HFU HF Underground

Technical Topics => The RF Workbench => Topic started by: alpard on October 14, 2020, 1808 UTC

Title: ICOM AD-55 power supply output voltage adjustment
Post by: alpard 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?

Title: Re: ICOM AD-55 power supply output voltage adjustment
Post by: ThaDood 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.
Title: Re: ICOM AD-55 power supply output voltage adjustment
Post by: alpard on October 14, 2020, 1937 UTC
 I will open up the AD-55E, and see if I could see the voltage adjustment pot.
Title: Re: ICOM AD-55 power supply output voltage adjustment
Post by: alpard 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. 

Title: Re: ICOM AD-55 power supply output voltage adjustment
Post by: ChrisSmolinski on October 14, 2020, 2141 UTC
Did you measure the AD-55 voltage under a load?
Title: Re: ICOM AD-55 power supply output voltage adjustment
Post by: alpard 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?
Title: Re: ICOM AD-55 power supply output voltage adjustment
Post by: Stretchyman 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.

Str.
Title: Re: ICOM AD-55 power supply output voltage adjustment
Post by: alpard 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.
Title: Re: ICOM AD-55 power supply output voltage adjustment
Post by: M0DOU 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.

Title: Re: ICOM AD-55 power supply output voltage adjustment
Post by: redhat 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.

+-RH