Brother P-Touch 1230PC Repair

 

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.

 

 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.

 

 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.

 

 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.
 

 And below the opposite surface to which all the wiring connects.

 

 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.

 

 Below, the circuit board is mounted using a single screw (bottom left).

 

 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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