[unwind]

The core analysis seems to be:

> A common issue with these types of components is that the quiescent current which ensures for the internal circuitry to work properly depends on the ambient temperature. If it’s too low and the regular doesn’t have enough supply current left the output appears to be dead.

Which honestly makes very little sense to me, and also reads a bit like a terminology tombola. A quick googling did not turn up more material on the idea that voltage regulators depend on the temperature like that, and it would be surprising (generally electronics performs better when cooled).

I would expect the problem to be due to a bad solder joint, which would explain why heating it helps since it might make the solder flow a little bit back into making connection (although hair dryer temperatures at 200°F/93°C) are too low to properly reflow solder). Or it might just make components and/or solder expand enough to make contact (which is kind of the same thing but different).

All real hardware experts, please explain. :)

[Gordonjcp]

In the olden days we used to use hair driers and cans of "freezer spray" - ozone-depleting freon in a can, now replaced with more eco-friendly stuff - to heat and cool components to see which ones were temperature-sensitive. Quite often you'd get a fault that would only show up when the set was cold, or only after it was thoroughly warm.

I'm wondering if perhaps C206/C207/C208 in the LDO circuit that decouple the output might have gone a bit leaky and warming them up causes them to act more like capacitors and less like resistors to ground. If they're SMD multilayer ceramics that would be a pretty common failure.

[_Microft]

The part is a LDO (low-dropout regulator). You can read about these here. See also the section about the quiescent current. One more thing: what made you believe that the given explanation is wrong?

https://en.wikipedia.org/wiki/Low-dropout_regulator

https://en.wikipedia.org/wiki/Low-dropout_regulator#Quiescen...

[avianlyric]

> quiescent current which ensures for the internal circuitry to work properly depends on the ambient temperature.

This statement seems to get the relationship between quiescent current and the operation of internal circuitry backwards.

Quiescent current doesn’t power the internal circuitry. Quiescent current is a measure of current consumed by the internal circuitry while it’s idle.

The temperature relationship exists because the circuitry consumes more power when it hot. But there isn’t some temperature dependent magically quiescent current provider that must work correctly for the rest of circuitry to operate. Just like there isn’t a “standby power provider” inside of a TV to allow it to remain in standby. The standby power is just a measure of the power consumed while in standby.

[unwind]

I really do understand what LDO means, and at least a decent amount of how they work.

I still don't think it makes sense; it's not as if you have the heat the device to be hot enough to draw the quiescent current, it's the other way around. As the internal temperature rises, the efficiency of the components degrade, things start to "leak" more current and the quiescent current draw goes up.

[tgsovlerkhgsel]

I think it makes sense when you read it carefully. What tripped me up is that quiescent current is usually only seen as a bad thing. It not drawing enough current also seems more like a symptom than the cause.

On my first pass I was also a bit confused whether he is talking about the regulator's internal circuitry or something else: It's not obvious that LDO stands for low-dropout regulator, so at first it felt like he's misusing "quiescent current" to refer to some kind of "standby current" (comparable to an ATX power supply +5V Standby line) that the regulator has to supply to some other circuitry that then powers on the regulator to supply the rest of the device.

[ariejan]

It's not uncommon for solder joints to get damaged due to heat stress. It happens to BGA compontents too when not properly cooled. The hair dryer may or may not have provided enough heat to fix a small crack (I didn't look up the temperature a hair dryer provides).

Did kind-of the same with my Philips TV a while back. Still going strong.

https://www.devroom.io/projects/repair-philips-42pfl6057h-12...

[cestith]

"Hair dryer" is such an imprecise term in a use case like this. One can find 600 watt units all the way through about 2300 watts. A typical general-purpose heat gun one might use to strip paint or shrink some heat-shrink plastic is usually between 1500 watts and 1800 watts.

[mannykannot]

While the power consumption may vary considerably, the maximum temperature is presumably constrained by what humans and their hair can tolerate.

[londons_explore]

Put a thermocouple in some hairdriers and you'll find some get well over 400 Celcius (750F!).

They just rely on the fact air has a low thermal mass, and it's easy to just keep it slightly further from your skin if necessary - the air quickly cools with distance as more room air mixes in.

[cestith]

There is a huge difference in whether one can actually reach that temperature, how quickly, and how much airflow it provides across the heating element and on target. A heat gun is a much more consistent tool for the uses for which it's designed.

[bombcar]

A heat gun is also designed to put pretty consistent heat an inch or so away from the nozzle, whereas hair dryers often have what appear to be left-over jet engines for fans, for when you need to dry someone's hair from ten feet away.

[pie314isi]

I agree, it makes no sense. I am a real hardware electronics engineer and I don't understand his explanation. I believe the LDO could fail in a temperature dependent way. I do not believe the explanation.

[jonsen]

> ...a bad solder joint

Or inside the IC a bad bonding between the chip and the package leads. Or IC package developed cracks and moisture creeps in.

[type0]

> Or it might just make components and/or solder expand enough to make contact (which is kind of the same thing but different).

Yeah, most probably it deformed into contact

[laci37]

I am not an expert, just a hobbyist. It's hard to tell anything without measurements. Either the regulators are half dead (factory spec for operating temperature is -40 to +85 C°) and should be replaced, or thermal expansion causes a cracked solder joint to touch again, or some other component is half dead and needs a bit of warmth to work properly.

[ivanbakel]

>A quick googling did not turn up more material on the idea that voltage regulators depend on the temperature like that, and it would be surprising (generally electronics performs better when cooled).

Not a hardware expert either, but Wikipedia points at this TI doc[0] which claims ambient temperature is necessary for the quiescent current. There's no mechanism described there, though.

[0]: https://www.ti.com/lit/an/slva079/slva079.pdf

[formerly_proven]

These have ground pins (as opposed to floating regulators), so they draw whatever bias current they need (which mostly depends on temperature, input voltage, output current and the lottery). The explanation is bogus, and doesn't explain how heating once would help with a problem caused by too low ambient temperature during operation anyway.

[jonsen]

> ambient temperature is necessary for the quiescent current

No it does not say that. It says ambient temperature is a factor contributing to quiescent current:

"The value of quiescent current is mostly determined by the series pass element, topologies, ambient temperature, etc."

In an LDO you normally want as little as possible quiescent current when idle. You certainly wouldn't design stand by operation to be dependent on temperature. If it turns out to be so with time, it's an aging problem.

[thomasthorpe]

Old thread now. But often a minimum load is needed for an LDO, particularly on older parts, to work correctly. Such that these are given in datasheets. This is continuously required so is effectively quiescent current. I think this is what the OP was trying to get at.

But failed capacitor reulting in instability seems much more likely.

[jonsen]

You are right that a small quiescent current is necessary for correct idle operation. But much of the discussion here is about the misconception that a certain ambient temperature is necessary for correct operation by design.

By the way it is in fact imaginable that aging has caused the quiescent current to become too small at low temperature.

There are several possible temperature dependent fault mechanisms caused by aging, so I wouldn't make a guess in this case.

[audiometry]

What is a “terminology tombola”. All I can find is tombola is some kind of lottery.

[unwind]

Yes, to me the text read as if the author put some relevant words into a rotating drum and then picked them out. The result is a random-seeming sentence, which is my attempt at explaining how it read, to me. I was not aiming for snark, apologies if that's how it came across.

[zerocrates]

"Word salad"

[cestith]

It's similar to "buzzword bingo".