So I need to replace the following voltage regulator in an old Atari as it's registering 0.5V between output and ground and 24V on the input, but it's supposed to be providing 12V on the output side of things.

Voltage Regulator UA78M12UC

I'm trying to establish whether either of the following (locally available) parts are suitable replacements:



I'm a complete newbie to electronics (I'm a software guy) but I've read on here that the M is for Medium current, so I'm guessing that the 3A regulator I linked to would be capable of the job, but figured it'd be better to ask than to burn out some other component.


What do the parts of the component code mean? I guess the 12 in UA85M12UC means 12V, but I have no idea about the UA78 and UC!


3 Answers 3


Your first item (the MC78T12) would be a suitable replacement for the 78M12.

UA indicates the manufacturer (Fairchild, I think). Many manufactures make this series of regulator, and all makes should be interchangeable.

78 indicates a series of linear voltage regulators

M is low current (500 mA), so the 78T12 is a bit of overkill...

12 is the output voltage

UC is the package type (TO-220) (different makers use different package codes, just to confuse the user :-) )

Your second link is to a switching regulator - a quite different type of beast.

  • \$\begingroup\$ Soldered one of these in place tonight and it's working a treat. Thanks for the details on the codes! \$\endgroup\$
    – Matt Lacey
    Aug 19, 2014 at 10:52
  • \$\begingroup\$ I would have used a run of the mill 7812 with 1A rating. \$\endgroup\$
    – starblue
    Aug 19, 2014 at 20:48

The MC78T12 should work fine, if it's the regulator. There's no guarantee there isn't something else dead that's causing the output to go to 0.5V though.


The UA is actually stands for microAmp uA. In 7812 The 78 is Positive Voltage Regulator of 12 volts. So a 7805 is a 5v Positive Voltage Regulator. If you were interested in using something like an opamp that uses a split supply (needs a positive and a negative supply) you could use a 7812 and a 7912. Where the 79 is Negative Voltage Regulator and 12 is -12v. you would need one of each. The m is for milliamp. This is a 12 volt regulator that can supply 500mA of current. In the future, a quick google search will tell you what you need to know, or at least where to get the data sheet. Datasheet for UA75M12

  • 2
    \$\begingroup\$ "UA is actually stands for microAmp uA" no it does not, not in a part number. "The m is for milliamp" no it does not, not in a part number. This is a deeply confusing answer. A negative voltage regulator is not needed. \$\endgroup\$
    – gbulmer
    Aug 19, 2014 at 2:26

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