I do have electronic background. I have repaired a few transistor amps and built a gainclone.
The NAD S300 manual said the flashing LED means it is in protection mode. I know a few people had the same problem with their S300 amps and they were fixed by NAD for about 60 UK pounds. I am thinking of having a go at the repair myself before I send it to NAD.
Let me know if you have any more advice. Thanks
The NAD S300 manual said the flashing LED means it is in protection mode. I know a few people had the same problem with their S300 amps and they were fixed by NAD for about 60 UK pounds. I am thinking of having a go at the repair myself before I send it to NAD.
Let me know if you have any more advice. Thanks
NAD S300 problem
Hi hifienthusiast.
I have a NAD S300 wich began to have cracking noise on left channel with volume at any level (even in MUTE) and now it has the power led blinking fast.
Did you find the power supply problem?
Can you help?
I have basic electronics knowledge and have been poking inside with a multimeter and found some diferent voltages in a small transistor on each channel... also the amp module for the left channel shows some 40+ voltages on some points and the right channel is at 0.
Thanks.
Hi hifienthusiast.
I have a NAD S300 wich began to have cracking noise on left channel with volume at any level (even in MUTE) and now it has the power led blinking fast.
Did you find the power supply problem?
Can you help?
I have basic electronics knowledge and have been poking inside with a multimeter and found some diferent voltages in a small transistor on each channel... also the amp module for the left channel shows some 40+ voltages on some points and the right channel is at 0.
Thanks.
S300 Repair
I have had the fast blinking lights which indicate that it in protection mode as a result of irregular voltages as a result of a component failure or bad solder joint.
Chances are the ZTX653/753 transistors have overheated and are leaking or a solder joint from top of board to bottom has separated. I resoldered all solder connections in the area of the discoloured circuit board surrounding these transistors and voila it worked again.
I have done the NAD recommended reliability modification via changing out the 4 resistors that allow these transistors to run cooler and more reliable.
These transistors are located on the main board and are the transistors that are grouped together with 8 small TO-92's together for each channel. You will notice the circuit board in this area has discoloured as a result of the excess heat. I have successfully repaired it without changing out the transistors so I conclude that the solder connection went bad as a result of the excess heat. Email me dmullins@cogeco.ca if you need more assitance.
Thanks,
I have had the fast blinking lights which indicate that it in protection mode as a result of irregular voltages as a result of a component failure or bad solder joint.
Chances are the ZTX653/753 transistors have overheated and are leaking or a solder joint from top of board to bottom has separated. I resoldered all solder connections in the area of the discoloured circuit board surrounding these transistors and voila it worked again.
I have done the NAD recommended reliability modification via changing out the 4 resistors that allow these transistors to run cooler and more reliable.
These transistors are located on the main board and are the transistors that are grouped together with 8 small TO-92's together for each channel. You will notice the circuit board in this area has discoloured as a result of the excess heat. I have successfully repaired it without changing out the transistors so I conclude that the solder connection went bad as a result of the excess heat. Email me dmullins@cogeco.ca if you need more assitance.
Thanks,
fjcbs : Re Repair
The channel that measures 40+ volts is the channel at fault as I had the exactly the same problem.... Try resoldering around the transistor where you measured the voltage, then try soldering throughout this area, and finally the transistor replacement.
DO the reliability mod to make it run cooler.... I even added heatsinks on the transistors to draw the heat away from the transistors and circuit board...
Email me for details.. dmullins@cogeco.ca
The channel that measures 40+ volts is the channel at fault as I had the exactly the same problem.... Try resoldering around the transistor where you measured the voltage, then try soldering throughout this area, and finally the transistor replacement.
DO the reliability mod to make it run cooler.... I even added heatsinks on the transistors to draw the heat away from the transistors and circuit board...
Email me for details.. dmullins@cogeco.ca
thanks again dtm1962.
today after work I got home and redid the solder point where you said and my beloved S300 works again!!!
I will try to get some resistors to do the reliability mod and also some heatsinks as you mentioned.
The funny think is that last saturday I went to buy some Kimber 4TC cable to bicable my JMLab speakers with the current 8TC cable I had and as soon as I got home to set the cables connected the amp died! I don't think it was the new cable because the left channel was already making some unordinary noise...
Well, listening to the repaired amp, it sounds much more alive and "fast". Don't know if it is because of the repair job, the new cable or just placebo for me being capable to repair the darn thing all by myself!
today after work I got home and redid the solder point where you said and my beloved S300 works again!!!
I will try to get some resistors to do the reliability mod and also some heatsinks as you mentioned.
The funny think is that last saturday I went to buy some Kimber 4TC cable to bicable my JMLab speakers with the current 8TC cable I had and as soon as I got home to set the cables connected the amp died! I don't think it was the new cable because the left channel was already making some unordinary noise...
Well, listening to the repaired amp, it sounds much more alive and "fast". Don't know if it is because of the repair job, the new cable or just placebo for me being capable to repair the darn thing all by myself!
Good to hear you have fixed it!
Your welcome..... as it is great that we can help each other continue enjoying our beloved hobby!
I bought replacement transistors just in case but .... if it aint broke don't fix it!
Keep an eye on it but I would definitely changed out the resistors (as part of the mod) and add heatsinks for peace of mind!
Your welcome..... as it is great that we can help each other continue enjoying our beloved hobby!
I bought replacement transistors just in case but .... if it aint broke don't fix it!
Keep an eye on it but I would definitely changed out the resistors (as part of the mod) and add heatsinks for peace of mind!
They are not strictly TO92, but rather E-line, which is a package unique to Zetex. E-line offers a higher power dissipation than TO92. However, in quite a few cases where it is used in audio, it still gets too hot and results in failures as in the S300. I fixed my S300's noisy transistors myself, but a few months later it suffered an output short and blew itself up severely. It was eventually repaired and I moved it on as it became impractical when I moved house.
I just finished the recomended mod (switch resistors R311,R313,R312,R314 for 180ohm) and powered the amp and now the sound is very low and all distorted!
I didn't exchange the bias resistors and don't know how (where) to measure bias current - is this the measure of dc offset at the speaker terminals?
I fiddled a bit with the bias pot at the power amp board near R501/R502 but there was no real diference in distortion (just a bit)...
Can someone please give a little help? I've ordered spare transistors but they haven't arrived yet.
aditional note: test points on power amp boards now measure 0v when before they used to measure about 46v... I don't have a variac so I'm afraid of blowing the power stage with to much fiddling on the bias
I didn't exchange the bias resistors and don't know how (where) to measure bias current - is this the measure of dc offset at the speaker terminals?
I fiddled a bit with the bias pot at the power amp board near R501/R502 but there was no real diference in distortion (just a bit)...
Can someone please give a little help? I've ordered spare transistors but they haven't arrived yet.
aditional note: test points on power amp boards now measure 0v when before they used to measure about 46v... I don't have a variac so I'm afraid of blowing the power stage with to much fiddling on the bias
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That's odd, in 2009 you wrote that you have a service manual:
With that manual, you should be able to measure and adjust bias current.
That probably won't cure your problem. Was it working okay before you did the reliablilty mod? If so, go over all the mods and check they're correct.
Yes, I have the manual... Well, it not the full manual, only the schematics and board layout...
The amp worked ok since 2009 when I checked the solder points but last month I was playing a CD and the left channel made a couple of loud pops and the amp went into protection. Since then I just use once again and after about an hour it happend again.
I'm going to recheck the new resistors solders but since it's on both channel I'm not too confident it's a bad mod.
The amp worked ok since 2009 when I checked the solder points but last month I was playing a CD and the left channel made a couple of loud pops and the amp went into protection. Since then I just use once again and after about an hour it happend again.
I'm going to recheck the new resistors solders but since it's on both channel I'm not too confident it's a bad mod.
Ok, I took a chance and replaced the bias resistors R501/R502 as indicated on the MOD instructions. there were 3.9kohm an I replaced with 4.7kohm and now it's sounding fine.
I still don't know how/where to measure the bias current/voltage but the thing as been working non stop for over 2 hours without any glitches. Let's hope it stays like that.
If any kind person could help on where to measure this bias stuff or other reference values for this amp please advise. I would appreciate it greatly
I still don't know how/where to measure the bias current/voltage but the thing as been working non stop for over 2 hours without any glitches. Let's hope it stays like that.
If any kind person could help on where to measure this bias stuff or other reference values for this amp please advise. I would appreciate it greatly
From the service manual available at ElektroTanya | Service manuals and repair tips for electronics experts
ALIGNMENT PROCEDURE
IDLE CURRENT ALIGNMENT (no load, no signal)
1. Connect a digital millivoltmeter between TP301 and TP303, and adjust P501 to obtain a reading of between 30mV and 35mV.
2. Transfer the digital millivoltmeter to TP302 and TP304 and adjust P502 to obtain a reading of between 30mV and 35mV.
3. Leave power on for at least 5 minutes to allow the idle currents to stabilize.
Re-adjust P501 and P502 as necessary to obtain a reading of between 30mV to
35mV on each channel.
ALIGNMENT PROCEDURE
IDLE CURRENT ALIGNMENT (no load, no signal)
1. Connect a digital millivoltmeter between TP301 and TP303, and adjust P501 to obtain a reading of between 30mV and 35mV.
2. Transfer the digital millivoltmeter to TP302 and TP304 and adjust P502 to obtain a reading of between 30mV and 35mV.
3. Leave power on for at least 5 minutes to allow the idle currents to stabilize.
Re-adjust P501 and P502 as necessary to obtain a reading of between 30mV to
35mV on each channel.
My guess is that the loud pops were caused by DC (intermittently) appearing on the output. I would expect a bad solder joint that has recently cracked. Handling the board while applying the mods might temporarily have "cured" the problem, but it will probably reappear in time.
Since this amp has been known to have cracked solder joints, my advice would be to resolder all joints, or at least those that are thermally stressed.
Since this amp has been known to have cracked solder joints, my advice would be to resolder all joints, or at least those that are thermally stressed.
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Thank you Bill_P. With your help I was able to adjust the bias current to spec.
Its was a little difficult to bring both channels to similar values as they bounce up and down.
I also downloaded the full service manual from the link on your tip.
I was not aware of this free stuff. This is not my main hobby - I'm just handy with a soldering iron and have some electronics knowledge from college but no hardcore experience (Electronics gone Computers)
Thanks jitter. That is my experience also. Every time the amp fails (I have since 2002) I believe it is due to overeat and expanding/failing solder joints. Yesterday, while I had it open to do the resistor changes I redid some of the critical areas (again) and I'm hoping it will be fine now (at least for a while). Yesterday night I had it running for about 5 hours without failures.
Since I ordered spare transistors for replacement, if the thing fails again I can change some of them and properly redo their solders.
I don't want (can't afford) to buy another amp and would like to extend this one's life for as long as possible since I enjoy its cozy sound.
Also I don't believe my apartment's sound response deserves anything really better. I think it would be wasted in the not that great sounding living room But that's another story...
Its was a little difficult to bring both channels to similar values as they bounce up and down.
I also downloaded the full service manual from the link on your tip.
I was not aware of this free stuff. This is not my main hobby - I'm just handy with a soldering iron and have some electronics knowledge from college but no hardcore experience (Electronics gone Computers)
Thanks jitter. That is my experience also. Every time the amp fails (I have since 2002) I believe it is due to overeat and expanding/failing solder joints. Yesterday, while I had it open to do the resistor changes I redid some of the critical areas (again) and I'm hoping it will be fine now (at least for a while). Yesterday night I had it running for about 5 hours without failures.
Since I ordered spare transistors for replacement, if the thing fails again I can change some of them and properly redo their solders.
I don't want (can't afford) to buy another amp and would like to extend this one's life for as long as possible since I enjoy its cozy sound.
Also I don't believe my apartment's sound response deserves anything really better. I think it would be wasted in the not that great sounding living room
But that's another story...