noisy DID's

[Fixin]

Does anyone know of a good isolation transformer to block noise comming in on the AC? My DID's are so noisy you can't use them. When I run the IPK off of batterys it clears up nice. I even tried floating the ground with no luck. I tried UPS as well.

 

[OzzieGeorge]

Sounds like you need line isolation transformers. Normally the line is balanced but a common problem with such things as lightning damage or other overvoltage damage is that the balancing circuit gets damaged. this results in the type of noise you are experiencing but the solution is expensive and often it is cheaper to replace the card with the problem. Try swapping cards to see if the problem moves. If it does then make the decision.

Commonly the cost of one transformer down here is $300-400 so if multiple ccts are damaged it can be cheaper to change the card.

 

[Fixin]

Cutting a strap on the card solved 75% of the problem.

 

[OzzieGeorge]

Don't you hate it when you type a post and it disappears.

Which strap did you cut, and was it associated with the line balancing circuit.

I must have been a little inebriated when I first posted on this as they are not called line isolation transformers, they are called line balancing coils.

Analogue indial is still quite common down here, although currently being phased out, and this fault is quite common with this type of circuit. Changing the card or fitting the coils both of which is expensive are the only options I know of.

I was once told that if you return a card with this fault to NEC it would come back unrepaired as it wasn't a requirement for this type of circuit under our regs. I don't know how true that is though.

 

[Fixin]

This is an undocumented cure for AC leaks on DID card. The strap is S1 and located on the bottom edge of the face of the card. Some cards I have found do not have this strap. We cut the strap as well as put SNC chokes on the DID's and noise is considerably less, but still there. We are looking at conditioning the AC power as well.

 

[dontworx]

When you said you floated the ground, did you actually unscrew the AC ground strap on the front of the elite?

 

[Fixin]

Yes. It didn't help. They work great running off the batteries. I have some SNC chokes on the lines too. They quieted them down even more. Still has some noise though. We are going to try to condition the AC with an isolation transformer.