Hi my NAD 3130 has a defect BD501 causing both 4Amp fuses to blow off. I have been looking for another BD501 with no luck.
Is there a replacement rectifier that will go instead?
Thanks in advance for any reply.
Is there a replacement rectifier that will go instead?
Thanks in advance for any reply.
BD501 is simply the schematic reference code. The schematic says it's a "PBL403" 4A bridge rectifier. KBL04 or GBU4 should work fine. I'd probably fit an 8A rectifier bridge if the original 4A one blew though
You might need to check what caused it to blow ?
Could be something further down stream gone as well ?
Check electrolytics etc.
Could be something further down stream gone as well ?
Check electrolytics etc.
Next step I replaced the BD501 and both fuses ( 4A ) checked the C502/501 for not being shortened. Switched on power and Fuses blow off again immediately. I measured 26 VAC with my Fluke on both fuses with ref to GND - is that correct? Seems to me a little low?
It seems to me strange that both fuses are off. Any good ideas are mostly appreciated.
It seems to me strange that both fuses are off. Any good ideas are mostly appreciated.
It seems that nigelwright's questions should have been investigated.
When a rectifier blows, the problem is a major one, such as a short in the rest of the power supply wiring, the large capacitors or the power amplifier output stage transistors.
Start without power, by verifying the resistance between each DC+ and DC- rail (e.g. across the large capacitor terminals) and common ground. Note the capacitors are already connected between these points and need to be charged with DC in order to measure any amplifier circuit voltages. If there is a very low resistance to ground, you need to find just where it is before applying power and just blowing the fuses again. That's why you should fit a DBT (dim bulb tester or lightbulb limiter) inline, to prevent that while you check circuit voltages to locate the fault.
When there is normal DC power, the rail voltages are less than +/- 30VDC so the AC supply will only be about 22V WRT to ground at full power but higher, like you measure, at about 25VAC when unloaded. NAD3130, 3020 etc. are only low power amplifiers with very small transformers that have poor regulation but still plenty enough for personal entertainment.
When a rectifier blows, the problem is a major one, such as a short in the rest of the power supply wiring, the large capacitors or the power amplifier output stage transistors.
Start without power, by verifying the resistance between each DC+ and DC- rail (e.g. across the large capacitor terminals) and common ground. Note the capacitors are already connected between these points and need to be charged with DC in order to measure any amplifier circuit voltages. If there is a very low resistance to ground, you need to find just where it is before applying power and just blowing the fuses again. That's why you should fit a DBT (dim bulb tester or lightbulb limiter) inline, to prevent that while you check circuit voltages to locate the fault.
When there is normal DC power, the rail voltages are less than +/- 30VDC so the AC supply will only be about 22V WRT to ground at full power but higher, like you measure, at about 25VAC when unloaded. NAD3130, 3020 etc. are only low power amplifiers with very small transformers that have poor regulation but still plenty enough for personal entertainment.
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Thanks a lot for the explanation and advise. I can not measure low resistance to GND from the fuses or across caps, so there might be an issue with one of transistors that will take all power.