Hey folks,
I have a NAD 3130 that I just cannot get working properly. It smoked randomly one day, I opened it up and found that the output devices on the left channel had shorted out, so I ordered a new MJ2955 and 2N3055 on eBay. I replaced Q413 and Q 411 which were both shorted, and replaced R459 which was burnt.
I then turned it on with a dim bulb tester - and got a very bright light!
Turned it off and found that Q407 was leaky/partially shorted - so i decided to replace that and also Q409 for good measure. I also had spares for Q405, Q401 and Q403 so opted to replace those too even though they measured fine. Additionally i replaced C 421 which looked ever so slightly bulged.
Turned it on again with dim bulb tester, this time It switched on with a nice green light on the front, but that light quickly faded out and the dim bulb began to light up - no where near as bright as before but still definitely too bright. If i leave it in this state, Q417 and Q415 heat up to around 50c in 5 minutes and seem to stabilise there. As this happens, the voltage on them goes from about 20v to 30v, and the bulb tester goes dimmer and dimmer. Eventually the green light on the front switches back on. The center voltage adj pots seem to be dead as turning them does nothing, however both channels are reading around 35mv on outputs - not ideal but definitely not the cause of my problem. The idling current is 0.2mv (!!!) on the left (bad) channel, and about 5mv on the right channel.
I have tested EVERY resistor on the left channel against the right - they all read the same values. I have performed diode meter checks across all capacitors - no shorts. I've checked the two zener diodes - all fine. Can anyone help me figure out what I've missed? I feel like I'm so close but there's just one thing left I can't find.
I have a NAD 3130 that I just cannot get working properly. It smoked randomly one day, I opened it up and found that the output devices on the left channel had shorted out, so I ordered a new MJ2955 and 2N3055 on eBay. I replaced Q413 and Q 411 which were both shorted, and replaced R459 which was burnt.
I then turned it on with a dim bulb tester - and got a very bright light!
Turned it off and found that Q407 was leaky/partially shorted - so i decided to replace that and also Q409 for good measure. I also had spares for Q405, Q401 and Q403 so opted to replace those too even though they measured fine. Additionally i replaced C 421 which looked ever so slightly bulged.
Turned it on again with dim bulb tester, this time It switched on with a nice green light on the front, but that light quickly faded out and the dim bulb began to light up - no where near as bright as before but still definitely too bright. If i leave it in this state, Q417 and Q415 heat up to around 50c in 5 minutes and seem to stabilise there. As this happens, the voltage on them goes from about 20v to 30v, and the bulb tester goes dimmer and dimmer. Eventually the green light on the front switches back on. The center voltage adj pots seem to be dead as turning them does nothing, however both channels are reading around 35mv on outputs - not ideal but definitely not the cause of my problem. The idling current is 0.2mv (!!!) on the left (bad) channel, and about 5mv on the right channel.
I have tested EVERY resistor on the left channel against the right - they all read the same values. I have performed diode meter checks across all capacitors - no shorts. I've checked the two zener diodes - all fine. Can anyone help me figure out what I've missed? I feel like I'm so close but there's just one thing left I can't find.
Could be oscillating. Do you have a scope?
Make sure the new outputs are genuine. When you got them through ebay chances are high they are fakes.
Make sure the new outputs are genuine. When you got them through ebay chances are high they are fakes.
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No scope unfortunately.
Oh really? The new outputs measure similarly to the ones on the right channel in terms of diode mode... does that mean anything?
Oh really? The new outputs measure similarly to the ones on the right channel in terms of diode mode... does that mean anything?
Maybe your bulb is the wrong size.
Try a bulb rated at least twice the maximum AC line wattage draw of the amplifier.
Try a bulb rated at least twice the maximum AC line wattage draw of the amplifier.
The bulb tester limits the AC line current to (bulb wattage)/(AC line voltage).
Test all of the parts before replacing any of them. Most amplifiers will have cascading failures.
Check junctions of semis both forward and reverse. On transistors also check CE with the diode function..
Sometimes the CE can be shorted, but the BE and BC junctions will still be ok.
You can disconnect one amplifier channel from the power supply, and test the other channel independently.
You can also compare readings on the the good channel with the bad channel.
Test all of the parts before replacing any of them. Most amplifiers will have cascading failures.
Check junctions of semis both forward and reverse. On transistors also check CE with the diode function..
Sometimes the CE can be shorted, but the BE and BC junctions will still be ok.
You can disconnect one amplifier channel from the power supply, and test the other channel independently.
You can also compare readings on the the good channel with the bad channel.
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Thanks for the response.
I'm aware of how a bulb tester works. Your first message seemed to be suggesting that perhaps it was just getting bright because I had used a bulb with too low of a wattage - I pointed out that this couldn't be the cause, as the problematic channel was heating up significantly.
I'm aware of how a bulb tester works. Your first message seemed to be suggesting that perhaps it was just getting bright because I had used a bulb with too low of a wattage - I pointed out that this couldn't be the cause, as the problematic channel was heating up significantly.
As stated in the post - I have replaced all transistors in the channel, the majority of which were shorted, and the last three because it was easily done.
Also stated - I have compared readings between every component i can think of on both channels.
Then list here all the DC voltages on all of the amplifier semis for both channels.
Maybe the output stage bias transistor Q410 is not working right.
That bias circuit is kind of wonky anyway.
Maybe the output stage bias transistor Q410 is not working right.
That bias circuit is kind of wonky anyway.
ok, will do. I am going to try swapping out the outputs with the ones from the right channel to check if maudio's point about possible fakes could be it first. Assuming the same behaviour occurs, i will take all these measurements tomorrow and post them. Thank you.
As a precaution also replace both C421 and C422, as these will degrade badly.
Nonpolar Nichicon UES are best, chosen with a higher voltage rating if possible.
Nonpolar Nichicon UES are best, chosen with a higher voltage rating if possible.
Are you opening the solder-bridge that shunts R461 for bias current measurement? 0.2mV across R implies only 0.2mA flowing through output transistors. Why are they hot then? A quandry.
Would you report voltages on both sides of relay contacts at emitters of output transistors? And b,e,c of Q403?
Would you report voltages on both sides of relay contacts at emitters of output transistors? And b,e,c of Q403?
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Until now I haven't use a bulb test on this amp.
Best way for troubleshooting on this (but also various other) model needed to perform steps as follow:
1) remove Q411, Q413, Q415, Q417 completely
2) introduce additional 500R potentiometer in series to R453 for the possibility of bias adjust and reduce R453 to 82R-100R
3) Introducing emitter resistors (0R5 or 0R47, low inductance) in series to emitters of Q415 and Q417
3) shorting Main in to GND
4) remove R439 from emitters Q415, Q417 (before BK1) and R441 from speaker output (behind BK-1) and connect both with node C, Q409/R449
easiest way therefore is temporarily replace BK-1 by a silver wire and from there additional wire to node C, Q409/R449.
If later speakers are connected in this condition only VAS stage drive the speakers.
In this mode you are able to check out, whether DC conditions are correct or not (without connected speakers). BIAS range is now easy to investigate on the node R453/455/E, Q409 node C, Q409/R449 rotate of 500R potentiometer. Good range is a value between 2VDC and 3,5VDC. Before doing this check out the DC-conditions of the whole power amp front end and adjust on VR401 the node C, Q409/R449 to 0V +/-20mV max. When doing so, refer to the values of the other channel, which operate correctly.
If all DC values in the right matter and even bias variation range you can connect the speaker to check, if signal is present in very low but undistorted level (remove main in short and volume control minimally turned up).
Next step is to split R459 (2x270R) for connect to speaker output and put in Q411 and Q413 so as remove wire to node C, Q409/R449.
Variation of bias should be between 0V3 and 1V on each 270R resistor. Adjust of the lowest bias value. Adjust VR401 to 0V at output again. On the speaker is the undistorted level a bit louder as before (nevertheless volume control only minimally turned up).
Check out with scope, if unwanted oscillation is present. If not, put in Q415/417 so as BK-1 after remove silver wire and set idle current first of all (to check correct operation) with 500R potentiometer to 10-15mA (10-15mV between emitters of Q415/417). When thermal stability is verified, the quiescent current through the ouput power devices can be increased to about 30mA.
Maybe I have overlooked something in this description because my last troubleshooting on this model is a few years ago.
I've been doing this for a long time with all push-pull amplifiers. This avoids the new parts going up in smoke right away.
Only order the TO-3 transistors from suppliers who know exactly that they come from Onsemi (there are many counterfeits/fakes/copies with different parameters - good known for various problems after repair work. Profusion - go to
https://www.profusionplc.com/de/type/transistor
and rs components are good suppliers therefore.
Additional threads to this integrated amplifier
https://www.diyaudio.com/community/threads/problem-with-a-nad-3130.125788/
https://www.diyaudio.com/community/threads/nad-3130-what-a-mess.383173/
https://www.diyaudio.com/community/threads/nad-3130-rebuilding.365913/
https://www.diyaudio.com/community/threads/nad-3130-sudden-resistor-failure.372693/
https://www.diyaudio.com/community/threads/nad-3130-blowing-fuses.368890/
https://www.diyaudio.com/community/threads/problem-with-a-nad-3130.125788/
P.S.: this model is in order of sound quality my favorite integrated amplifier of those with small idle current (30mA) through the output stage - maybe due the very special (unusual) front end of power amp. Increasing of sound quality you will get by bypassing the preamp (except volume control).
Best way for troubleshooting on this (but also various other) model needed to perform steps as follow:
1) remove Q411, Q413, Q415, Q417 completely
2) introduce additional 500R potentiometer in series to R453 for the possibility of bias adjust and reduce R453 to 82R-100R
3) Introducing emitter resistors (0R5 or 0R47, low inductance) in series to emitters of Q415 and Q417
3) shorting Main in to GND
4) remove R439 from emitters Q415, Q417 (before BK1) and R441 from speaker output (behind BK-1) and connect both with node C, Q409/R449
easiest way therefore is temporarily replace BK-1 by a silver wire and from there additional wire to node C, Q409/R449.
If later speakers are connected in this condition only VAS stage drive the speakers.
In this mode you are able to check out, whether DC conditions are correct or not (without connected speakers). BIAS range is now easy to investigate on the node R453/455/E, Q409 node C, Q409/R449 rotate of 500R potentiometer. Good range is a value between 2VDC and 3,5VDC. Before doing this check out the DC-conditions of the whole power amp front end and adjust on VR401 the node C, Q409/R449 to 0V +/-20mV max. When doing so, refer to the values of the other channel, which operate correctly.
If all DC values in the right matter and even bias variation range you can connect the speaker to check, if signal is present in very low but undistorted level (remove main in short and volume control minimally turned up).
Next step is to split R459 (2x270R) for connect to speaker output and put in Q411 and Q413 so as remove wire to node C, Q409/R449.
Variation of bias should be between 0V3 and 1V on each 270R resistor. Adjust of the lowest bias value. Adjust VR401 to 0V at output again. On the speaker is the undistorted level a bit louder as before (nevertheless volume control only minimally turned up).
Check out with scope, if unwanted oscillation is present. If not, put in Q415/417 so as BK-1 after remove silver wire and set idle current first of all (to check correct operation) with 500R potentiometer to 10-15mA (10-15mV between emitters of Q415/417). When thermal stability is verified, the quiescent current through the ouput power devices can be increased to about 30mA.
Maybe I have overlooked something in this description because my last troubleshooting on this model is a few years ago.
I've been doing this for a long time with all push-pull amplifiers. This avoids the new parts going up in smoke right away.
Only order the TO-3 transistors from suppliers who know exactly that they come from Onsemi (there are many counterfeits/fakes/copies with different parameters - good known for various problems after repair work. Profusion - go to
https://www.profusionplc.com/de/type/transistor
and rs components are good suppliers therefore.
Additional threads to this integrated amplifier
https://www.diyaudio.com/community/threads/problem-with-a-nad-3130.125788/
https://www.diyaudio.com/community/threads/nad-3130-what-a-mess.383173/
https://www.diyaudio.com/community/threads/nad-3130-rebuilding.365913/
https://www.diyaudio.com/community/threads/nad-3130-sudden-resistor-failure.372693/
https://www.diyaudio.com/community/threads/nad-3130-blowing-fuses.368890/
https://www.diyaudio.com/community/threads/problem-with-a-nad-3130.125788/
P.S.: this model is in order of sound quality my favorite integrated amplifier of those with small idle current (30mA) through the output stage - maybe due the very special (unusual) front end of power amp. Increasing of sound quality you will get by bypassing the preamp (except volume control).
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Oh man... I have taken the outputs from the right channel and put them in the left - all problems gone. What an unbelievable waste of time trying to diagnose everything else other than the new outputs :'(. Thank you maudio for the tip!
I couldn't figure out how they were hot with only 0.2mA either, guess it's related to them being fake chips though! I also hadn't opened the solder bridge - i stupidly assumed it would be on the top, so believed mine had been removed by someone else previously. It was, of course done with a blob on the bottom.
Will do! Have already replaced C421
I couldn't figure out how they were hot with only 0.2mA either, guess it's related to them being fake chips though! I also hadn't opened the solder bridge - i stupidly assumed it would be on the top, so believed mine had been removed by someone else previously. It was, of course done with a blob on the bottom.
Thank you for this amazing breakdown of how to do further troubleshooting - genius approach. I will definitely do this if I have any further problems after getting some genuine outputs.
Only buy electronic parts from authorized distributors.
If you value your time, that will be cheaper.
If you value your time, that will be cheaper.
duly noted. Sometimes the shipping fees seem prohibitive when ordering such small quantities
Note:
Digikey has FREE shipping for ANY order, with NO minimum, IF you:
Print out the order with each parts total, your state sales tax, and the grand total.
Enclose a check for the total and mail it to Digikey.
I do this all the time when I only need a few small parts, with no problem.
Digikey has FREE shipping for ANY order, with NO minimum, IF you:
Print out the order with each parts total, your state sales tax, and the grand total.
Enclose a check for the total and mail it to Digikey.
I do this all the time when I only need a few small parts, with no problem.