240V-120V=Magic Smoke JBC Edition

[SeanB]

Funny enough, reminds me of repairing a very very expensive Bioptron lamp, which I bought on auction on a whim, because it was cheap, and I thought it looked cool. Automatic mains voltage selection, which they achieved in a rather interesting way. Light provided by a very well designed and built SMPS that did the input AC rectification, smoothing and conversion to 12V DC very nicely, just needed a startup supply to power the control electronics in it, which also was used to power the timer for the unit. 100W halogen lamp, and a cooling fan for it.

Powering the low power digital timer was the interesting supply, they wanted a power supply that was universal, which the main lamp power supply certainly was capable of handling, but they did not want to put ( or were size constrained on the board by then) a small switcher in, so instead they put a simpler method. Not capacitive dropper, but instead they put in a 230VAC to 24VAC 2VA potted transformer, and a bridge rectifier on the output, and a 470uF 63V capacitor. All pretty common, and then they put the voltage regulator, a single zener diode, 12V 0.4W, a resistor from the supply to feed it around 1mA (22k) and a Zetex darlington, which was expected to dissipate over 1W in the 230V position. On a 120V supply the regulator still works, providing a nice 12v rail and only having a tiny power dissipation, but on 230V it ran hot enough to discolour the board. Fault was that on 230V the transformer was somewhat overloaded, and burnt out. Google told me, via translate, that the transformer failing, along with the little Zetex transistor melting itself off of the pcb, was a common fault.

Little Zetex was fine, just somewhat changed colour wise from the original, with brown instead of white printing. Transformer was open circuit on the primary, and looking underneath the potting was somewhat cooked. Replaced it with a 12V one, and drilled a single new mounting point for it to fit the one leadout, and it works fine. Still sitting unused, no need for a lamp that has snake oil all over it, and which makes a good room heater, and a very inefficient polarised light source.

[robert_]

Also, I forgot to mention that the secondary side of the transformer does have TO-92 looking component with 1 leg cut off. I haven't looked to see what it is, but I will get to it in the rewind or when I get a new transformer. One leg shares a connection with the 12v winding.

Should be an LM335. It monitors trafo temperature as the transformer cant supply maximum heating power forever at high ambient temperatures.

I got a "faulty" station for 10Eur some time ago, for some unknown reason that part was shorted and it caused some error message and no heating. That was quite a cheap fix. Seems as if the station works with it not being connected, but it does fulfill a safety function, so it should always be replaced.

[FRR]

My main point of posting this is of course for educational purposes. Part of it was to also show that a fuse is not really inside of the equipment to save the equipment. This is also not a bash on JBC. I own / have owned stations from JBC, Pace, Hakko, Metcal, and Weller. Of all the units I have owned I never had any complaints about design, build quality, or components used (other than the crappy Hakko UI).

Just an update, but I have not heard back from anyone allowing me to purchase a replacement transformer. A simply no we will not sell you one would have been enough as well. That means this project will continue with the disassembly of the transformer, removal of the primary winding, and rewinding the primary side of the transformer. At the same time I will inspect the secondary and rewind that side as well if needed. I will take pictures of the progress and post once I have it completed. If anyone has any specific requests of parts they want to see now is a good time to ask.

[webcobra]

Hi. I have such a JBC station for 120v completely working. I need to use it on 220v. I want to replace the transformer from 120v to 220v, therefore I am looking for a transformer with primary winding for 220 and corresponding secondary windings of 23.5v and 12v. Is it possible to find it? Can anyone have such a transformer from a non-working station? I need the same for only 230v from CD-2BB / CD-2SB 230V.
I connect a JBC station through a 220/110 transformer. It works fine, but I would like to redo it to 220v.
I found a similar in size and power transformer 230v, only the secondary winding 2 x 12v. Can be used to power the board as 12v and together as 24v to power the heater. What do you think?
And what about the temperature sensor on the transformer? Should it be installed after replacement too?
Thanks