Re: LM317T Voltage Regulator Input Resistor Cremation.
Problem now resolved, the capacitor between the adjust pin and GND was reverse polarity.
Darky8
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Last Activity: 12-18-2022, 10:36 AM
Joined: 07-13-2013
Location: Kent
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Re: LM317T Voltage Regulator Input Resistor Cremation.
Sorry, but I'm struggling to make this any clearer. I was attempting to highlight the different ways in which each regulator responded, the working one compared to the non-working one. (oh and by low, I meant comparatively, ~1.85M)...Last edited by Darky8; 10-15-2016, 12:36 AM.Leave a comment:
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Re: LM317T Voltage Regulator Input Resistor Cremation.
The LM317 is the one that burns the resistor....Leave a comment:
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Re: LM317T Voltage Regulator Input Resistor Cremation.
Hi, Sorry I missed the input pin test.
I tested the LM377 (the working one) and got 1.39-1.44M/ohms stable at input pin.
I tested the LM317 input pin and started at a low reading, but grew rapidly until I removed my meter at around 22M.
I also found that the TAN across the input was charged to 0.38v, the others had no charge.
The 3 6.8pf 35v caps measured
6.66pf 0.76 ESR
6.48pf 0.60 ESR
6.52pf 0.22 ESR
Could I swap these for 10uf 50v just...Leave a comment:
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Re: LM317T Voltage Regulator Input Resistor Cremation.
If I remove them, I don't need to power the circuit. I can simply measure the resistance between the Ouput and GND, then put them back afterwards.
I can't see it being a problem on the output side. I've pretty much isolated it and it still melts resistors.
We'll see what it does with some new caps.Leave a comment:
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Re: LM317T Voltage Regulator Input Resistor Cremation.
Actually I know where that resistance is coming from.
It's the two resistors for the adjust! DOH.
I would have to remove them, then measure the output pin....Leave a comment:
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Re: LM317T Voltage Regulator Input Resistor Cremation.
Yeah, I'm going to try and get everything disconnected from the output to see if it works then.
If it does (which I doubt it will), we'll pop them back in one by one and see.
I might also knock up a quick off-board LM317 circuit, and try and power things with that.Leave a comment:
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Re: LM317T Voltage Regulator Input Resistor Cremation.
Hi, folks!
Sorry this has been a bit of a long time coming. But I enclose some much better pics.
The LM317/LM337 combo supply +/-22~v to the two ceramic output PCB's. Pins 1 & 2 -22v, GND, then 4 & 5 +22v.
The +33 and -33v are fed to only these two regulators, all the rest are running lower voltage and outputting ~5v.
The lone 337 works fine (as do all the rest of the other 317's) with stable negative output.
I have removed both ceramic line boards, and...Leave a comment:
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Re: LM317T Voltage Regulator Input Resistor Cremation.
Hi, I did check the resistance on the output pin. And it's 3.8k to GND.Leave a comment:
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I'm a IT engineer fed up with plugging shiny boxes into each other! Loosing what ever brain cells I had left, and working with demented folk you lost theirs years ago.
I'm great with electrics, and specialize in cable making. But I really want to get right into the detail of what makes electronics work. Nothing mad, just to be able to fix simple things. And a deep desire to know what makes things tick.
Unlike many others I'm Autistic (Attention to detail ++, OCD +), I won't pretend to know anything I don't. I know what I'm good at and what I'm not, and I leave it there.... -
Re: LM317T Voltage Regulator Input Resistor Cremation.
Firstly sorry I can't get any more pictures ATM, not at home.
It's the LM317 that's frying the resistor, the LM337 works fine as do 3 other LM317's (But they are around 12v feed, with 5v output).
So there are two transformers and 3 1000uf 35v caps, nothing else in the power supply at all.
however, these solid caps don't sit with me at all well. The unit has had questionable repairs/soldering, plus it's an 1990's DAC. So I de-soldered all the caps in order to clean up the board, and solder...Leave a comment:
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Re: LM317T Voltage Regulator Input Resistor Cremation.
Thank you.
It's from a hifi DAC.
The 317 works along side a 337 to drop +/-33v to +/-22.5 (sorry did I put 12.5!) to power the two audio out channels.
As far as I can tell they are fed straight from a pcb mounted transformer....Leave a comment:
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LM317T Voltage Regulator Input Resistor Cremation.
Hi Folks!
I have a device with about 4 LM317T's which all seem to have tiny 10ohm SMD Resistors on their [B]voltage in[/B].
One particular one is doing about +33v down to 12.5v. However as soon as power is applied, the input resistor is toasted.
I tested across the resistor on the working ones, and it lowers the input voltage by only about .2 volts!
I've replaced this particular IC, but still no joy. I've not seen these devices used with such a resistor. Is it needed? And what could be causing their destruction?
Many Thanks... -
Re: Can you ID these?
Thank you stj,
I suspected they were good.
The audio ones are all the same, just 47uf 10v. There are no other caps other than 3 psu cans.
Nice one.
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Can you ID these?
Hi Folks!
Can anyone ID these surface mount caps. It's hard to tell if they are any good when they are only marked with the voltage and capacitance! Nothing on the underneath of the component either.
These are in a high quality separate audio DAC built in the 90's. So I'm looking to upgrade them for some nice new audio related ones
There are only two values.. 47uf 10v, and 6.8uf 35v.
The 47's have an ESR of around 0.20ohms, and the 6.8 between 0.80 and 1.20 which seems quite low. So perhaps there not bad, but they are obviously old.
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Re: PSU Woes - Need Help!
It's all over, it went up in smoke so a complete failure :/
However, seeing the machine is PowerPC based it only requires the usual 3.3, 5, 12v. So I plan to use a small ATX PSU instead.
So I didn't win this time, hey ho on with the next dead thing!
Thanks for your help, I did learn something from all this but I'm not quite sure what.
Cheers!
Leave a comment:
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Re: PSU Woes - Need Help!
It's the left circuit that freaks it out. Disconnect the left circuit and half the machine runs ok. With nothing connected it's exactly the same, as soon as the left circuit is connected you can hear the PSU restarting.
I replaced the left circuit IC and it half ran for the first time with the left circuit connected. However, I think I noticed a small puff of smoke and now it's back to square one. It lasted about 2 mins.
I may just junk this PSU and fit it with an old ATX one.
CheersLeave a comment:
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Re: PSU Woes - Need Help!
It does it with everything connected up and without anything connected. As long as the far left circuit is connected it freaks out.
Going to replace IC101 as I can't find anything else wrong.Leave a comment:
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Re: PSU Woes - Need Help!
Thank you for your reply.
No, when I replaced the fuses. Both on this board were blown and one on another. They never blew again once replaced, it just cycles every second or so making the chirping noise.Leave a comment:
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Re: PSU Woes - Need Help!
Once replaced, none of the fuses blew again.Leave a comment:
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