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Serviceman's Log

A little knowledge can be a dangerous thing - or so goes the old saying. However, some people just can't help themselves. Some jobs should definitely be left to a qualified serviceman.

by the Serviceman

Items Covered This Month

• AWA-ST03 tuner

• Washing machine solenoid

• Rescuing two old organs

• Fixing electronic scales

Why do people who know absolutely nothing about electronics or electricity risk life and limb by delving into the depths of mains-powered equipment? This next story from D. S. of Maryborough, Qld tells of one such incident that could easily have ended in tragedy . . .

I recently went to pick up my son from the home of one of his school friends, after he had spent some time there. When I arrived, I was greeted by the man of the house who immediately began seeking my advice on some electronic gear.

It transpired that his problems all began after he had visited the local recycling centre. He had purchased an AWA component system consisting of a record turntable, a dual cassette deck, a CD player, a tuner and an amplifier. He paid the princely sum of $20 for the lot and, grinning from ear to ear, brought it home.

Unfortunately, he then discovered (upon plugging everything in) that the tuner was faulty. And so, ever the optimist, he removed the case and began looking for whatever was causing the lack of life in the tuner.

The tuner had a small filter network for the mains input and this was safely tucked away under a shield. A sticker on top clearly warns of the dangers of removing the shield when the unit is connected to the mains – which is precisely what he proceeded to do!

He then discovered that the GPOs (general purpose outlets, or mains sockets) in the lower section of his house were NOT covered by the home’s safety switch – something he found that out the hard way when he received a severe electric shock! That put paid to any further delving and when he discovered that I was soon arriving to collect my eldest son, he decided that it would be best if I “could take a look at it”.

Click for larger image

Well, look I did but this initial inspection revealed nothing obvious. In the end, I told him that I would take the tuner home and have a closer look in the morning.

The tuner turned out to be an AWA ST-03, a neat little unit from a bygone era. Inside the chassis was the aforementioned mains filter, a small transformer, a main PC board and the tuning assembly. This assembly consisted of a tuning gang, a dial cord and an illuminated pointer, etc.

I began with the mains filter but there was nothing wrong there. The transformer was also OK, so I turned my attention to the main PC board.

Closer inspection (with my eldest son looking over my shoulder) revealed nothing untoward except for a TO-220 transistor that was cocked over at a bit of an angle. Normally, this is no indication as some components are installed this way to clear other parts. In this case, however, there was plenty of space and I also found the transistor to be quite loose, as it had no heatsink for support.

At this stage, I had no choice but to remove the PC board. This involved removing nine screws from the board itself, the front fascia panel, the knobs from the three pushbutton switches, the large tuning knob, the dial cord and the main pulley from the tuning capacitor. Getting the board out was a tight squeeze but the connecting wires were long enough to allow me to flip the board over and inspect the solder side.

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