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missing SMD component

I had a bench power supply finally act weird, which I only noticed when playing with one of the UV LEDs, which even radio shacks sells now.

At one point, when in CC mode, the LED started to flicker and the power supply made a weird clicking sound.

Outside of CC mode, the output looked OK. The B output (dual output unit) worked fine.

The maker, TTI in the UK kindly supplied the service manual which I wanted for the recalibration steps.

It turns out one of the internal -5v regulators (just a zener) for powering the front control panel was completely missing. I had no idea it belonged there as the board looked pretty clean with nice solder fillets on the 3 pads where the sot-23 zener belonged. Super close inspection showed there may have been glue/flux/something where the body of the diode was.

I guess it never wetted correctly at the factory and then 5 years later FINALLY fell off.

So the lesson is two fold

- check the power supplies inside broken power supplies

- maybe missing parts weren't options or ECs.

If anybody in the US has a spare BZX84C5V1 5.1V 350mW sot-23 zener they can drop in an envelope, I'll send a few bucks your way. drop munge from my email address.

Reply to
Cydrome Leader
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I suspect it is more likely it went short circuit and melted itself off.

Gareth.

Reply to
Gareth Magennis

One of the three leads had no electrical connection, but had a solder pad, with just a nice lump of solder.

The energy in that section is pretty low, but who knows, maybe it did melt and fly away.

Reply to
Cydrome Leader

You can get 'em off ebay dirt cheap free shipping. I bought some, but they were SOD-323. Is the board spacing so close you can't cobble in a leaded part and be done with it? Insistence on the correct part is overrated ;-)

Reply to
mike

The 2 connection zener was in a 3 connection package, quite common with SMD diodes.

The zener would have had a series resistor on the PCB limiting the current, possibly just enough to desolder it, without causing any other damage or evidence that this actually happened.

Gareth.

Reply to
Gareth Magennis

It does not take much of a jar to loosen a SMD that was only marginally held in the first place. As unlikely it will get jarred now on the bench, I would wire in a conventional zener , perhaps with a sub-mm drill hole through the pcb, if concerned about structural integrity

Reply to
N_Cook

It would actually be more work to take the PCB out of the chassis to do a weird retrofit, although there's plenty of space.

Reply to
Cydrome Leader

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