Author Topic: Bioptron lamp repair.  (Read 5102 times)

SeanB

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Bioptron lamp repair.
« on: April 26, 2015, 01:12:52 PM »
I posted on EEvblog the teardown of this auction buy, so here is the repair.

http://www.eevblog.com/forum/reviews/bioptron-light-teardown/msg659921/

So on inspection they make a power supply for the electronics using a small 2.8VA transformer, and then to make sure it will work with the full input voltage range of 100-240VAC they simply burn off the excess voltage in a small Eline darlington transistor. Such a small package, and they expect it to do so much work.

http://www.diodes.com/datasheets/ZTX600.pdf

ZTX600 power darlington, rated at 1W power dissipation, and with a 160V spec and 1A capacity. Only problem is that with a 240VAC supply you have a little over 1W of power dissipated in this transistor so it runs very hot, cooking the board in the area around it. Apparently a common fault, the transistor dying and taking out the 18V zener diode used to make the supply as well. My one the transistor and zener are still fine, zener is 18V or so, and transistor has a very high gain within spec.

The lamp is driven with a standard switching power supply, using a now obsolete ( but still available from the second source makers) UC3845 switcher, driving the lamp with 12V.

http://www.onsemi.com/pub_link/Collateral/UC3844-D.PDF

The failure was the other common one apparently with these units, the little transformer cooking itself. My one did blow itself apart internally, with the top of the gray case having a brown bulge of cooked resin, and a split at the bottom that let the magic smoke out.



So, after removing the new used transformer, from some old industrial logic I got at auction a good number of years ago for almost free ( IIRC I paid R20 for the lot of around 200 plug in assortment) and figuring that it will no longer work on 100VAC ( and I do not care, it will stay cooler on 220VAC with the reduced supply into the regulator, 24VDC as opposed to the original 40VDC)is not a problem. The regulator will stay cooler as well, it should run barely warm.



Install new black transformer, and add the one wire link needed to make it work and time to test it to see if it works. Temporary test with a 20W halogen bulb, just in case it was going to blow up the original 90W 12V halogen lamp. Plug in the IEC cord and the display turns on. Igor, The Creature is ALIVE!

http://www.youtube.com/watch?v=1qNeGSJaQ9Q



So now all that is left is to replace the test lamp with the original 90W one, and put back into the case properly.  Then a test, and it glows yellow, though I have no idea if it works, my foot does seem to feel better after a 30 second therapy session. Just have to go get the stand and put it together.

« Last Edit: April 26, 2015, 01:17:08 PM by SeanB »