Brother P-Touch 1230PC
Repair
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After re-arranging my stocks
of spare parts I needed to produce labels to stick on the various
containers. Many years ago I'd purchased a label printer and
a roll of special tape. It had worked perfectly well but, when
I checked it recently I found the six batteries were bad. All
bar one had reduced voltage but one had leaked and blobs of crusty
deposits were visible on the contact holding the leaky battery.
I cleaned it off easily because the springy material seemed to
be stainless steel. I fitted a set of new batteries and pressed
the ON button. Nothing happened so I removed the label cartridge
in case it was causing the problem. This allowed the green ON
lamp to illuminate and flash but went out when releasing the
ON button.
An e-mail to Brother indicated
there was a power fault and the device would need servicing so
I decided to open it up and see if anything was obviously wrong.
I could see lots of traces of verdigris. The traces were around
the area carrying power supply components and as you can see
below many plated-through holes are affected. |
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The first job was to clean
away the verdigris, then check that each hole had continuity
between circuitry connected by the plated through holes. Some
20 to 30 holes were affected, seen by shining a strong light
through the board. About 50% of blocked holes were affected,
although the remainder carry solder. Surprisingly, all the holes
measured OK so I started checking surface-mounted components.
All appeared to be OK except for the small SOT323 device labelled
"NG" whose resistance readings were suspicious. Checking
the code I found the device was a CH3904WPT. This is an NPN transistor
rated at 40 volts and 200mA. This is faulty, with its test readings
having no resemblance to a good NPN transistor and oddly the
connection between the collector (the pin on the RHS of the chip
above) had no continuity to the one hundred ohm resistor marked
"101". Even with strong magnification the track looked
OK, but it was open circuit at the point were is passes to the
resistor mounting pad. |
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Above, I've replaced the
SOT323 transistor with a BC817 which is in a slightly larger
SOT23 package (sorry it's blurred) and the track to the resistor
is clear, but actually open circuit. |
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I fitted a wire link to
replace the track and, as everything now tested OK with a meter,
I decided to refit the board. Below is a view of the board as
seen when the four case screws are removed and the lid detached,
board removed and wiring detached. |
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And below the opposite
surface to which all the wiring connects. |
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Above with wiring disconnected
and, below after the repair, I rewired it. To help, the board
carries markings indicating wire colours as one would expect
except K=Black and C=Brown. Red/Black are used for the motor
(very thin), a micro-switch (centre) and battery leads (next
to the switch). The flexi-strip has its conductors facing to
the board centre. |
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Below, the circuit board
is mounted using a single screw (bottom left). |
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After refitting the case
and inserting six new AAA batteries I plugged in a USB lead and
pressed the ON button. The green light stayed on and I printed
the first of many labels. |
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