Osram Quicktronic QT 1×58 Modern Dimmable Fluorescent Light Repair
This short repair is about an Osram Quicktronic QT 1×58 modern dimmable Fluorescent light (58Watt upto 70Watt tubes). A friend of a friend has a Turkey Farm where they have collected a lot of these defect electronic quicktronic devices. And over time a couple of them end up at my place for investigation on why they no longer do work.
Most of them in the past were corroded by moisture caused by regular cleaning sessions when water got into the light controller circuits. And others in the past stopped working simply because the 10uF 460V capacitors had broken legs or broken cilinders. The latter were easily fixed by replacing the e-caps, but in the newer board versions the now new 500V 10uF capacitors no longer are causing any problems.
Previous photo shows the 230V transformer L1 that is fed by the 230V AC input voltage on connector pins 1 and 2. And next photos show why this device no longer was working.
On this board there were 2 special safety fuses integrated on the pcb solder side surface in the 230V input tracks. So not the usual glass type or plastic type of fuses anymore! And one of the input line printed fuses had completely vaporized. As also was indicated by the spot that was left on the plastic inside foil after the special print fuse melted which is shown on another photo. The diode bridge rectifier was conducting in one direction on both its ~AC pins. My DCA 75 detected a single diode there which clearly was wrong. The 230VAC transformer tested okay!
The 230V AC transformer clearly was not the reason why one of the pcb fuses blew. As above photo obviously proves. It indeed was the diode bridge right after the transformer that caused the overcurrent. The 3 marking on the pcb solder side on above photo on the right is the position where the 1…10V transformer is placed that regulates the Dim function. I could detect a good output function on this transformer with my Blue Ring tester but the 2 closer input pins did not show any measuring.
After I replaced the diode bridge with a good one from another Osram quicktronic pcb, I tested the 230V input and measured if the 10uF 500V e-cap did charge. It showed about a perfect 324 DC voltage.
I also checked the other transformers and they all tested fine with the Blue Ring tester. And I also tested a couple of the semiconductor N-channel Mosfets with my Peak Atlas DCA 75 Pro which only could be done after removing them from the board. As testing in-circuit was not possible and only resulted in a “No object detected” message.
In the past most of the replaced 10uF 460V capacitor defects worked afterwards. And since I do not have the FH21W 85CM tubes nor the external dimmer circuit I hope that also this repair will work.
Next photo shows another QT 1×58 board that has a slightly corroded Dim circuit on the right from the previous mentioned Dim transformer. But strangely on this board the transformer is marked position 6. After I cleaned it with an old toothbrush and some gasoline (Dutch: wasbenzine) it showed no signs of bad tracks or bad components.
Here follows the datasheet of the defect diode bridge a single phase 1A 700V RMS rectifier:
Repairing products like these without any service manual or circuit from the manufacturer is never easy. So I hope this repair at least contributes in fixing some of the 230V AC input problems on the
Quicktronic Osram 1×58 FH lamp controllers. And especially about the uncommon safety fuses that are used in this product.
Albert van Bemmelen, Weert, The Netherlands.
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Note: You can read his previous repair article in the below link: