Princeton Tec Quad problems?

I’ve seen this phenonmenon before in other headlamps and over the years with some other electronic equipment.

In this case, my semi-educated guess is that there is a high-resistance path allowing a small amount of current to flow.

Since i am unfamiliar with the actual circuitry used in the Quad (i.e., i’ve never seen an electronic schematic diagram of the Quad’s circuitry), i can’t be sure of the cause of this high resistance path.

However, based on my approximately 45 years of experience building, troubleshooting, and repairing electronic equipment, here is my semi-educated guess:

1. If the on/off switch is not designed to be part of a digital control/switching circuit (meaning that actual lighting current flows through the switch), then on/off switch is NOT fully breaking contact. In other equipment in the past i’ve corrected this problem by “using a bigger hammer”. What i mean is more forcefully, cycle the switch with your finger (not a hammer) 10, 20, 50 times and see if that corrects the problem. Use your finger more forcefully; don’t use a hammer.

If the switch is just applying control voltage to an IC (integrated circuit) that then handles the control of the headlamp and in turn turns on a high-current device to supply current to the LEDs, then this corrective action probably won’t work.

2. There is a high resistance path elsewhere due to either poor manufacturing, or the thing has “ingested” some water, or another electolytic fluid (soda pop is a good conductor), and needs to dry out – place it in an oven at 110 deg F for a few hours to a few days – AFTER removing the batteries.

Last year, i disassembled a no-name 5x5mm white LED cap-brim light i bought from REI and found a cracked circuit board. Not sure you can disassemble the Quad sufficiently without damaging it to get to the electronics. If you do attempt it, and find a cracked circuit board or a cold solder joint, then try the following using a low wattage soldering iron (NO MORE than 27watts) with a very fine tip.

If a cold solder joint, reheat the joint and if necessary apply just a bit more solder (“less is more” in this case).

If a cracked circuit board, either find lands or circuit board pass-throughs that are electrically the same point. To do this: a) visually inspect the board to locate likely areas, and then b) use a mult-meter set in either resistance or continuity mode to positively determine that the points are electrically the same. Then, if necessary scrape any insulating layer off of the circuit board trace (unless a land or pass-through is to be used, then there is probably no need to scrape), and “tin” the surface of the land, pass-through, or cleaned trace (DO this quickly to minimize the application of heat to the circuit board – too much heat can “fry” the little chips). Using a #26 gauge or finer wire, “bridge” the open/intermittent connection in the cracked circuit board. If necessry (it probably won’t be as there is not a lot of metal around to cause a short-circuit with the repaired area), re-insulate the area using clear finger-nail polish, or another subtance (super-glue), or a bit of electrical tape.

I’ve actually seen cracked Li coin cell holders (which also function as the “battery-box” terminals cause this problem also. In this case, just use some solder to repair the battery holder/terminals. It’s a low stress/cycle area and over time shouldn’t fatigue the solder “bridge”.

3. One of the electronic semi-conductor components is in a “failure” mode and is partially shorted internal to the device, allowing a small amount of current to flow – over time, and as it heats up under full power operation, it may fully “short” and burn-up (i.e., become an “open” circuit). I, personally, wouldn’t attempt repair in this case – not haveing a schematic diagram nor a bin of spare parts. In actuality, the entire cirucit board is probably a LRU – line replaceable unit – an is replaced and thrown away – even by Princeton Tec technicians no repair is probably attempted – parts are cheap; labor troubleshooting and repairing isn’t.

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If it’s convenient to do so, you might just want to get the defective unit exchanged. I have a PT Quad – it is a fine headlamp. You’ll probably be very pleased with it once it’s repaired or you get a properly functioning unit.

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Note: FWIW, electronic components themselves (i.e. semi-conductor devices) generally have two main normal “death” modes (not an electrostatic discharge or some other mis-use related demise):

a) “infant mortality” which is often defined as the first 168 hours of operating life (not shelf-life). This typically comes about by poor manufacturing of the “chips”/components by having humid air in the “clean room” (a problem for tropical environment where so many electronic components are mass produced for the last 20 or so years). The incorporation of moisture into the device, ends up reacting, in the presence of electricity to form acid which destroys the device from within.

b) “old age” is the second main normal “death” mode. The friction of electrons flowing through a semi-conductor device and the heat produced eventually takes its toll and the device dies (typically tens of thousands of hours later – less in very high-current applications since more “trons” are flowing and more heat is produced. Heat is anathema to semi-conductor devices. Silicon junctions break down at ~175 deg C internal temperature. This can, in some designs, be acheived by an internal air temperature inside of the “box” or “cabinet” of even just 95deg F [these numbers are from actual experiments i conducted on some of our equipment ~27 years ago).

Thanks for your thorough dissertation Paul.

One other symptom with the unit is when the last battery is placed (completing the circuit but without the switch) in the unit the LED’s flicker once on high for an instant. Does that narrow the problem down?

Hi John,

I second Paul’s recommendation to utilize PT’s lifetime warranty. I’m testing the Quad, and it exhibits none of the behaviors you’re describing.

Good luck.

John,

I’ve seen this “flicker once” happen on some other devices as part of a normal, simple, partial self-test (self-check) mode upon battery insertion. Not sure if that’s what’s happening with the Quad.

Sorry, i can’t be more help.

I sent it back to the dealer this morning. Unfortunately I don’t have the tools to correctly diagnose the problem otherwise I could’ve been an interesting study of current regulation circuitry and component outsourcing/ quality.