Electronics Ballast Repaired
The St. Kilda Repair Café in Melbourne, Australia provides a free service to the community for the repair of household items of all kinds, saving them from being sent to landfill. Staffed by volunteers, it operates on every second Sunday of the month.
A recent item presented to me for diagnosis and possible repair was a three fluorescent tube fish tank lamp, which the owner reported as not working on any of the three lamps. A quick test confirmed this, so investigation began by removing the tubes (which were independently confirmed as operational) and observing that the Ballast needed to start and run fluorescent lamps was all electronic.
The electronic ballasts were in three aluminium channels (one per tube), so to get an idea of the scope of the problem, one was removed for diagnosis. The printed circuit board is narrow and long, but all the components are old style through-board types and therefore readily examined.
The two photos show part of the component layout at each end of the board.
The Repair Café has little by way of electronic diagnostic equipment, so I took the lamp home for further detailed investigation.
It didn’t take long to identify that the two high voltage transistors, type MJE 13003 (QV1 and QV2) were both dead, as were the two high voltage electrolytic filter capacitors (15uF, 250volt), as well as most of the resistors. There are two 1.5 ohm, two 15 ohm quarter watt carbon resistors and two 680 k ohm 1 watt carbon resistors on the board, all deceased except for one of the 680ks.
That was the outcome for the first board examined.
The ballast is essentially a Switch Mode DC to DC converter that provides the high voltage necessary to start the fluorescent tube.
As I was unable to source the high voltage electrolytics and the transistors locally, I contacted the owner to confirm that he was prepared to wait for overseas delivery of these devices. The cost was quite low, but the wait time likely to be 6 weeks. The owner was keen to have the lamp repaired, so orders were placed for the long lead time components and locally sourced resistors were purchased.
In the meantime, there were two further ballasts to be diagnosed, and the same damage for these was expected. What a nasty surprise when the next two boards were autopsied. Both had signs of large current flow through the full wave mains rectifier, with exploded trackwork evident.
The diode types used in the full wave rectifier are types 1N4007, and although only two in the bridge on each ballast were shorted, all were replaced as a precaution. The likely cause of the overload is suspected to be water vapour condensation, but there is no confirmation for that. The exploded track was bypassed using the replacement diode leads as shown. Ugly, but effective.
At the completion of the long wait for the high voltage parts, all faulty components in the first board examined were replaced, with all other parts checked in the process. This board was then hooked up to a fluorescent tube and a 240 volt ac mains lead was attached, then in a safe (outside workshop) environment, a “smoke test” was conducted.
With confidence thus gained, the remaining two boards were also repaired and tested individually prior to reassembly of the three-tube unit, and a final bench test.
These lights are very bright, and very purple to assist with water plant growth.
The completed item was returned to the customer, and since I have heard nothing further from him, it’s assumed he is happy with the outcome.
Roger Owens is a retired Electronics Engineer from Melbourne, Australia who enjoys exercising skills learned over many years in hands-on roles in Communications Engineering. Volunteering at the St. Kilda Repair Café provides an interesting and rewarding outlet. A strong hobbyist interest in all things microcontroller helps with diagnostic and test techniques. At age 72, there is always something new to learn.
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