Grounding Problem
Normal troubleshooting you will place your black probe to the equipment chassis or cold ground to take voltage measurement. When you do troubleshooting especially on the board where you have removed it from the equipment, make sure you are certain where to place the black probe. The reason i mention this is because sometime a repair tech can get confuse of the grounding. If you place your probe on point A (see the photo above) and measure the output voltage then you will not get any result. You should place your probe on point B which is the cold ground. From the photo, there is a slight confusion between point A and B. So before you start to make any voltage test make sure that you place your black probe on the right point. If you still uncertain which one is the ground, just refer the filter capacitor negative pin and you won’t get wrong.
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Vic
February 19, 2012 at 12:31 pm
I seem to be a little confused about the last sentence. It states "If you still uncertain which one is the ground, just refer the filter capacitor negative pin and you won’t get wrong." The problem is my understanding is that the capacitor negative pin is a hot ground and not a cold ground. The hot ground should only be used to measure primary side voltages. All secondary voltages should use chasis (cold)ground. Reversing the grounds will give you incorrect reading and can even damage your meter. Please tell me your thoughts.
Thanks
Vic
admin
February 20, 2012 at 9:36 am
Hi Vic,
Capacitor negative can be hot or cold ground. Since the above article is referring to check the output voltage this mean it is referring to cold ground which is in secondary side. You are right, if one wants to check on the primary side then the black probe should be placed at the negative pin of the primary side big filter capacitor.
Jestine
Vic
February 26, 2012 at 3:05 pm
Hello Jestine,
Thats for clearing that up. That makes sense now. The only thing is most capacitors on the secondary side are solder so close to the board that its impossible to get to the negative leg. The solution would be to turn the board over and either solder a test wire to the negative solder pad or connect your test directly to that pad.
Thanks again
Vic