apple II when I first got it just to make sure everything looked correct and at that time the RIFA capacitor had no signed of cracking but for the life of me I can't remember what the T3 transformer looked like so yeah it could have been like that for a while and being 40 years old I guess a bit of a smell should not be a concern, did not sniff the larger transformer at the time for comparison but will investigate further when I service the keyboard in the near future as some of the contacts need cleaning, age again.
So basically this should be safe to use as it is but worth keeping an eye on the T3 to see if the area looks more melted in the future however from what I understand the part should not normally get hot enough to melt so bit confused on that.
Thanks again for the advice on this and I will update when I have further info in case other users have a similar issue as could not find anything on this when I searched so maybe helpful to others.