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 Post subject: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: May Sat 20, 2017 6:53 am 
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Location: Florida
I have one of these 0-24 V, 1A supplies that I got from a junk shop 10 or more years ago. I don't have a schematic or PL and need to replace the voltage adjust pot (which seems to have been previously replaced with and audio taper one). I can wing it but it would be helpful to have the maker data.

Does anyone have a schematic and PL they would like to share?

Thanks,

RRM


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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: May Sat 20, 2017 1:26 pm 
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What is a PL ?


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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: May Sat 20, 2017 1:52 pm 
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Parts List I assume.

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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: May Sat 20, 2017 3:00 pm 
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Only a guess here, but if it's based around the LM317T adjustable voltage regulator, the adjust pot would be 5k ohms, linear taper rated at 1/2 watt.

http://www.st.com/content/ccc/resource/ ... 000455.pdf


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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: May Sat 20, 2017 9:16 pm 
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I found the manual for the "deluxe" model, 22-121
This model used the popular uA 723 / LM723 regulator.
https://elektrotanya.com/micronta_no.22 ... nload.html

Since Radio Shack often imported these from Taiwan you may find an op-amp" regulator circuit.
Later models incorporated the USA favorite, LM723 IC or as noted the LM317T series.
Micronta 22-123 Variable DC Supply.
Attachment:
File comment: Micronta 22-123
IMG_4104.JPG
IMG_4104.JPG [ 46.76 KiB | Viewed 3354 times ]

0 – 24 Volt, 2 Amp Bench Top Power Supply
DIY Project at Makezine.com : Uses the LM317T regulator.

Build a power supply from scratch.
by Michael Colombo
http://makezine.com/projects/0-24-volt- ... er-supply/


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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: May Sat 20, 2017 11:20 pm 
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Location: Latham NY 12110
I have one of these and I'm sure I have the schematic, I'll see if I can find it tomorrow.


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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: May Sun 21, 2017 1:18 am 
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Joined: Jun Sat 09, 2007 8:14 am
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Location: Florida
Thanks Lou, that would be great.

I looked inside and mine uses an LM723 and has a 5K linear pot for the voltage adjust. The reason I though the pot might not be stock is that the voltage adjust is non-linear. The output doesn't get to 5V until the pot is almost half way up and 10 V is about 2/3 of the way to max (24V). Other than that it seems to work fine overall and all the tweaks work.

The thing was so dirty and rusty I almost passed it up but it was cheap (maybe $5). I wound up throwing the cover away and making one from plywood. It's been handy.

RRM


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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: May Wed 24, 2017 1:39 am 
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Just a note. Even though everything seems ok now I'd still like to find a schematic and parts list if anyone has one.

Thanks,

RRM


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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: May Wed 24, 2017 1:08 pm 
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Sorry RRM, my unit is a 22-126 and uses discrete transistors and zeners instead of a chip.


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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: May Wed 24, 2017 10:55 pm 
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Thanks for looking, Lou. Looks like I need to get up the energy to trace the thing out and draw up a schematic.

RRM


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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: May Thu 25, 2017 4:31 am 
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Greetings to Lou and the Forum:

I used to have a 22-126; I just sold it at a garage sale.... too many low voltage supplies cluttering up the place. However, I did have to repair it when I got it and did reverse engineer it. If you would like the schematic, here it is:

Attachment:
Micronta Power Supply 22-126.pdf [52.01 KiB]
Downloaded 162 times


Regards,

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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: May Thu 25, 2017 11:33 pm 
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Thanks Jim, I do have the original manual for mine.


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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: May Fri 26, 2017 1:04 am 
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Is the negative terminal really connected to the chassis? That limits it's usefulness somewhat, especially for older PNP transistor radios.

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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: May Fri 26, 2017 1:49 am 
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Greetings to Marty and the Forum:

I believe the upside down non-filled arrowhead or triangle symbol that I used in the drawing refers to circuit ground, not chassis ground.

Regards,

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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: Mar Fri 09, 2018 10:10 pm 
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If you still need this info, the voltage pot has the following markings on it: 1377702 996-0057


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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: Apr Thu 23, 2020 1:04 am 
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I have a Radio Shack 22-123 variable power supply I just purchased and need some help.
Question:
How do I measure current ?

I checked the voltage over the range of 0-25 vdc and calibrated the gauge, but can not get the supply to measure current .
I have a copy of the owner's manual and the schematic. I also see that the PO has added an additional resistor, 0.56 ohm, in parallel to the 0.56 ohm per the schematic. I'm a little suspicious as this resister is in the current path.

Any help would be appreciated.
Ron


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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: Apr Thu 23, 2020 1:50 am 
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Joined: Mar Sat 03, 2007 12:53 am
Posts: 795
The meter on the power supply will not show any current unless a load is connected to the output of the power supply. You could connect a resistor or a small automobile instrument light (with the power supply set to 12 volts or the lamp may burn out), set the switch to the amps setting. The lamp should be lit and the meter should show the current drawn by the lamp. Auto head lights and tail lights would draw too much current from the supply.


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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: Apr Thu 23, 2020 3:14 am 
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Joined: Apr Thu 23, 2020 12:46 am
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Hi Alan,
Thanks for the quick reply. I tried the instrument lamp as you suggested and the amp function is working.
I was trying to use a car clock I had and it only draws about 13-14 mA. The gauge on this power supply starts at about 100 mA. Anything below 100 mA you can't read.

Thanks again,
Ron


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 Post subject: Re: Micronta 22-123 Variable DC Supply Schematic and PL
PostPosted: Apr Thu 23, 2020 9:52 am 
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Location: Sunbury, Ohio 43074
You could always get a $20 DMM. (25c at a garage sale) and use that for your current monitor. ;-)

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