Desoldering a transformer

[Bobsound]

I am repairing a Drawmer compressor unit. The mains transformer has an O/C primary. It is mounted on a double sided board and I am concerned about lifting the lands on the component side of the board while trying to desolder the transformer. Do any of you have any tips to avoid causing damage? I have been using a solder sucker, at the moment the transformer shows no sign of wanting to budge and I do not want to force the issue.
Many Thanks
Bob

[John10b]

If you could post a picture this might help. In the past I have cut out the faulty component to avoid doing any unnecessary damaging.
John

[AC/HL]

Flooding the joint with fresh solder, getting it nice and hot and getting a good seal with the sucker usually works for me. Waggle the pin a bit with the iron to make sure no whiskers remain. Earth planes are the worst. One leg at a time of course.

[Diabolical Artificer]

Nightmare! Can you get in to cut it out? With difficult jobs like this I usually wedge a screwdriver under the components to be unsoldered and lever gently using a very hot iron quickly applied using lots of flux and fresh solder.

Andy.

[1100 man]

Hi Bob,
Agree: nightmare!!

I had the same scenario with the PCB from an electric winch. The transformer had 12 pins on double sided board. I tried all the usual techniques: solder sucker, braid, screwdriver under transformer etc, but the pins were a snug fit in the holes and to make matters worse, it was lead free solder

In the end I cut the transformer out of the board by cutting through each leg. This was very brutal and took some time to avoid damage to the surrounding area. It worked fine though and no tracks were damaged.

Of course, soldering in the new transformer with lead free solder was a pain....

Good luck
Cheers
Nick

[Bobsound]

Thanks for your replies. The transformer is tightly fitted between other components and there is little room to ge a pair of snips in to cu the tags. My first priority is to see if I can get a replacement from Drawmer! I think i have uploaded an image but I can't be certain!
thanks
Bob

[Trigon.]

Desperate times, desperate measures..

1: Hacksaw/angle grind off the visible parts of the windings and cheeks, flush with the steel.

2: Lever cheeks away from core to break varnish bond.

3: Pull off laminations to (hopefully) improve access to terminals, allowing them to be cut.

Cheers

[KeithsTV]

Turn the board upside down and use a heat gun to blow hot air over the transformer pins. Keep the gun moving and not to close to the board and it should melt the solder on all the pins and with a bit of luck the transformer will just drop out or it will be loose enough so it can be gently pulled off the board but be warned it will be hot.

If it's a double side board with plated through holes do not be tempted to pull the transformer off unless you are sure the all the solder has melted.

I successfully used this method recently to remove a relay from a double sided board.

Keith

[Ed_Dinning]

It is also possible to make up a copper block to fit in a large (120W) iron. This should have holes drilled at the terminal pitch. Similar units were sold to work on up to 24DIL IC's.

As it is a repair to existing you may not need to use lead free.

Ed

[John Caswell]

Just taken a couple of 14 pin relays off of a Krell amp PTH board.
The only safe way I could see was to cut the relays to bits and remove each pin individually. Worked a treat - refitted the relays in sockets, which I now do as standard if there is room
I think you are going to have to trash the transformer to save the PCB.
Any idea what the rating and voltages are, as you may be able to replace it with a toroid with leads. Trigon,s method is a sensible way out of this

John

[Diabolical Artificer]

Whilst trying to remove this, check to see if heating the primary pins has fixed the OC fault, you never know your luck.

Andy.

[Bobsound]

Thanks everyone for the further suggestions. i might try the heat gun approach first and ten resort to the more destructive techniques later;
thanks again
Bob

[turretslug]

I'd go along with Bill'S (AC/HL) suggestion of irrigating with fresh solder and slurping out as much as possible, then playing the heat gun over it, as the minimal amount of solder left behind will melt quite quickly without having to get the bulk of the board too hot,

Colin

[Bobsound]

As a postscript to this thread; the transformer arrived yesterday and I have just carried out the replacement. A heat gun worked superbly, the transformer pulled straight out. Unfortunately I managed to burn a small patch of the PCB to the extent of carbonising the fibres beneath the resin so care is certainly needed! Many thanks for the advice, I think this thread can be closed.
Bob

[Radio Wrangler]

Check for an embedded thermal fuse in the primary winding. Some of these can be weedled out and replaced. Not many, but it's worth checking.

David