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General Category => Technical Support => Hardware related => Topic started by: blackdalek on 04:48, 25 February 21

Title: I think I killed my CTM644
Post by: blackdalek on 04:48, 25 February 21
I'm not sure how it happened, but my 5V socket in the front of the monitor is now outputting 0.26 V and the CPC6128 won't turn on.
All I did was put the probes of my multimeter onto the contacts to check the voltage and it read about 6.8 V. (not sure if that reading was too high for the 5V socket?)
Then I used the same multimeter to check a separate power supply which I am intending to use for the CPC (I'm planning on connecting an LCD monitor).I then went back to check the 5V socket on the CTM644 again, it was reading 0.26V.
What happened? Did my multimeter kill it somehow?
Title: Re: I think I killed my CTM644
Post by: pelrun on 07:11, 25 February 21
Any chance you accidentally shorted out the supply while probing it? I've done that before and it trips the protection circuit putting the regulator into shutdown. Power cycling the monitor usually restores it.
Title: Re: I think I killed my CTM644
Post by: blackdalek on 08:11, 25 February 21
That is possible. I haven't tried it again since I unplugged it.
I just tested it again and it is back to normal. I think I must have accidentally shorted it. I need new glasses ;)
Title: Re: I think I killed my CTM644
Post by: pelrun on 13:16, 25 February 21
That's good news.
Also, measuring open circuit voltage for a supply like this will give you an incorrect result, as it needs at least some current flowing to start regulating. That's most likely why you saw 6.8V on it - as soon as anything's actually connected it'll drop down to the real value.
Title: Re: I think I killed my CTM644
Post by: Bryce on 00:09, 26 February 21
That's good news.
Also, measuring open circuit voltage for a supply like this will give you an incorrect result, as it needs at least some current flowing to start regulating. That's most likely why you saw 6.8V on it - as soon as anything's actually connected it'll drop down to the real value.

It's not actually the regulation that's giving you a false reading, it's the fact that there is no load. It happens with batteries too that don't have regulators. A static (non-flowing) voltage will always be higher than the loaded voltage.

Bryce.
Title: Re: I think I killed my CTM644
Post by: pelrun on 07:46, 26 February 21
I'm pretty sure I said regulation wasn't occurring until there was a load, not that it was regulating to the wrong value.
Title: Re: I think I killed my CTM644
Post by: Bryce on 10:57, 26 February 21
I'm pretty sure I said regulation wasn't occurring until there was a load, not that it was regulating to the wrong value.

I didn't mean that it's regulating to the wrong value either. I was just saying that you will get higher values on ANY voltage source if it's not sufficiently loaded, even a battery. Linear regulators by the way usually need about 5mA before they are able to sense and stabilise the voltage correctly, however, they usually have a quiescent internal current of about 6mA so that they almost always are in a regulated state, even with very little load.

Bryce.