LC II TDK PSU 18v?

[mst3k]

Greetings,
I have three TDK PSU’s from various LC’s.
I’ve recapped all three. All had low voltage and wouldn’t power on my LC II.
After recapping, two of them work perfectly with the correct voltages and power my LC II without issue.
The third shows correct voltages on the 5 volt side but the 12 volt rail has jumped to 18 volts.
I replaced ALL of the caps and have double checked polarity but everything looks right.

Why would the 12v voltage jump so high?

Thanks in advance for you help!

 

[mst3k]

Ok. I've double checked everything on the recap and cleaned the board, again, with q-tips and alcohol.
Now, weirdly, the 12v rail is down to 15v. The 5v's are steady at +5.02v and -4.99v.
Maybe I'll just keep cleaning the board until the voltage genie gives up three more volts.

 

[Phipli]

Ok. I've double checked everything on the recap and cleaned the board, again, with q-tips and alcohol.
Now, weirdly, the 12v rail is down to 15v. The 5v's are steady at +5.02v and -4.99v.
Maybe I'll just keep cleaning the board until the voltage genie gives up three more volts.

Have you got a load on the PSU? Some don't give proper voltages unless they're loaded.

 

[mst3k]

Have you got a load on the PSU? Some don't give proper voltages unless they're loaded.

Yes. I have it connected to the LC2 when I measure. I've tried it with a drive attached too.
It's the same setup as the other two TDK PSU's that spec out perfectly.
It makes me a little nervous because I don't know what 15v-18v will do to the machine, so I run it just long enough to get my readings and power off.

 

[Phipli]

Yes. I have it connected to the LC2 when I measure. I've tried it with a drive attached too.
It's the same setup as the other two TDK PSU's that spec out perfectly.
It makes me a little nervous because I don't know what 15v-18v will do to the machine, so I run it just long enough to get my readings and power off.

If you have a load of testing to do you could get some 10W resistors and use them to load the voltages appropriately based on the PSU ratings. You don't need to fully load them, but if you work out resistor values that will say, perhaps, put 1/4 of the rated power for each voltage?