Analog/Digital Trainer PAD-234A Voltage Regulator Maintenance

Thread Starter

BMB280

Joined Mar 2, 2021
4
Hello. I'm having trouble with my Analog/Digital Trainer Pad-234A. The 5V output is not working right. When I power on the trainer, the +12V and -12V outputs work but the 5V output does not, the indicator light is not on and it's only outputting about 1.4V. I've tried changing the fuse and that didn't work. I think the voltage regulator needs to be fixed or replaced. How would I go about doing that? Thanks.
 

dl324

Joined Mar 30, 2015
13,282
I've tried changing the fuse and that didn't work.
The fuse interrupts line voltage. If it was bad, nothing except the power on indicator would have been working.
I think the voltage regulator needs to be fixed or replaced. How would I go about doing that? Thanks.
The power supply section is simple. Checking the voltages on all three terminals of the 5V regulator will tell you which components might be bad.
PAD234PowerSupply.jpg
It appears that the voltage regulators are mounted on the chassis. If that's the case, the case of the 5V regulator will be the output.

If you need to open the case, take care not to touch anything on the primary side of the transformer. Lethal voltage will be present.
 

twohats

Joined Oct 28, 2015
249
You need to check REG 3, are there volts going to it? (Should be more than 5v probably 10v).
If not, BR 2 & C9. If yes, Reg 3 LM7085
As mentioned above, take care.
Good luck..
 

Irving

Joined Jan 30, 2016
2,173
If this is truely c1994 its more than likely there are issues with C9 and/or C10 going off... The 7805 is unlikely to be at fault, they are pretty hard to kill.
 
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