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Technical Topics => The RF Workbench => Topic started by: alpard on October 14, 2020, 1808 UTC
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Hi All
I checked my ICOM AD-55 output voltage, and it is 20V.
This is too abnormally high voltage I thought.
Is there ways to lower the voltage on the AD-55?
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Wow... Somethin' ain't right there. Well, open that up and look for, either an adjustment POT, or for cold solder joints by a Zener Diode, or an LM78##-like Voltage Regulator. Just for the heck of it, have you put it to a load, like a 12VDC light bulb, and measured the voltage under load? Not having that power supply myself, I'm just speculating, but hopefully enough to help.
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I will open up the AD-55E, and see if I could see the voltage adjustment pot.
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Wow... Somethin' ain't right there. Well, open that up and look for, either an adjustment POT, or for cold solder joints by a Zener Diode, or an LM78##-like Voltage Regulator. Just for the heck of it, have you put it to a load, like a 12VDC light bulb, and measured the voltage under load? Not having that power supply myself, I'm just speculating, but hopefully enough to help.
Thank you for your advice. I have opened up the AD-55E, and there was no pot to adjust the voltage.
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Did you measure the AD-55 voltage under a load?
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No, haven't done it yet. I wouldn't imagine the output voltage from the AD-55 would drop a lot under the load. Would you?
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A schematic would be useful!
However if it's a simple pass transistor linear jobbie then the smoothing cap may be shot and passing A.C. ripple, just a guess.
Put your meter on A.C. see anything? If you do it's the cap.
Str.
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Great idea on reading AC from the output DC. If the smoothing cap is bad or diodes are bad, then it will show
solid AC voltage readings. Will try that.
I don't have the schematic, and couldn't find it anywhere.
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Just found this post after measuring two acquired Icom AD-55 power supplies to check voltage and polarity was correct before using it on my Icom R75 receiver.
Both measure around 20V output. This does seem a bit high but might be by design, if you look at the circuit diagram for the R75, the input voltage goes straight into a couple of voltage regulators (14V and 5V).
Checking the datasheets for these shows they can handle up to 30V input which is well above the 20V input.
Still, I'm a little surprised and disappointed, I'd have expected the NS-55 to be properly regulated at 13.8V given it is manufactured by Icom and is labelled as such on casing.
I probably won't use them as it's only going to generate excess heat from the R75's regulators and reduce their lifetime.
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Doesn't surprise me. I've seen more than a few questionable designs come out of icom over the last few decades. From filter boards that zorch and smoke, to things like this...no thanks.
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