Q1.R.C.D. tripped by disco decks.

I can't understand how a fault on the 15 Volt side of the power supply circuit board can cause an R.C.D. trip.

Maybe a short between the primary and secondary of the transformer? - the circuit the completing via the ELV side's PE link.

   - Andy.

Although thinking about it, that should have shown up on the insulation test, presuming the ELV's "Earth" is the LV's side's c.p.c.

   - Andy.

Although thinking about it, that should have shown up on the insulation test, presuming the ELV's "Earth" is the LV's side's c.p.c.

   - Andy.

The transformer seems to be o.k. No connection by wire insulation breakdown from primary to secondary at 500Volts. The primary windings are 0-120V 0-120V. 103 and 97 Ohms respectively.

The two secondary windings are reading 13V and 13V off load.

The two 1000 micro Farad power supply smoothing capacitors test at about 950 micro Farads each by an Atlas tester.

I am still puzzled.

Perhaps this unit operated o.k. on a non R.C.D. protected supply and it is just now that I have found a fault. I did change the R.C.D. and the same fault occurs.

Z.

Eurica! I believe the problem is due to the disco desks being supplied from one R.C.D. protected circuit, but the amplifier is supplied by a different R.C.D. protected circuit.  When the screened audio cable is installed between the decks and the amplifier one R.C.D. does not like that and trips. The screen is earthed.

An inline digital multimeter set to A.C. milli-Amps shows zero current when installed in the decks' earth wire (C.P.C.).

Z.

Why can't we quote any more? 

In line multimeter (rather than clamp meter) is a bit brave! I have to admit, however, to doing the same on a 2-way (flickering) lighting circuit. Current was 1 mA when the switches were off.

Brave, Oh yes. That's me all over. Inline is more accurate to  my mind Chris. I started off on a 20 Amp range, then switched down to 200mA in stages.

Z.

Use the cursor to highlight text you are interested in and a new "quote" option appears.

Although when I try it I keep getting an error message, and have to delete the quote before my reply will work. 

Chris Pearson said:

Why can't we quote any more?

You can - either as 2400 says you can highlight and use the Quote pop-up button, or just copy & paste into your reply the bit you want to refer to, select that and use the Formats->Format->Blocks->Blockquote to make it a quote.

   - Andy.

Eurica! I believe the problem is due to the disco desks being supplied from one R.C.D. protected circuit, but the amplifier is supplied by a different R.C.D. protected circuit. 

Humm. Any ELV current between the two boxes still shouldn't be finding its way through either RCDs coils ... unless there's another fault somewhere.

   - Andy.

Having plugged the unit into just one supply via just one R.C.D., albeit a 100mA type, there is no tripping at all and the unit is working well. I am still puzzled as to why the tripping happened in the first place. The unit showed no earth leakage at all with my in line multi-meter.

Z.

I presume you do not really mean 'unpowered'  do you ?

So which RCD trips - the one for the deck motors or the one for the audio ? The audio cable braid/screens being at mains earth potential is perfectly normal & reasonable - and I;d expect it to be more or less the same if the amp and the deck are connected to each other or not. So with that audio lead unplugged at each end in turn as a means to get onto the audio cable screen, how many volts between amp input earthy side, and deck output, earthy side of connector. (turn the amp volume down so that you do not blow anything with a large 50Hz pick-up during this test.)

And then if not the same, which is furthest volts wise from supply CPC ?

The electrolytic caps do not worry me, and unless bulging, leaking or measuring voltages above their label rating, will be fine as they are  -  a center grounded DC supply is a normal thing to find on an audio system - it allows the speakers to both blow and suck equally when the drums go bang, but no text book will describe it thus. 'DC coupled symmetrical push-pull'' is more likely...

You can have a single sided DC supply but then you need to AC couple the outputs, limiting the LF response and offending the purists.

Caps in the mains side of things from L-E or N-E should be treated as far more suspicious,  (or surge arrestors in the same positions )especially if more than a few tens of nF

I do not think you have found it yet, in effect you have a symptom, not an explanation.

Mike.

Thanks Mike. The "unpowered" refers to the decks not having an audio amplifier. An external one is needed. "Powered" decks have a built in audio power amplifier.

The amplifier runs through a 100mA R.C.D. and the record playing double decks run through a 30mA R.C.D.

I will examine things more thoroughly.

Z.