Mackie SWA1501

[SVDJ]

Thanks Mark, I have one of these so might change it, although no obvious shorts on U2.
Stranger thing is if i unplug the input board the following happens
-15-SW returns
+15_SW falls to 11.5v
+ and - 15v both measure ok but D16 does not come on. I'm guessing i might still have bad silicon.
I'm guessing with the input board unplugged the 15 v rails should still measure 15v

[SVDJ]

Ok The more i look the more i find.
Q4 blown
Track between R43 and Q14 blown.
Both these repaired / replaced and still got 20v on the speaker J1 and D16 not on
Just found R63 and R64 open cct which i hope answers this and will replace these in the morning along with Q18. Fingers crossed that should be the end of it as i could really do with this up and running by the weekend !!

[MarkusBass]

Ok The more i look the more i find.
Q4 blown
Track between R43 and Q14 blown.

I had two tracks blown; one on the bottom of the board and one on the top (below resistors - difficult to notice but still possible). Someone already mentioned checking the board carefully before powering it up. I think it was you .

Mark

[Bigdrums]

Similar Problem

R63 2.2 ohm .5w
R64 56 ohm
R72 330 ohm

R72 drops to a zener with filter - D45, C34 paralleled Check them for shorts. +15 supply

R73 serves the -15v rail with D46, C32. Just for refernce.

I have a similar problem except voltages are 14.95/-15.16 in that location, (should be good) but just above it on the schematic at D17 reads 16.3, and at D18 -9.25. I checked zenors D17/D18 they look OK, and C15/C16 are not shorted either. The 16.3, -9.25 change slightly when the input board is disconnected, to 16.0/-10.25. Where else should I look?

[RobbieM]

Hi

I recently had one of my Swa1501's out on hire and it returned faulty with a blown 4A fuse. The fuse on the amp board is fine.
On speaking to the hirer, I can only come to the conclusion that they had unplugged the audio input, turned the mixer up to full then plugged the audio back in, causing a surge.
On closer look at the main board I noticed that R64 had been burnt out with scoaring to R63.
Further testing using a DMM found that Q18, Q17, D29, D28, & D40 are blown. I have tried testing capacitors but are getting mixed results with the meter.

As I'm no expert and can only basically use a DMM, before I power up the unit, can anyone help by telling me if replacing these components should correct the issue or would you consider there to be further faults on the board. If so which other components should I test?

Failed Components:
R63
R64
Q17
Q18
D28
D29
D40

Thanks

[MarkusBass]

I don't think that you need to test capacitors. All the problems that were listed in this thread are: blown semiconductors, failed resistors, vaporized tracks. Are you saying that you checked all the tracks and they are OK? I think I had more failed components but after replacing them I powered up the unit (using a bulb in series with the mains supply) and everything was OK (except the speaker, which was also blown). And I also used DMM to fix the amp (and a magnifying glass). Have you checked all transistors and diodes?

Mark

[RobbieM]

I don't think that you need to test capacitors. All the problems that were listed in this thread are: blown semiconductors, failed resistors, vaporized tracks. Are you saying that you checked all the tracks and they are OK? I think I had more failed components but after replacing them I powered up the unit (using a bulb in series with the mains supply) and everything was OK (except the speaker, which was also blown). And I also used DMM to fix the amp (and a magnifying glass). Have you checked all transistors and diodes?

Mark

Hi Markus, yes, I cant see any damage to any of the tracks, I have checked all the Trannys and diodes in the area, having removed a few others from the board to check them, but I did not find any other failures. I'm just concerned that something before or further donw the line may catch me out.........

[Enzo]

There is that hole in the board middle for the heat sink parts. I test every semiconductor hanging into that space. Towards the filter caps, the FETs, and towards the preamp the outputs and drivers. Over in the corner near the preamp connector are a coulpe zener supplies, check them. and down near the opposite corner, but inboard of the large caps, is the other pair of zener supplies, check those. And on the board between the hole adn the preamp side, are those small transistors with the 56 ohm resistors and stuff, check all those. And don't leave out the resistors. They usually burn open when the transistors fail. And along the board edge near the filter caps is the 8-leg IC for that esxtra HV supply. Check the resistors for it and the associated MOSFET. The IC is usually good. Usually.

If you find yourself replacing for example four of five transistors in a circuit, just go ahead and replace the "good" one too. It may not have failed, but it probably was stressed.

I do all that before I even start to troubleshoot.

[MarkusBass]

Hi Markus, yes, I cant see any damage to any of the tracks, I have checked all the Trannys and diodes in the area, having removed a few others from the board to check them, but I did not find any other failures. I'm just concerned that something before or further donw the line may catch me out.........

I think that no one can guarantee here that you did it correctly. I wouldn't be able to do this even if I looked at the amp personally. Especially that you say that you checked all semiconductors in the area (what area?). I had shorted transistors and diodes all over the board (not only on the heatsink). I had 4 tracks vaporized. Several resistors were open but several other had different resistance than before the failure (e.g. 137 Ohms instead of 470 Ohms). So you have to check the board really good. When you do it, power it up using a light bulb and see if it works. You cannot do anything more. If it does not work, it means that you haven't identified all parts that failed and you have to do it once again.

Mark

[Bigdrums]

I have 3 questions regarding these troublesome subs:

1) at D35, the high voltage rectifier-shouldn't I measure +70V / -70V referenced to common ground?

2) if so and mine is not, measuring the impedance between the + and - rectifier output terminals to common ground should be nearly equal, correct?

3) what would cause one of the green LED's, D16 not to light up like it's counterpart D15?

4) what are the indicated functions of the 5 LED's- D15, D16, D34, D42, and D44?

Thanks for any replys!

[RobbieM]

There is that hole in the board middle for the heat sink parts. I test every semiconductor hanging into that space. Towards the filter caps, the FETs, and towards the preamp the outputs and drivers. Over in the corner near the preamp connector are a coulpe zener supplies, check them. and down near the opposite corner, but inboard of the large caps, is the other pair of zener supplies, check those. And on the board between the hole adn the preamp side, are those small transistors with the 56 ohm resistors and stuff, check all those. And don't leave out the resistors. They usually burn open when the transistors fail. And along the board edge near the filter caps is the 8-leg IC for that esxtra HV supply. Check the resistors for it and the associated MOSFET. The IC is usually good. Usually.

If you find yourself replacing for example four of five transistors in a circuit, just go ahead and replace the "good" one too. It may not have failed, but it probably was stressed.

I do all that before I even start to troubleshoot.

Thanks for this I have tested all the other zeners which seem to be ok, I have found that the Mosfet's are blown as well, how would I go about testing the IC? I have found the diagram for it online but have no idea how to go about it. Also you metioned the smaller transistors and resistors, will these all need to be removed like the larger transistors to test or can they be done on the board? Also the large Diodes around the power supply area, would these need to be lifted aswell?
Thanks
http://www.datasheetcatalog.org/data.../HCPL-3100.pdf

[Enzo]

Well, all that was a general approach, when I find a part reads as shorted, it has to come out. I can then test it again. Usually it is bad, but once in a while the short is parallel to tthe part and still on the board. I look at it this way. Parallel shorts on teh board can make a transistor appear shorted een when it is not. But there is nothing in the world in a circuit that can make a shorted transistor look not shorted, y'know?

I am mainly looking for shorted components. SO I don;t often lift the parts first, unless they measure short.

And the small transistors? If they pass the junction drop test while in circuit, I usually leave them alone until variac time. Just stay aware that many of the parts are connected together, so if you find a shorted output transistor, it can make a good driver look shorted. SO clip out bad parts as soon as you find them.

You mean the IC for that auxilliary high voltage supply? It usually is not bad, but I can check if for shorts between pins that ought not be that way. And it depends upon what parts around it were blown up.

[RobbieM]

Thanks for your help with this, after replacing all the transistors on the heatsink, the diodes and the resistors as originally stated, the amp seems to be working again. The only issue I discovered was that on a quick check of the driver before connecting, I found it to be reading zero, so that is now off in the post to Wembley Loud speakers for repair.

My last question is that there are 4 green LEDs on the board, D15 & D16 are lit, I assume these are to show the power supply is healthy?. D44 & 42 are not lit, but from the diagram I guess these are only lit when the preamp is driving? Can someone enlighten me please! Thnaks

[MarkusBass]

My last question is that there are 4 green LEDs on the board, D15 & D16 are lit, I assume these are to show the power supply is healthy?.

They provide constant voltage for current sources on the input of the power amp. But since they are supplied directly from +/-15V rails, you may say that they show healthy power supplies.

D44 & 42 are not lit, but from the diagram I guess these are only lit when the preamp is driving? Can someone enlighten me please! Thnaks

Yes, that's correct.

Mark

[jermandubber]

Hello all,

Brand new to the board and have read through this thread as thoroughly as possible. I work for a live music venue that owns 2 of these subs, neither of which work right now. both have blown what I believe to be the F1 7a 250V fuse. In one, I have replaced the fuse 2 times and both times, it blew with a flash of light immediately upon power up. In the other, it worked for about a week and blew again.
I have no real world electronic experience, but my venue believes it would be cheaper to have me learn to fix them instead of bringing them to a shop. I think they are stupid, but I also appreciate the opportunity to learn while getting paid.

If you guys could help me start to trouble shoot this issue, I would much appreciate it.

I am going to start on the checklist of known issues with this amp I saw earlier in the thread. I also checked the ohm reading for the speaker cables at the ends that connect to the power amp and got a reading of 9.5... is that strange due to it being a 12 ohm speaker?