PCB track repair 101

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marantz123

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I will be documenting the repair of a printed circuit board from a Sansui AU101 which has been through at least four repair shops in its lifetime (judging from the repair job number labels) and was condemned to the dump, beyond economical repair, when in a moment of luck (for its own good), one of our forumites ran across a busy street to stop a clearing team from throwing it into a dumpster. The unit was advertised here ( https://www.avforums.co.za/index.php/topic,82286.msg948218.html#msg948218 )  [member=14513]stormbringer101[/member] and I was fortunate to receive this. The unit was said to be working, however did not consider powering it up after assessing its condition.

I searched our forum and other locations for information on PCB repair and haven't found much information, and whatever I did find required expense and was without the much needed advice concerning the technique required. I will be focussing specifically on the restoration of the amplifier PCB. This particular board is the last (third) revision of the board/circuit. The preamp board has not been messed with and that is a relief.

The methods revealed will permanently restore a board, and the repaired areas will stand up to another 40 years of rookie repairers with the repaired tracks and solder pads  never lifting again unless intentionally abused.

External cosmetics are not too bad as can be seen, some chipped veneer which has been replaced already, a broken power switch (internal bakelite cam and AC solder terminal) which was severely abused, has been successfully reconstructed and repaired, a faceplate in remarkable condition considering other aspects,  all knobs and switches present, some damage to the bronze-coloured metal trimming at either end of the faceplate. Rear panel as dirty as the front, but internally the unit is much dirtier and grimy than the outside.

Internal cosmetics, would reduce a Sansui lover to tears. The sight of the damaged power switch, the shorted/bypassed power connection twisted together without any solder, a very, very dirty chassis, and an amplifier PCB in a state where tracks were "torn" off the board, solder pads missing, components (output capacitors, transistors, power diodes) on the paxolin PCB connected with wire jumpers, floating without any support from the PCB, and dozens of solder pads lifting away from the pcb, not to mention a damaged power cord and all fuses bypassed with stranded copper. It seems that a recap was attempted at some stage and was eventually abandoned as the damage to the board escalated.

This article is intended to empower anyone to perform their own PCB repairs, professional-looking quality work at minimum expense, with lots of pictures and will cover the tooling required, making of new copper tracks easily, creating new solder pads and mechanical support for components with the finished results as good or at least electrically better than the original board, all with commonly available materials and tooling, except one small multi-purpose insertion tool which you will need to make from a regular paperclip. All of this is my own home-brew method, from earlier failed tooling and choice of materials where turn-around time to produce a solder pad/restored connection took more than 40 minutes is now reduced to under 10 minutes per connection with room for improvement to be obtained with better tooling or methods. Technique is something that isnt often disclosed and I plan to cover this, as well as I can.

Current progress :  the chassis has been carefully washed, power switch repaired and its design improved to prevent a re-occurence of its failure, the electro-mechanical repairs to the board is at about 90% completed, spanning 64 new solder pads and a handful of track repairs. Still another 10 solder pads to consider, with 8 of them being those of the output transistor solder pads currently hidden under solder and their state still to be revealed. Economically, the time and effort in this restoration of an entry-level unit is a loss, but this is a wonderful opportunity to develop this skill, showcase it here and be better prepared for more valuable restorations.

Watch this space, and please bear with me as this may take some time to kick off properly.

Best regards
Marantz123.



 
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