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Author Topic: ICOM AD-55 power supply output voltage adjustment  (Read 1309 times)

Offline alpard

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ICOM AD-55 power supply output voltage adjustment
« on: October 14, 2020, 1808 UTC »
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?

« Last Edit: October 15, 2020, 2236 UTC by alpard »

Offline ThaDood

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Re: ICOM AD-55 power supply output voltage adjustment
« Reply #1 on: October 14, 2020, 1851 UTC »
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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Offline alpard

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Re: ICOM AD-55 power supply output voltage adjustment
« Reply #2 on: October 14, 2020, 1937 UTC »
 I will open up the AD-55E, and see if I could see the voltage adjustment pot.
« Last Edit: October 15, 2020, 2237 UTC by alpard »

Offline alpard

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Re: ICOM AD-55 power supply output voltage adjustment
« Reply #3 on: October 14, 2020, 2051 UTC »
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. 

« Last Edit: October 15, 2020, 2232 UTC by alpard »

Offline ChrisSmolinski

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Re: ICOM AD-55 power supply output voltage adjustment
« Reply #4 on: October 14, 2020, 2141 UTC »
Did you measure the AD-55 voltage under a load?
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Offline alpard

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Re: ICOM AD-55 power supply output voltage adjustment
« Reply #5 on: October 14, 2020, 2309 UTC »
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?
« Last Edit: October 15, 2020, 2233 UTC by alpard »

Offline Stretchyman

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Re: ICOM AD-55 power supply output voltage adjustment
« Reply #6 on: October 15, 2020, 0853 UTC »
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.

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Offline alpard

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Re: ICOM AD-55 power supply output voltage adjustment
« Reply #7 on: October 15, 2020, 1511 UTC »
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.
« Last Edit: October 15, 2020, 2235 UTC by alpard »

Offline M0DOU

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Re: ICOM AD-55 power supply output voltage adjustment
« Reply #8 on: June 20, 2021, 2026 UTC »
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.


Offline redhat

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Re: ICOM AD-55 power supply output voltage adjustment
« Reply #9 on: July 08, 2021, 1716 UTC »
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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