ICOM AD-55 power supply output voltage adjustment

[alpard]

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?

[ThaDood]

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.

[alpard]

 I will open up the AD-55E, and see if I could see the voltage adjustment pot.

[alpard]

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. 

[ChrisSmolinski]

Did you measure the AD-55 voltage under a load?

[alpard]

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?

[Stretchyman]

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.

[alpard]

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.

[M0DOU]

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.

[redhat]

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.

+-RH

[Quin]

I discovered similar readings. My AD55A has 19.57V. Seems weird that ICOM would have that set since it is outside the +/-15% range they spec on most receivers and transceivers. I have moved to a SMPS I have built myself. Also working on two dual SMPS boxes for my other radios.

[~SIGINT~]

The instruction sheet can be found on the ICOM site: https://www.icomjapan.com/support/manual/1794/
and state an output of 15 VDC +/- 5% at 2 Amps.

I doubt that you will find any adjustments in this power supply. Photos at the link bellow.
https://www.dxengineering.com/parts/ico-ad-55ns

[RobRich]

I have seen unregulated 12vDC wall warts at 17-18 volts unloaded, and some models can reportedly hit 20+ volts. o.0

Anyway, about the original AD-55(A), at least for the version shipped with earlier R75 models....

Alas, the linear "transformer" version of the AD-55A floor brick power supply (USA versions) is unregulated and provides way too much voltage even fully loaded (which we measured at 17.65 volts which is way over specs.). So the set runs very warm to near HOT after awhile as the internal voltage regulator has to burn this excessive voltage off.

Source: https://www.qsl.net/n9ewo/icr75.html

Later production R75 models shipped with the AD-55S-12 switching power supply.