I have a non-working power amp Crown xls 1000 that is dead. Checking just past the power supply there is a shorted-out PTC thermistor reads on the face PTC-840-1011, it's a 6-ohm thermistor.
This part is no longer made but here is the replacement according to digikey... https://www.digikey.nl/nl/products/detail/amphenol-advanced-sensors/YQD120N0006/2324592
My question is and probably a dumb question, for testing purposes, can this PTC thermistor be bypassed with a resistor or with any other PTC thermistor of similar readings?
This is my first time dealing with a thermistor.
Thanks in advance
This part is no longer made but here is the replacement according to digikey... https://www.digikey.nl/nl/products/detail/amphenol-advanced-sensors/YQD120N0006/2324592
My question is and probably a dumb question, for testing purposes, can this PTC thermistor be bypassed with a resistor or with any other PTC thermistor of similar readings?
This is my first time dealing with a thermistor.
Thanks in advance
Use a dim bulb tester, those don't fail often, must have been big fault.
They are there to control inrush current, so there must be a short circuit.
Dead amp = big clue.
Check primary side, before replacing.
If okay, yes, can substitute, common in refrigerators for example.
See above again, failure means catastrophic failure in the unit.
They are there to control inrush current, so there must be a short circuit.
Dead amp = big clue.
Check primary side, before replacing.
If okay, yes, can substitute, common in refrigerators for example.
See above again, failure means catastrophic failure in the unit.
Can these thermistors just fail occasionally on their own? BTW the dim bulb tester is a great idea.
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Thermistors can fail in service.
When you say
then if it is 'shorted' either by being linked out by somebody or if it reads 'short' in circuit then the amp should power up. It would have to be open to stop the amp working.
When you say
then if it is 'shorted' either by being linked out by somebody or if it reads 'short' in circuit then the amp should power up. It would have to be open to stop the amp working.
Thank you for your reply. The thermistor would heat up right away, to the point where it would smell burning just having it on for a few seconds. It reads short removed from the circuit and yes, if it were open, it would be as if it were removed from the circuit. The part is just before the "soft start" relay.
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Then you have a GROSS short downstream. you´ll have to find and deal with it.
Is the Thermistor really shorted?
I´m not so sure, since it seems to be doing its work, and by definition a short does not heat up, so ....
I guess you are measuring it in-circuit.
And yes, a dim bulb tester is a great idea to start with.
Get the schematic and post it here for useful answers.
Is the Thermistor really shorted?
I´m not so sure, since it seems to be doing its work, and by definition a short does not heat up, so ....
I guess you are measuring it in-circuit.
And yes, a dim bulb tester is a great idea to start with.
Get the schematic and post it here for useful answers.
I just looked at the schematic... this is not quite what I expected tbh its not diy friendly unfortunately.
This is a complex uP controlled amp with smps and Class D output stages. Fault finding is going to be complex and involved and would need a very methodical approach to see whether the power supply is OK and the problem elsewhere or whether it is purely a power supply fault. Much of the power supply is live at all times which is a real safety issue unless you are familiar with correct working practice for these.
This is a complex uP controlled amp with smps and Class D output stages. Fault finding is going to be complex and involved and would need a very methodical approach to see whether the power supply is OK and the problem elsewhere or whether it is purely a power supply fault. Much of the power supply is live at all times which is a real safety issue unless you are familiar with correct working practice for these.
Agree this is not a beginner repair.
I assume we're talking about RT901 in the drawing, yes? The relay contacts short it out after inrush so it doesn't impede current delivery.
So, if it gets hot and stays hot then the relay is never shorting it out. Does the relay click a few seconds after power-on? If yes, you might have burned contacts in the relay itself.
And to be clear, downstream of any burned contacts you're likely to find the real problem. Again, not a rookie job, this one...
I assume we're talking about RT901 in the drawing, yes? The relay contacts short it out after inrush so it doesn't impede current delivery.
So, if it gets hot and stays hot then the relay is never shorting it out. Does the relay click a few seconds after power-on? If yes, you might have burned contacts in the relay itself.
And to be clear, downstream of any burned contacts you're likely to find the real problem. Again, not a rookie job, this one...
PTC is Positive Temperature Coefficient, meaning the resistance increases to open very fast after supply is given.
Common in A/c compressor circuits, a replacement for the relay type circuits.
Failure rates are low, it is considered a reliable part. Of course, occasional failures do happen, but most likely fault is in the rest of the circuit.
My suggestion is to find a service manual, decide if your skills are good enough, and proceed with extreme caution.
Get an estimate if needed.
Some parts get degraded after a big jolt, so the remaining life of the unit is badly affected. It may not be worth the trouble.
Or buy another amp, may be less expensive.
Or, of course, BUILD one, this is a DIY site!
Common in A/c compressor circuits, a replacement for the relay type circuits.
Failure rates are low, it is considered a reliable part. Of course, occasional failures do happen, but most likely fault is in the rest of the circuit.
My suggestion is to find a service manual, decide if your skills are good enough, and proceed with extreme caution.
Get an estimate if needed.
Some parts get degraded after a big jolt, so the remaining life of the unit is badly affected. It may not be worth the trouble.
Or buy another amp, may be less expensive.
Or, of course, BUILD one, this is a DIY site!
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I am measuring it (the thermistor RT901) removed from the board, and what is "is it really shorted" means? Isn't a thermistor supposed to have a reading and also vary with temperature or is it just supposed to read 0 ohms throughout?
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Thanks for the advice. Yes it is RT901, gets hot to the point that you can smell it, removed from the circuit it's shorted. Turning on the amp, no clicks, no fan, nothing. Not a beginner but definitely no expert, which is the reason I'm posting here. The amp didn't cost me anything, I took it as a project but definitely over my head, nothing like working on the older amps.
From a practical point when you talk of 0 ohms (which nothing ever is that we on here deal with, not even a piece of wire) you need to be sure you are using a meter capable of resolving low ohms. A 100 ohm or 1000 ohm resistor can appear to read 'short' on a meter set to an inappropriate range.
For a typical meter if you short your meter leads together you should see a reading of between 0.1 to around 0.3 ohms depending on how thick the leads are. Lets say you get 0.3 ohm. That is as low a reading as you can get on that meter. If you then measure a resistor and it reads 0.7 ohm then the real resistor is actually 0.4 ohm (which is 0.7 minus the constant 0.3 ohm lead resistance).
For a typical meter if you short your meter leads together you should see a reading of between 0.1 to around 0.3 ohms depending on how thick the leads are. Lets say you get 0.3 ohm. That is as low a reading as you can get on that meter. If you then measure a resistor and it reads 0.7 ohm then the real resistor is actually 0.4 ohm (which is 0.7 minus the constant 0.3 ohm lead resistance).
Cold PTC always conducts, you think it is shorted.
Its resistance should go up to open in the time it takes a compressor to start up, less than half a second, that happens on load, not out of circuit.
Some may have different time constants, but I feel 5 seconds is maximum, could be wrong.
If it is not doing so, you are in big trouble.
Read the articles above, think things over, then proceed.
And yes, always zero the meter, or check the shorted leads reading.
Make sure batteries are good.
Its resistance should go up to open in the time it takes a compressor to start up, less than half a second, that happens on load, not out of circuit.
Some may have different time constants, but I feel 5 seconds is maximum, could be wrong.
If it is not doing so, you are in big trouble.
Read the articles above, think things over, then proceed.
And yes, always zero the meter, or check the shorted leads reading.
Make sure batteries are good.
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Thanks again. I believe a thermistor should show a reading other than short and vary with temperature?
NTC and PTC are almost opposite in working characteristics, read the articles to clear your doubts.
Then come back with a clearer concept.
Your queries will be answered, within reason of course.
Then come back with a clearer concept.
Your queries will be answered, within reason of course.
It checks "short" on leads reading. It is a PTC here is the link for it...
https://www.digikey.nl/nl/products/detail/amphenol-advanced-sensors/YQD120N0006/2324592
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I said that already!
"Cold PTC always conducts, you think it is shorted.
Its resistance should go up to open in the time it takes a compressor to start up, less than half a second, that happens on load, not out of circuit."
It seems okay, but you have to check in circuit, on load.
That is another issue, given its short time constant. testing is not easy.
Because it has been heated to smelling, I would consider it unreliable, and replace it.
I said that already!
"Cold PTC always conducts, you think it is shorted.
Its resistance should go up to open in the time it takes a compressor to start up, less than half a second, that happens on load, not out of circuit."
It seems okay, but you have to check in circuit, on load.
That is another issue, given its short time constant. testing is not easy.
Because it has been heated to smelling, I would consider it unreliable, and replace it.
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So even putting it next to a heat source while connected to the multimeter, should it still read short?