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Avondale m130 build

Johnathan
You really need to get yourself a higher wattage/Temp soldering Iron the soldering on the speaker terminals and RCA sockets is not good it looks cold to me
 
The one time that I have experienced smoke was from the 0R22 resistors
In my case the amplifier was oscillating due to a poor earth connection in the RCA lead that I was using for testing
 
Johnathan
You really need to get yourself a higher wattage/Temp soldering Iron the soldering on the speaker terminals and RCA sockets is not good it looks cold to me
thanks Alan, yes sometimes the heat is fine and flows well but on occasion it doesnt, not sure soldering them when mounted was the best option or not as the heat may of dissipated into the chassis.
 
on checking one of the amps mains disconnected, there is continuity if i place one probe on the 0v (toroid end) of the Cap6 board and parts of the ncc200 plus continuity between speaker posts
 
There should be no continuity between the speaker posts. You should be reading at least 0.5 Megaohms across output terminals.
The red and black plastic insulators should keep the posts insulated from the metal casework. One of the red insulators looks a bit distressed in one of your photos

Check that there is proper air space between all your spade connectors, the rear of the mains input socket and the audio input socket

Do you find the same readings on both amps?

With the Capo 6 boards disconnected from the NCC200 what voltages are you reading across + - 0v - minus

eddie
 
Jonathan

Do you mean +/- 53.5v relative to the 0volt rail That's a bit on the high side

I thought you said both boards were smoking Which NCC200 is giving strange results? Is it the repaired one with the burn marks or the one that did not suffer the blow out

eddie
 
Have you investigated fully the continuity between speaker output terminals Disconnect the speaker output lines spades from the NCC200 and the Cap6 and check the resistance between output terminals

Then measure the resistance between NCC speaker output terminal and the Cap6 0 volt terminal Compare readings between the two amps

eddie
 
Have you investigated fully the continuity between speaker output terminals Disconnect the speaker output lines spades from the NCC200 and the Cap6 and check the resistance between output terminals

Then measure the resistance between NCC speaker output terminal and the Cap6 0 volt terminal Compare readings between the two amps

eddie
There is no continuity between speakers posts when they are disconnected.
The resistance of the issue board is showing as 141k and the other slowly goes to about 12k, both tested without the speaker cables disconnected
 
Jonathan

Is the board without issues playing sweet music ? Remember to use some old (dare I say) expendable speakers for initial testing?
 
Jonathan

I would advise you read the following thread It seems poor connections at earth spades and signal earth are known reasons for the board going into oscillation and self destruction
Damaged NCC200-Left | pink fish media

If problem still persists then some investigation will be necessary

Google the "Dim Bulb Test"
Can you power the amp via an incandescent light bulb (60watts would be good) to effectively drop the applied mains voltage. Be careful with mains wiring Insulate everything properly etc
If this stops the smoke then it is likely that your bias current is too high.
This is most likely due to the applied relatively high DC rail voltages of 53.5 volts from your Cap6 boards

You may get away with reducing the bias current by rotating the bias current setting variable resistor on the board
It is a small blue component in the middle of the board labelled Set Bias
You could try turning the little screw anticlockwise to reduce the bias current. If I remember correctly the NCC 200 should run at approx 100mA which gives a voltage of 22mV across the 0R22 resistor
You will not be able to reach this value with the bulb in series but at least it will give us some idea of what is going on

The other possibility is that your wiring configuration ( it does look a bit messy) is causing some coupling between input and output which is causing the board to go into oscillation

I would add that I sold you the boards in good faith believing them both to be in proper order (although I never tested the repaired board) as I had already fitted my NCC220 replacement boards
I'm happy to refund you if that's your preference as long as you don't totally destroy them. I think though that it would be unwise for you to plug in some new boards into your existing setup as there is a real risk you would damage them. Best persevere and find what is going on with your current setup

eddie
 
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dont worry Eddie, im not in the game of blaming others for a process im carrying out.
i will persevere, it seems odd that when powered there is no problem. so maybe as suggested above it may be to do with the RCA being used.
 
If I remember correctly the NCC 200 should run at approx 100mA which gives a voltage of 22mV across the 0R22 resistor

The NCC200 has a Bias current of 34-38mA

Alan
 


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