I bought my Canon iP4200 printer around 2007-08, a replacement for another Canon, the BJC-80 model. The BJC is still in a box somewhere, sans a working print-head. Its two main issues when working, were both head-related;
Enter the iP4200. This was streets ahead of the BJC in almost every respect. Its resolution was fantastic for the time, and super-cheap ink-refills were readily available from the get-go - what wasn't there to like!
My brother had earlier bought the same model and had introduced me to it when it would no longer turn on. The fix proved quick & simple - a rectifier diode in the slot-in PSU module (a nice feature, I thought at the time!) had failed.
Brief as this introduction to the iP4200 was, it was all the incentive needed for me to fork out for the same model when the BJC finally gave up the ghost. It's been 16 years since the purchase, and I've never had a problem with it. The print-head is still the original one, with no bad/blocked nozzles. Yes, one excellent printer - until a few days ago anyway!
After sitting unused for several months, when switched on, I found that the middle button's yellow light would flash eleven times, in a cyclical manner, and little else. It turned out that according to Canon, this signified Error 5110: a 'Carriage Lift Mechanism Error'. Fault-codes aside, there seems to be a real dearth of repair information for any Canon printer available online, never mind the stodgy old iP4200. That, or 'Google Search' continues to deteriorate. [Note: after the fact/repair, I found that an actual service manual exists for the iP4200, which appears quite instructive, and which I'll link to here].
So, with no pointers to get me started, I opted for just opening it up and having a look around. Alas, nothing obvious seemed amiss. So there it lay for a day, its innards exposed to all & sundry. And the Sun! In this environment, I accidentally discovered that when exposed to bright sunshine, the printer would work normally! Long story short, I soon tracked down the faulty component, the 'Carriage Lift Sensor' (CN401). Composed of both a light-source & light-detector, only the source-part had failed - and the reason, that with sufficient sunshine present, the light-detector side would trigger normally! After fruitlessly searching online for a vendor of what was probably a long-obsolete part, rather than junk an otherwise perfectly good printer, I resolved to 'MacGyver' a solution if at all possible.
Since I presumed that the employed light-source in question, was infrared, I figured the light-detector would be similarly oriented - a problem, as I possessed no IR LEDs of any description. Testing with what I had available, namely, Red, Green, Yellow & White LEDs, I was elated to discover that pretty much any type would trigger the light-detector. The only real considerations were that of, size, (very limited space is available), and power-limiting, (enough to trigger, but not to tax the original supply circuitry). While the White LEDs seemed the most efficient, its 'size' excluded it from consideration, so limited my options to Red, Green or Yellow LEDs. Surprisingly, the Red light triggered the most reliably, while drawing the least current - a paltry 1-2mA, using a 1k current limiting resistor.
As can probably be seen from the photos, the LED is positioned alongside the original sensor and must be 'aimed' at the light-detector on the other side in order to effect the greatest illumination possible.
