I have replaced some more caps this afternoon and R456/R458 junction is now reading -31v and -26v on other side of R456. How would attempting to set the idling current have caused this issue and C432 reads 47uf 35v on the schematic and listed 47uf 63v in the listed components?
I would suggest mooly is correct, that junction I said to check should be about -22v
Ok, but is the -30v correct on the other side and if I have fitted the incorrect value resistor at RX2 could this be the cause of the high voltage at R458?
RX2 and the bias current should have no effect on the voltages provided it is not massively excessive and killing something.
R456 and R458 so see equal voltage across each.
The circuit diagram gives no marked voltages but working backwards to the power supply it seems you should have around -25v or so based on the fact there is a 22 volt Zener and series LED. Those two components would generate around -25 volts as a reference for that rail. Worth checking and if that is not the rail value then can you measure what is across that Zener.
R456 and R458 so see equal voltage across each.
check this cap as ive had them go before
you will know if you have lost the rail, you will have a neg voltage the + side of R460
just use the higher voltage cap, it wont make any difference but 35v is sufficient
Thank you again for your reply, I looked at the schematic this morning and removed D501 and tested it prior to your reply and it tested ok. I then followed the circuit and you had marked and compare and retested around R456/458 to the working side and found two cracks in the connection to Q414, this area had been worked on before me. The solder joint looked ok but was not making a connection with the Base or Emitter, removing the solder exposing the trace and resoldering appears to have restored things..
I tested for the mV on RX2 and had around 12mV on a brief test, I need to again attempt to set the correct level, previously I used 500 ohm variable resistor, how would you recommend I set the voltage on RX2?
I tested for the mV on RX2 and had around 12mV on a brief test, I need to again attempt to set the correct level, previously I used 500 ohm variable resistor, how would you recommend I set the voltage on RX2?
I would recommend doing what you are doing now and using a preset. Err on the low side as a final result in the interests of reliability. You won't hear any difference if you set it at 10mv or 30 mv so aim on the low side. Recheck the value when the amp is hot after playing loudly for a few minutes. If it has crept up then bring it back down even if that means its a little low when cold.
Yes, the higher RX1 and RX2 and the more the bias generator transistor turns on which in turn lowers the voltage across the transistor which in turn lowers the bias current.
I think I have finally fixed this amplifier, refitted the pre set resistors on both sides and RX1 was reading 27mV so I match the fail side RX2 to 27mV, I decided to leave the preset resistor in place? I let the amplifier run for around 20 mins, the levels and both sides remained at 27mV as you can see from the attached photo.
I was only running a pair of small book shelf speaker and playing music off my iMac and not my Thorens TD150 and was pleasantly surprised by how punchy & crisp this amp sounds considering its age and only 30W per channel, I'm looking forward to attaching this to my Linn speaker and testing out the MC Phono stage.
Thanks again for all you help in resurrecting this old NAD 3130.
Regards
David.
I was only running a pair of small book shelf speaker and playing music off my iMac and not my Thorens TD150 and was pleasantly surprised by how punchy & crisp this amp sounds considering its age and only 30W per channel, I'm looking forward to attaching this to my Linn speaker and testing out the MC Phono stage.
Thanks again for all you help in resurrecting this old NAD 3130.
Regards
David.
I would replace those 2 no 330uf cap on the regulated supply and the 2no .68uf caps by the bass control (the orange ones) normally well out of range. You will find them hard to get hold of
I put back foil caps, they are fine to use👍
I put back foil caps, they are fine to use👍
The 330uf are fine but as you said the 0.68uf will need replacing. I don’t have replacements yet, but you said you fit foil replacements, I’m a little confused as I have electrolytic cap fitted and I believe foil are not electrolytic.