I power up the NAD 3130 with my newly built 100W Dim Bulb Tester Today, the bulb flashed and went out and the green LED on the front was illuminated much to my delight. I then attached my MM to the left speaker output but no voltage, then noticed the speaker switch was off, selected speakers A & B then the bulb slowly got brighter and I saw the magic smoke from around Q411, it appear I have a short again. I removed the MJ2955 & 2N3055 to see if I had damaged them but both appeared to test fine on my parts tester (photos below) got them off Ebay could I have fake power transistors?
I also noticed that Q421 1000uf 6.3v was bubbling from the top vent, could this be over voltage, however, I don't see any voltages on the service manual schematic? I will test Q411 and surrounding parts tomorrow, could the speaker switch be faulty or can you suggest what I need to check next?
David..
I also noticed that Q421 1000uf 6.3v was bubbling from the top vent, could this be over voltage, however, I don't see any voltages on the service manual schematic? I will test Q411 and surrounding parts tomorrow, could the speaker switch be faulty or can you suggest what I need to check next?
David..
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You need to find out what smoked. Could it be that bubbling cap?
Unlikely the speaker switch is faulty. It would have to be directly shorting the amplifier output to ground to cause a problem. Worth checking there is no wiring issue causing that.
The cap bubbling is caused by either a high DC offset or an offset of incorrect polarity. I would suggest you link the vbe multiplier out to force zero bias. The bulb increasing in brightness points to the bias current increasing (thermal runaway) although having a speaker connected with an offset would also draw current.
Ultimately 99% of NAD faults are failed output and driver transistors and also the Q405/407 pair.
The outputs should be OK as the bulb will have saved them. If you bought them from an authorised supplier they will be to spec and genuine, if bought off eBay then they could be anything.
Unlikely the speaker switch is faulty. It would have to be directly shorting the amplifier output to ground to cause a problem. Worth checking there is no wiring issue causing that.
The cap bubbling is caused by either a high DC offset or an offset of incorrect polarity. I would suggest you link the vbe multiplier out to force zero bias. The bulb increasing in brightness points to the bias current increasing (thermal runaway) although having a speaker connected with an offset would also draw current.
Ultimately 99% of NAD faults are failed output and driver transistors and also the Q405/407 pair.
The outputs should be OK as the bulb will have saved them. If you bought them from an authorised supplier they will be to spec and genuine, if bought off eBay then they could be anything.
I found what smoked on the dead side, it was the B649a I also replaced Caps C428,C427, C426 and C425 all reading low with a high ESR. I still had the MJ2955 & 2N3055 removed (Looks Like I fitted fakes) and the newly fitted dead B649a, I'm now suspicious of the new replacement B649a and D669a (Ebay) Photo's below?
When testing yesterday the good side stoped working and had a very loud buzzing, I decided to remove the new replacements B649a and D669a (Ebay) from the working side and refitted the BD140 & BD139. I found that after removing the dead B649a and replacing the Caps above the unit power on the DBT with one quick flash and I had sound on all inputs and no short when I selected Speakers A, B or A+B.
I'm now thinking I could remove the working MJ2955 & 2N3055 and fit them to the dead side to see if I have Fakes or not? Is there a way I can test any of the the Transistor I have purchased from Ebay, obviously my components test only confirms what it is NPN/PNP and basic stats?
I have looked for genuine MJ2955 and 2N3055 online at RS, CPC, Farnell etc it looks like the Mj2955 is difficult to obtain, Some require a minimum purchase of 10 that's £30 + ! Does anyone have any for sale or can recommend a cost effective supplier?
The new B649a has no metal back I noticed when removing it, but the D669a has. Please have a look at the photo's below and give me you option if you think I have fakes or not??
Regards
David
When testing yesterday the good side stoped working and had a very loud buzzing, I decided to remove the new replacements B649a and D669a (Ebay) from the working side and refitted the BD140 & BD139. I found that after removing the dead B649a and replacing the Caps above the unit power on the DBT with one quick flash and I had sound on all inputs and no short when I selected Speakers A, B or A+B.
I'm now thinking I could remove the working MJ2955 & 2N3055 and fit them to the dead side to see if I have Fakes or not? Is there a way I can test any of the the Transistor I have purchased from Ebay, obviously my components test only confirms what it is NPN/PNP and basic stats?
I have looked for genuine MJ2955 and 2N3055 online at RS, CPC, Farnell etc it looks like the Mj2955 is difficult to obtain, Some require a minimum purchase of 10 that's £30 + ! Does anyone have any for sale or can recommend a cost effective supplier?
The new B649a has no metal back I noticed when removing it, but the D669a has. Please have a look at the photo's below and give me you option if you think I have fakes or not??
Regards
David
The old 2SB's and 2SD's went out of production decades ago as far as I remember. I would lay odds on the eBay ones being fake, they certainly look highly suspect.
I think I would consider fitting more modern generic replacements all round tbh.
I think I would consider fitting more modern generic replacements all round tbh.
You could try Profusion for 2SB/SD equivalents; https://www.diyaudio.com/community/...for-2sb649ac-and-2sd669a.380762/#post-6884090
Well I wouldn't overthink it 🙂
BD139/BD140 to replace the 2SD/2SB's. The T03 outputs are more problematic in one off's and I can't just spot any possibles from the usual UK suppliers.
You could maybe try MJ15015/16 (or the G versions) for the TO-3's ? CPC & Cricklewood Electronics are both still listing them.
Just placing an order with CPC andI see two listings for the 2N3055 and 2N3055G which should I order?
you can normaly tell if they have the hometaxials, the RCA ones generaly are.If they have the older motorola ones fitted then they wont be
And i would suggest you do what @Mooly suggests and fit the emmiter resitors if they are RCA ones(they will have an 'H' on them)
the 669A and 649A are readily available, i get mine from cricklwood electronics, never had an issue
one thing to always check with the 3130 is the regulated supply, the transistors,especialy the PNP will be loose and need re soldering, this is one of the main causes of failure in these amps
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I have order the genuine parts needed from both CPC and Cricklewood. What’s the opinion on fitting ceramic variable resistors to adjust the idling current instead of adding and removing resistors?
Not tried them, should be OK. Better off getting them from Cricklewood, and you will need to fit emmiter resistors with them
