rewindhifi Posted November 9, 2023 Posted November 9, 2023 Hello All, I am trying to identify a faulty transistor part no but there is this component glued to it, was connected between pin B-E of the transistor Anyone know what is it? some kind of thermal sensor? Thank you so much for your time!
bob_m_54 Posted November 9, 2023 Posted November 9, 2023 It could be a thermistor. What is the equipment? 1
rewindhifi Posted November 9, 2023 Author Posted November 9, 2023 Its from a power amp, yes I think its some sort of temperature sensor but I want to ensure that I can find a replacement before removing it from the transistor. I think the transistor look like a a Motorola F15030 but not confidence
bob_m_54 Posted November 10, 2023 Posted November 10, 2023 7 hours ago, rewindhifi said: Its from a power amp, yes I think its some sort of temperature sensor but I want to ensure that I can find a replacement before removing it from the transistor. I think the transistor look like a a Motorola F15030 but not confidence Make and model of the equipment will get you more useful information..
bob_m_54 Posted November 10, 2023 Posted November 10, 2023 2 hours ago, Addicted to music said: Thermistor or a temp poly switch Polyswitches are over current devices.
Addicted to music Posted November 10, 2023 Posted November 10, 2023 59 minutes ago, bob_m_54 said: Polyswitches are over current devices. resettable fuses, you can get them with certain PTC: positive temp coefficient, where it trips to high resistance when temp is exceeded. So in this case if it’s mounted on a device it can trip for overcurrent or high temp.
bob_m_54 Posted November 10, 2023 Posted November 10, 2023 Just now, Addicted to music said: resettable fuses, you can get them with certain PTC: positive temp coefficient, where it trips to high resistance when temp is exceeded. So in this case if it’s mounted on a device it can trip for overcurrent or high temp. No, polyswitches or PTC fuses are tripped due to over current. Over current through the device causes it to heat up and go high resistance. Thermistors activate by temperature. When the temperature of the device is increased by external causes, the temp increases for PTC or decreases for NTC. https://www.youtube.com/shorts/8NdTu5koaEY
Addicted to music Posted November 11, 2023 Posted November 11, 2023 1 hour ago, bob_m_54 said: No, polyswitches or PTC fuses are tripped due to over current. Over current through the device causes it to heat up and go high resistance. Thermistors activate by temperature. When the temperature of the device is increased by external causes, the temp increases for PTC or decreases for NTC. https://www.youtube.com/shorts/8NdTu5koaEY So what’s wrong with what I said? the utube video is exactly the behaviour what I have stated: 1 hour ago, Addicted to music said: resettable fuses, you can get them with certain PTC: positive temp coefficient, where it trips to high resistance when temp is exceeded. So in this case if it’s mounted on a device it can trip for overcurrent or high temp.
bob_m_54 Posted November 11, 2023 Posted November 11, 2023 (edited) 12 minutes ago, Addicted to music said: So what’s wrong with what I said? the utube video is exactly the behaviour what I have stated: OK, similar in the way they act, except the polyswitch is used in series with the current flow and will go high resistance when current through it is exceeded, and interrupt the current flow. As thermistor senses heat, and can either be NTC or PTC and changes resistance with changes in sensed heat. I'd hazard a guess the device is a NTC Thermistor, and is used as a bias control/regulator for the transistor. Edit: it would help if the OP would post the Make and Model No of the amp though.. Edited November 11, 2023 by bob_m_54 more
Addicted to music Posted November 11, 2023 Posted November 11, 2023 the reason I state it maybe a poly switch is because thermistors on there own are usually a dollop or round ball with 2 connections hanging of it, this has a circular plate! Never seen thermistors looking like this, resettable fuse are popular due to their sizes, the issue is once they set, it usually means something else is wrong and needs attention.
rewindhifi Posted November 11, 2023 Author Posted November 11, 2023 Thanks both, very interesting conversations Silly me, its from an old Conrad Johnson SA-400, no luck finding the service manual. I done some measurement and the initial resistance was around 800R after applying some heat the resistance decreases as its temperature increases Is this a negative temperature coefficients thermistor? by the way its was connected between the base and emitter pins 1
bob_m_54 Posted November 11, 2023 Posted November 11, 2023 8 hours ago, Addicted to music said: the reason I state it maybe a poly switch is because thermistors on there own are usually a dollop or round ball with 2 connections hanging of it, this has a circular plate! Never seen thermistors looking like this, resettable fuse are popular due to their sizes, the issue is once they set, it usually means something else is wrong and needs attention. The blob types are common, but there are all different shapes. https://www.sensorsci.com/thermistor-resistance-and-bias-current
bob_m_54 Posted November 11, 2023 Posted November 11, 2023 47 minutes ago, rewindhifi said: Thanks both, very interesting conversations Silly me, its from an old Conrad Johnson SA-400, no luck finding the service manual. I done some measurement and the initial resistance was around 800R after applying some heat the resistance decreases as its temperature increases Is this a negative temperature coefficients thermistor? by the way its was connected between the base and emitter pins Yes it is a NTC Thermistor, of the resistance drops when you heat it. A PTC would do the opposite,
Addicted to music Posted November 11, 2023 Posted November 11, 2023 12 hours ago, bob_m_54 said: The blob types are common, but there are all different shapes. https://www.sensorsci.com/thermistor-resistance-and-bias-current Here’s a real NTC contact sensor thermistor…. There’s contactless inferred types we used too, but it’s the contact ones that fail.
Addicted to music Posted November 11, 2023 Posted November 11, 2023 Because it’s connected the the base and emitter, I’m guessing it’s there to reduced the bias as it heats up. 1 1
bob_m_54 Posted November 12, 2023 Posted November 12, 2023 9 hours ago, Addicted to music said: Because it’s connected the the base and emitter, I’m guessing it’s there to reduced the bias as it heats up. Didn't I say that??? 1
rewindhifi Posted November 12, 2023 Author Posted November 12, 2023 Got it removed What do you recommend a good replacement? Do you reckon these can work? https://au.mouser.com/ProductDetail/Vishay-BC-Components/NTCLE100E3681JB0A?qs=vLWxofP3U2wqaJ7guKdRLg%3D%3D https://au.mouser.com/c/circuit-protection/thermistors/ntc-thermistors/?resistance=800 Ohms Many thanks.
bob_m_54 Posted November 12, 2023 Posted November 12, 2023 Wasn't there a number on the other side of the Thermistor?
bob_m_54 Posted November 12, 2023 Posted November 12, 2023 10 hours ago, Addicted to music said: Here’s a real NTC contact sensor thermistor…. There’s contactless inferred types we used too, but it’s the contact ones that fail. yes, that's one type of thermistor...
bob_m_54 Posted November 12, 2023 Posted November 12, 2023 6 hours ago, rewindhifi said: No marking on both sides. Brown Black Red = 1Kohm. As they are usually quoted at 25deg C (room temp) then your 800ohm at 30C would correlate. https://au.element14.com/amphenol-advanced-sensors/rl2004-582-97-d1/ntc-thermistor-1k-radial-leaded/dp/2847963
Addicted to music Posted November 12, 2023 Posted November 12, 2023 (edited) If your applying heat and the temp drops due to its NTC characteristics, then that thermistors is working…..nothing wrong with it. Usually when they don’t work it’s open circuit. Very rare do you see short circuit to indicate a fault code, and if we encounter short circuit codes it’s usually the thermistors has been knocked out of position and the section is trying to heat up! it’s usually open circuit…. I would not even think about replacing that, especially if you physically tap on on it as a vibration test and the values doesn’t fluctuate …. If it tick these boxes, leave it alone….especially if you don’t have a circuit diagram or precise info at hand. Edited: it’s not even in extreme temps: > 150C… the pic of the one I use that measures from room temp to 250C. We know when that’s faulty, it’ll give you false SC codes that a tech has to reset. Edited November 13, 2023 by Addicted to music 1
bob_m_54 Posted November 13, 2023 Posted November 13, 2023 @Addicted to music yes I agree, if they are not physically damaged from the removal process, and they both measure the same (+/- 5%), throughout a series of readings, say 25degC to 65degC, then they should still be OK.
Addicted to music Posted November 13, 2023 Posted November 13, 2023 8 hours ago, bob_m_54 said: @Addicted to music yes I agree, if they are not physically damaged from the removal process, and they both measure the same (+/- 5%), throughout a series of readings, say 25degC to 65degC, then they should still be OK. usually when you have heating problems it’s not becuase of the thermistor, it’s the components you’re monitoring that’s the issue…. Usually! .
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