I was wrong stating what the 2 small To92 transistors did. One power fet is controlled directly from the second op-amp. The negative power fet is controlled by both the To92 transistors since the gate is at least negative 50 volts. It looks like the 4 diodes on the base of the output transistors are there to stop the base emitter voltage going over 4 volts.
I have a pair of these subs and one of them shat it's self,long story short I took it to 4 repair shops and wouldn't touch it but eventually found a guy not far away from me took a look at it and was quite confident he could sort it he had to send away for some parts.after watching this video it seems a very over complicated amp but they do work very well
Thank you for your comment. The way I see it is, only one of his two sub woofers failed. If He had a rack mounted amp failure, He’d lose all his sound, or maybe just one channel if He was lucky. Always a difficult topic between rack mounted amps and active speakers and subs.
Wow, this is terrific. I googled to learn more about the sub when you mentioned "disco" and so yes, it is used for professional sound applications (116dB!), and it would seem quite a few people prefer its sound over other brands using 15" drivers but that the amplifiers in them are problematic.
Thank you for your comments. The owner of this sub can't remember how many years ago this amp was repaired, nor can I lol. I asked how often the sub was used. He said 4 to 5 times a month, every month of each year. His two subs both worked at the last event, this amp in the video did not work when He switched it on at another event. I believe the failing FET transistor caused the rest to fail. (The fet with the noise on scope) I think this amp should last a few more years. Great amps if used sensibly. Great schematics and all electronic parts available. Oh, nearly forgot, there is now this video to help with repairs. These parts are about £20 for all of them.
Thank you John B for sharing your detailed troubleshooting analysis for this Mackie SWA-1501. Very helpful and professional approach. Thank you I have the same Mackie SWA-1501 with some issues.. With your help and advice i will try to analyse it's fault.
HI I have the same subwoofer. It suddenly stopped working . so im guessing something to do with the fuse . I took it out it was bigger than normal fuses but now i cant find it. I have the code. but am also strugggling to find online or in shops. The fuse number I have is F63AL250V. Is this what you were using ? thanks
Why had the components failed to begin with before people started to replace incorrect resistors etc. Great video, you managed to go nearly a whole hour without tapping components on the board with your biro. haha. Also, safety first, when you blew the 3am mains fuse could you have got a shock off the board?
The million dollar question, why do parts fail. The age of a component can cause failure, especially with FET transistors. The FETs can suffer from gate erosion causing them to fail. I think this amplifier might be driving a woofer that is going short circuit and drawing too much current. Generally, in a class B amplifier, if one part fails, it causes excess current to flow which in turn causes other parts to fail.
Important service Bulletin Re SWA1501 Affected Products SWA 1501 [All serial numbers] Failure Description SWA 1501 amplifier section, failing multiple times in short timeframes. Units fail to pass signal and sometimes actually emit smoke. Cause The misprinting of reference designators D19 (zener diode P/N: 82131050) and D20 (BAV21 diode P/N: 82112002) on the printed circuit board causes the problem, as the two locations numbers are swapped on the silkscreen. The correct components are being oriented correctly, but end up being in the wrong place. The picture below is an example of the INCORRECT silk screen. The CORRECT silkscreen sequence will be: R27, R28, R29, D19, D20, R30, D21 etc.. Action When an SWA 1501 is being repaired for any reason, please look at the amplifier assembly and specifically at locations D19 and D20. If the locations are reversed from the schematics, install zener diode P/N: 82131050 in D20 and install BAV21 diode P/N: 82112002 in D19. Simplification The location next to R29 should have the Zener diode P/N: 82131050 installed. The location next to R30 should have the BAV21 diode P/N: 82112002 installed. Orientations are indicated by the silk screen, as this is correct.
I was wrong stating what the 2 small To92 transistors did.
One power fet is controlled directly from the second op-amp. The negative power fet is controlled by both the To92 transistors since the gate is at least negative 50 volts.
It looks like the 4 diodes on the base of the output transistors are there to stop the base emitter voltage going over 4 volts.
I have a pair of these subs and one of them shat it's self,long story short I took it to 4 repair shops and wouldn't touch it but eventually found a guy not far away from me took a look at it and was quite confident he could sort it he had to send away for some parts.after watching this video it seems a very over complicated amp but they do work very well
Nothing beats an old school outboard & amp rack.
Thank you for your comment.
The way I see it is, only one of his two sub woofers failed.
If He had a rack mounted amp failure, He’d lose all his sound, or maybe just one channel if He was lucky.
Always a difficult topic between rack mounted amps and active speakers and subs.
Wow, this is terrific. I googled to learn more about the sub when you mentioned "disco" and so yes, it is used for professional sound applications (116dB!), and it would seem quite a few people prefer its sound over other brands using 15" drivers but that the amplifiers in them are problematic.
Thank you for your comments.
The owner of this sub can't remember how many years ago this amp was repaired, nor can I lol.
I asked how often the sub was used.
He said 4 to 5 times a month, every month of each year.
His two subs both worked at the last event, this amp in the video did not work when He switched it on at another event.
I believe the failing FET transistor caused the rest to fail. (The fet with the noise on scope)
I think this amp should last a few more years.
Great amps if used sensibly.
Great schematics and all electronic parts available.
Oh, nearly forgot, there is now this video to help with repairs.
These parts are about £20 for all of them.
@@JohnB-2021 oh failing FET.
Thank you John B for sharing your detailed troubleshooting analysis for this Mackie SWA-1501. Very helpful and professional approach. Thank you
I have the same Mackie SWA-1501 with some issues.. With your help and advice i will try to analyse it's fault.
Thank you for your kind comments
Be sure to read the new comment by @magnum07546 posted 11/12/2023
Excellent
Thank you very much.
HI I have the same subwoofer. It suddenly stopped working . so im guessing something to do with the fuse . I took it out it was bigger than normal fuses but now i cant find it. I have the code. but am also strugggling to find online or in shops. The fuse number I have is F63AL250V. Is this what you were using ? thanks
On the main board there should be a 1 amp fuse and an 8 amp fuse.
On the transformer panel, there should be a 4 amp fuse for UK use.
Another great video!
Thank you kind sir.
Why had the components failed to begin with before people started to replace incorrect resistors etc. Great video, you managed to go nearly a whole hour without tapping components on the board with your biro. haha. Also, safety first, when you blew the 3am mains fuse could you have got a shock off the board?
The million dollar question, why do parts fail.
The age of a component can cause failure, especially with FET transistors.
The FETs can suffer from gate erosion causing them to fail.
I think this amplifier might be driving a woofer that is going short circuit and drawing too much current.
Generally, in a class B amplifier, if one part fails, it causes excess current to flow which in turn causes other parts to fail.
Important service Bulletin Re SWA1501
Affected Products
SWA 1501 [All serial numbers]
Failure Description
SWA 1501 amplifier section, failing multiple times in short timeframes. Units fail to pass signal and sometimes actually emit smoke.
Cause
The misprinting of reference designators D19 (zener diode P/N: 82131050) and D20 (BAV21 diode P/N: 82112002) on the printed circuit board causes the problem, as the two locations numbers are swapped on the silkscreen. The correct components are being oriented correctly, but end up being in the wrong place. The picture below is an example of the INCORRECT silk screen. The CORRECT silkscreen sequence will be: R27, R28, R29, D19, D20, R30, D21 etc..
Action
When an SWA 1501 is being repaired for any reason, please look at the amplifier assembly and specifically at locations D19 and D20. If the locations are reversed from the schematics, install zener diode P/N: 82131050 in D20 and install BAV21 diode P/N: 82112002 in D19.
Simplification
The location next to R29 should have the Zener diode P/N: 82131050 installed. The location next to R30 should have the BAV21 diode P/N: 82112002 installed. Orientations are indicated by the silk screen, as this is correct.
Wow, thank you for this important information.
I'll be sure to check in the future.
I have a problem with a couple of ELX 118 P modules, could you help me find someone who can repair them?
You can buy the modules on the internet.
Do you repair for anyone? I have 2 swa15 amps that's in need of a repair?
I love in Norway, but if shipping the amps to You would be OK?
Sorry I only repair amps for my friend dj.
@@JohnB-2021 kk, np. I'll have them repaired somehow 😊
What is the real power of this amplifier??
About 300 watts RMS into 12 ohm.
But the manual says 500 wats😢
@@user-ng5fp9mc8x The schematic says 600. That is peak power. You asked for real power.
Thank you)