troubleshooting case AC leakage

pukka

Member
2002-03-07 7:09 pm
Hi,

I post a message a while ago regarding my MD deck being unhookable to my waarde. I suspected about DC being on the outputs, but this is unlikely to be the problem (maybe is due to) as DC doesn't produce that kind of noise. And it won't reach the headphones however as the amp output is cap coupled...

I recently (painly!) discovered that the case underside has a tremendous AC leakage. Enough to cause considerable pain.

I already have the Service Manual (I'm going to replace the NJM2114D for AD826's plus other mods) and there's a mention of a very simple circuit to measure AC leakage (a 15k resistor bypassed by a 1.5uF, with one side to ground, and the other to the touching point, the DMM tips on each side) but they don't mention anything about places to check... only the mention of 500mA being the max admisible... uargh!

What things will you check first? Any hints will be helpful!

I could simply isolate the RCA terminals, but... why is it leakaging? BTW, the deck isn't earthed...
 

Alf

Member
2002-06-07 3:17 pm
Hiya, sounds like you have a real problem there. First, I would check your wall outlet and make sure it is grounded and polarized properly (watch this as some outlets are 'split'). Disconnect your eq from each other.Check each chassis for potential (AC) between the chassis and a good ground (like the ground on your wall outlet) with a multimeter. Try flipping the pwr plug over and test from chassis to ground again. You will find that there is more potential with the pwr plug in one direction than the other. Use the plug direction that presents the least potential. Do this with all your eq. With mine, I marked the wall outlet to indicate the 'hot' side, then marked each pwr plug with the right direction. I think you'll find that this will solve a lot of your problems. Good luck, Alf
 

Alf

Member
2002-06-07 3:17 pm
Yes, you are right! I must have missed that part as my other 1/2 was Mooin' at me all morning. Unplug the unit and check the pwr cord for damage and shorts to the chassis. To best do this, use a multimeter on the ohms scale with one lead on the pwr cord and the other to the chassis. If you see a dead short, start disconnecting the ac wireing one place at a time, working your way to the pwr transformer. You could have a primary winding shorted to ground in the transformer. Most units these days have transient suppersors and or disc caps that go from each side of the AC pwr, to chassis ground, one of these could be shorted or leaking. Let me know how you make out and what you find. DO NOT USE THE UNIT UNTILL YOU GET THIS FIXXED. IT POSES A FIRE HAZARD! OR, LIKE Tiroth says, COULD KILL YOU!