Repairing a printer: HP DesignJet 110plus

Analysis cont’d, the repair

So the input bulk cap in the DPSN-130AB had visibly failed and was clearly bad, and it was replaced by a KXJ 120/450. As it is 1 cm taller than the original, I had to add some insulation on its top to seperate it electrically from the chassis.


But as you can see, that alone wasn’t enough to fix it, as more of the capacitors needed to be changed. I went ahead and also tested the small capacitors on the primary side, around the hot components. As I expected, most of them had already failed. Though Delta used parts from the higher-quality series capacitors that were available back in 2005, most of them still failed after such a long time in such a harsh environment.


Nippon chemi-Con, Panasonic, Rubycon, they all failed. These small caps have been replaced mostly by low-ESR capacitors from some of the more modern series that I stock (KYA, KZM, KZN). A few weeks back I also started stocking the LE series which have a claimed 10000 hour endurance rating, and I’ll use these to gradually replace some of the other stocked low-ESR series in the future.


The source of most of the heat was two resistors that were connected in series, acting as current sensors on the primary side. Because of excessive switching caused by the bulk capacitor failing, they produced even more heat than usual. When I desoldered them, the trace connecting them just fell right off the board.


So I soldered them together, leaving them just “floating” so-to-speak (also referred to as the “flying resistor mod”). In this case no extra insulation was necessary as these have a kind of thick and rigid metal lead. Thanks to that they stay in the position you put them in more or less forever. After reassembling both the DPSN-130AB power supply and the DesignJet 110plus printer together, the printer fired right up and has already been in service for a year now.


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