Initially the unit was dead. Various caps & a few resistors were either dead or out of spec. Got it going & since have done a complete recap & Bourns trimpots.
Let me tell you it REALLY sounds great.
The final "issue" is Q507 & Q508 get really hot. I know these 2 have a reputation for running hot, but too hot to touch? They used to have a tiny bit of metal attached as a heatsink, which I have since replaced with a proper aluminium sink. But still too hot to touch. I've had them out before/during/& after, they test ok with DMM.
A lot of the initially dead etc bits were from this section. R519 a 5K6 resistor was 8.9Mohms, C523, C518/9 were dead.
View attachment Nad 3020i Circuit Diagram only.pdf
I hope someone can either tell me this is normal, or guide me to a fix. Replacements of a preferred brand are not readily/cheaply available, so for me this is not a replace & try situation.
Looking forward to your comments.
Let me tell you it REALLY sounds great.
The final "issue" is Q507 & Q508 get really hot. I know these 2 have a reputation for running hot, but too hot to touch? They used to have a tiny bit of metal attached as a heatsink, which I have since replaced with a proper aluminium sink. But still too hot to touch. I've had them out before/during/& after, they test ok with DMM.
A lot of the initially dead etc bits were from this section. R519 a 5K6 resistor was 8.9Mohms, C523, C518/9 were dead.
View attachment Nad 3020i Circuit Diagram only.pdf
I hope someone can either tell me this is normal, or guide me to a fix. Replacements of a preferred brand are not readily/cheaply available, so for me this is not a replace & try situation.
Looking forward to your comments.
Those are series pass regulators and it looks like they will run hot. They certainly shouldn't sizzle water but may well be to hot touch as you have found. Sadly that kind of design is typical in many products and if you are in a hot climate... well that puts even more stress on the design.
Also, something you probably don't want to hear but I'll mention it... those particular type of transistors from that era have a habit of failing intermittently open circuit base to emitter. Why that should be I have no idea but I've seen it many times on older TV's and so on. Just something to be aware of.
Also, something you probably don't want to hear but I'll mention it... those particular type of transistors from that era have a habit of failing intermittently open circuit base to emitter. Why that should be I have no idea but I've seen it many times on older TV's and so on. Just something to be aware of.
The voltage out from the those regulated supplies isn't equal either. The + rail is +50V in, and +43V out from Q507. The negative rail is -50Vin, -28V out from Q508.
The +43V rail is for the front end supply of the power amps but must be quite a heavy load compared to typical 3 stage designs where about 12 mA each amplifier is enough. I would have thought the +28V preamp supply was largely handled by the BD139 (Q511) yet there's no heatsink, so for interest, what are the actual currents in those regulator transistors - as measured across series resistors R511,512?
As Mooly hints, they do get uncomfortably hot but unless they sizzle with a wet finger, they should be Ok for a reasonable transistor lifetime. Translating that into degrees C may be a bit difficult but right now, its about 4 degrees outside which makes any powered transistor feel warm.
The +43V rail is for the front end supply of the power amps but must be quite a heavy load compared to typical 3 stage designs where about 12 mA each amplifier is enough. I would have thought the +28V preamp supply was largely handled by the BD139 (Q511) yet there's no heatsink, so for interest, what are the actual currents in those regulator transistors - as measured across series resistors R511,512?
As Mooly hints, they do get uncomfortably hot but unless they sizzle with a wet finger, they should be Ok for a reasonable transistor lifetime. Translating that into degrees C may be a bit difficult but right now, its about 4 degrees outside which makes any powered transistor feel warm.
Thanks to you both. How do you guys know soooo much, and so readily impart your time & knowledge.
R511 0.050
R512 0.053
Q507 you cannot keep touching it is that hot. Q508 is bearable. Nothing else (that I dare touch) is even remotely warm. Ambient is 19C.
Cheers
Tony
so for interest, what are the actual currents in those regulator transistors - as measured across series resistors R511,512?
R511 0.050
R512 0.053
Q507 you cannot keep touching it is that hot. Q508 is bearable. Nothing else (that I dare touch) is even remotely warm. Ambient is 19C.
Cheers
Tony
I've got the same problem here. It's so hot that it melt the soldering under it. Have you figured out what is the problem? I've attached a big heatsink to it but still no luck-can't even touch it. The closest transistor is hot too but not that hot to boil the water on it.
When I got my NAD one month ago - there was a problem with FM (it worked only below 90 Mhz). So I replaced a burned Zener diode (D513). All worked fine. then I replaced old capacitors:
c526
c525
c522
c524
c516
c519
c518
c523
c517
d512 diode
d513 diode
С321
С322
C325
C326
С401
С402
С409
С410
С415
C416
С427
С428
С508
С509
С531
С601
С603
After that I tested old capacitors and found that their capacity is good and time didn't affect them. So i decided not to replace all other caps in this AMP.
But found a hot Q508. But the reason is not new caps, because before a caps replacement I saw a dark field on the back side of a printed circuit board, what means it was hot for a long time....
This week I will show my NAD to a guy who is a good hand in all these electronics.
I will let you know...
And buy the way another small problem:
When the tuner is tuned to a station, I switch the amp to a CD or Video input (and nothing connected to these inputs). I turn the high volume and I hear the FM station a little bit... Also if I have something connected to CD input, I hear it a little bit when the AMP is on the video....
When I got my NAD one month ago - there was a problem with FM (it worked only below 90 Mhz). So I replaced a burned Zener diode (D513). All worked fine. then I replaced old capacitors:
c526
c525
c522
c524
c516
c519
c518
c523
c517
d512 diode
d513 diode
С321
С322
C325
C326
С401
С402
С409
С410
С415
C416
С427
С428
С508
С509
С531
С601
С603
After that I tested old capacitors and found that their capacity is good and time didn't affect them. So i decided not to replace all other caps in this AMP.
But found a hot Q508. But the reason is not new caps, because before a caps replacement I saw a dark field on the back side of a printed circuit board, what means it was hot for a long time....
This week I will show my NAD to a guy who is a good hand in all these electronics.
I will let you know...
And buy the way another small problem:
When the tuner is tuned to a station, I switch the amp to a CD or Video input (and nothing connected to these inputs). I turn the high volume and I hear the FM station a little bit... Also if I have something connected to CD input, I hear it a little bit when the AMP is on the video....
There are several recent posts about heat from the +ve preamp power supply regulator transistor, Q507. You will have read in another current thread that they reach about 60C normally and yes, this is too hot to hold for longer than a few seconds. Don't assume because you can't hold the one constantly hot transistor that it is not normal though. Still, anything above 70C in this model, should really be corrected.
If you are as serious as suggesting the temperature of the transistor, even on its heatsink, can melt its solder, the transistor must have already failed. Perhaps you exaggerate a bit. Q507 powers the input circuits (front end) of the power amplifiers with +43V and you can compare with voltages shown on the power amplifier schematic and determine how much current flows to where by also measuring voltage across any series resistor in the path to each channel amp. at say, R425,326,437,438. Calculate and compare current in either channel to each section by using Ohm's law - I=E/R.
A schematic is linked in this thread
but a better copy is here: NAD 3020 Manual - Stereo Integrated Amplifier - HiFi Engine
How about a bit more factual investigation and measure with any cheap thermocouple meter probe or handheld IR thermometer, just how hot you really mean. Then you'll know whether this is quite normal or you all have chanced on the same new problem.
The schematic in the service manual shows expected voltages in the relevant regulator circuits for Q507,8. Check the voltages carefully by not slipping with dangerous blunt or rounded meter probes and destroying anything further. If there is a problem, the regulator output voltages (+43, +28, -28) will be low and the corresponding +43 and 42V readings in the amplifier front ends will be low too. Look how this all boils down to the load on the regulator transistor. The more the load current, the hotter it gets, so you look for shorts and increased loads due to ageing or changes made.
I see on another forum that 2 guys have been messing with other parts of their amplifiers and getting into big trouble with shorts and low value resistors, so it's hard to tell what is really going on with your restoration work but there are many threads here on the same 3020 sagas. Many others have already fallen into the same traps and asked for help. It might be quicker to look at those many other various 3020 model threads too.
If you are as serious as suggesting the temperature of the transistor, even on its heatsink, can melt its solder, the transistor must have already failed. Perhaps you exaggerate a bit. Q507 powers the input circuits (front end) of the power amplifiers with +43V and you can compare with voltages shown on the power amplifier schematic and determine how much current flows to where by also measuring voltage across any series resistor in the path to each channel amp. at say, R425,326,437,438. Calculate and compare current in either channel to each section by using Ohm's law - I=E/R.
A schematic is linked in this thread
but a better copy is here: NAD 3020 Manual - Stereo Integrated Amplifier - HiFi Engine
How about a bit more factual investigation and measure with any cheap thermocouple meter probe or handheld IR thermometer, just how hot you really mean. Then you'll know whether this is quite normal or you all have chanced on the same new problem.
The schematic in the service manual shows expected voltages in the relevant regulator circuits for Q507,8. Check the voltages carefully by not slipping with dangerous blunt or rounded meter probes and destroying anything further. If there is a problem, the regulator output voltages (+43, +28, -28) will be low and the corresponding +43 and 42V readings in the amplifier front ends will be low too. Look how this all boils down to the load on the regulator transistor. The more the load current, the hotter it gets, so you look for shorts and increased loads due to ageing or changes made.
I see on another forum that 2 guys have been messing with other parts of their amplifiers and getting into big trouble with shorts and low value resistors, so it's hard to tell what is really going on with your restoration work but there are many threads here on the same 3020 sagas. Many others have already fallen into the same traps and asked for help. It might be quicker to look at those many other various 3020 model threads too.
I have a nad 3020i and it is normal that the transistor warmer, look at the pictures:
http://i57.tinypic.com/wknt77.jpg
http://i60.tinypic.com/2vxj31v.jpg
http://i57.tinypic.com/wknt77.jpg
http://i60.tinypic.com/2vxj31v.jpg
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