First and foremost, hey everyone, first time poster. I've lurked a little here and there, and figured I'd go ahead and sign up. I'm in need of a little guidance, if anyone would be so kind as to lend a hand...I'll try and include as much information as possible.
A friend of mine runs shows for a bar/market/venue here in Charlotte, and one of the bands bumped into the mixer after their set and it took a 4-6 foot fall, from what I was told. It wouldn't power on afterwards. I told her I'd take a look at it, but couldn't promise anything.
First thing I did was check the power input jack. No broken solder joints, the ground was good, that all checked out. Next, I checked the fuse (should have done that first - my knowledge is a work in progress) and the fuse was bad. I went ahead and ordered some new fuses and popped one in there. Then I smelled the wonderful smell of overheating electronic components.
A few traces were burnt up, which I've since point-to-pointed (so pro looking.) The thing that I've checked after this is diodes...there are a lot of short circuited diodes around the 5 heat sinks on this thing. At this point I'm in a little over my head, and the most reputable amp tech that I know said he wouldn't wish it upon someone. So I figure this is as good of a place to go as any.
The short of it;
1. Powered mixer dropped 4-6 feet, won't turn on.
2. Power input jack is good, no visibly friend resistors.
3. Fuse was blown. Replaced fuse. Current came through way too hot, burned up a few traces. Have since patched them up w/ wire.
4. Tested all the diodes in the power section of the amp, and it appears that roughly half of them are short circuited (reading similarly in both directions, or positive-to-ground reads substantilly higher than ground-to-positive.)
5. What should I go about doing next? What could have caused the diodes to short circuit like this?
Thanks in advance for any help that you guys can offer!
A friend of mine runs shows for a bar/market/venue here in Charlotte, and one of the bands bumped into the mixer after their set and it took a 4-6 foot fall, from what I was told. It wouldn't power on afterwards. I told her I'd take a look at it, but couldn't promise anything.
First thing I did was check the power input jack. No broken solder joints, the ground was good, that all checked out. Next, I checked the fuse (should have done that first - my knowledge is a work in progress) and the fuse was bad. I went ahead and ordered some new fuses and popped one in there. Then I smelled the wonderful smell of overheating electronic components.
A few traces were burnt up, which I've since point-to-pointed (so pro looking.) The thing that I've checked after this is diodes...there are a lot of short circuited diodes around the 5 heat sinks on this thing. At this point I'm in a little over my head, and the most reputable amp tech that I know said he wouldn't wish it upon someone. So I figure this is as good of a place to go as any.
The short of it;
1. Powered mixer dropped 4-6 feet, won't turn on.
2. Power input jack is good, no visibly friend resistors.
3. Fuse was blown. Replaced fuse. Current came through way too hot, burned up a few traces. Have since patched them up w/ wire.
4. Tested all the diodes in the power section of the amp, and it appears that roughly half of them are short circuited (reading similarly in both directions, or positive-to-ground reads substantilly higher than ground-to-positive.)
5. What should I go about doing next? What could have caused the diodes to short circuit like this?
Thanks in advance for any help that you guys can offer!
Up until this point, most of my work has been on linear power supply amps. Most of the experience I've obtained is through just trial and error, jumping in and seeing what works/doesn't work. Not an exact science, but it's served me well for awhile and I like to learn new things, provided I can access the necessary information. At this point I'm a bit stumped. Had a few things in mind to try, but just wanted a little guidance somebody might have off the top of their head.
I would go to a shop if not for the fact that the owner has stated she'd just junk it if I weren't able to fix it. $300 or-so PA head new, hardly worth putting in $150 to get it fixed when you can buy a used one for around that price, I'd imagine. I'm just trying to help out a friend.
I would go to a shop if not for the fact that the owner has stated she'd just junk it if I weren't able to fix it. $300 or-so PA head new, hardly worth putting in $150 to get it fixed when you can buy a used one for around that price, I'd imagine. I'm just trying to help out a friend.
Trial and error doesn't work with switch-mode (not that I'm sure it really ever worked with linear either
) - faults tend to be catastrophic, with any minor fault blowing bits everywhere.It makes them difficult to repair, because unless you repair it 100% correctly everything blows again when you first power it up.
The fact that it was killed by a fall suggests that something was broken or cracked, and that this caused the PSU to self-destruct.
With no experience I would suggest you steer clear, as you're likely to just produce big heaps of blown components.
Trial and error doesn't work with switch-mode (not that I'm sure it really ever worked with linear either
It makes them difficult to repair, because unless you repair it 100% correctly everything blows again when you first power it up.
The fact that it was killed by a fall suggests that something was broken or cracked, and that this caused the PSU to self-destruct.
With no experience I would suggest you steer clear, as you're likely to just produce big heaps of blown components.
This is good stuff to know! I imagined after my experience with the traces getting burnt up that this was the case, but I wasn't entirely sure. I wish that I had done some more prodding after realizing that the fuse was blown, because now I imagine it'll be extremely difficult to tell what blew during the fall and what blew after I replaced the fuse.
The only reason I'm even entertaining the project anymore is that my friend has told me she'll junk it if I'm unable to get it back up and working...so there's no real consequence here...just opportunity cost of the time, perhaps a couple bucks on components. I consider it a learning experience, even if I fail miserably.
If you have a copy of the schematic, I would appreciate it! And thanks for the information. I realize that it's likely a lost cause, but it's not really costing me much more than time at this point to try, and I know that I'm learning lessons even in failure. So I'm okay with at least entertaining it until I get frustrated and quit. It's fun to get educated...at least sometimes.
I'm going to go ahead and try to check the transformer and filter caps if I can...I've only got a DMM at the time, but was considering investing in a cap meter for future work.
Thanks again for replying, everyone.
Hi !
I am trying to fix that device. After power on - power led turns off after 3 secs.
After disassembly - it looks like it overheated because of filth and dirt blocking the ventilation.
After disconnecting amp module completely, device powers up normally.
All voltages available.
After disassembling amp found one of the power transistors 2SA1386A (Sanken) on one side has a short between base and collector - its the filthy side.
Replaced both SA1386A with same Transistor, different mfgr. (original SANKEN) -now icssemi.
Had to replace glimmer isolators - replaced with silicon mat
Still problem to power on the device if amp connected... somehow looks like the repaired side starts to oscillate after power on...
So amp powers down again after 4 secs.
Measured supply and parts of power supply - as suggested in repair manual ... seems ok.
Could it be the different mfgr of that transistor ?
Or is there something else to consider... tried out different positions for idle current - no change...
rgds - will post in another thread.
I am trying to fix that device. After power on - power led turns off after 3 secs.
After disassembly - it looks like it overheated because of filth and dirt blocking the ventilation.
After disconnecting amp module completely, device powers up normally.
All voltages available.
After disassembling amp found one of the power transistors 2SA1386A (Sanken) on one side has a short between base and collector - its the filthy side.
Replaced both SA1386A with same Transistor, different mfgr. (original SANKEN) -now icssemi.
Had to replace glimmer isolators - replaced with silicon mat
Still problem to power on the device if amp connected... somehow looks like the repaired side starts to oscillate after power on...
So amp powers down again after 4 secs.
Measured supply and parts of power supply - as suggested in repair manual ... seems ok.
Could it be the different mfgr of that transistor ?
Or is there something else to consider... tried out different positions for idle current - no change...
rgds - will post in another thread.
Hi fritz194,
I found a service manual online, too big for attachment, but linked: https://elektrotanya.com/yamaha_emx212s_sm.pdf/download.html#dl
Assuming this is the correct manual, can you steer us toward the area you've identified as suspect? Thanks.
Good luck!
I found a service manual online, too big for attachment, but linked: https://elektrotanya.com/yamaha_emx212s_sm.pdf/download.html#dl
Assuming this is the correct manual, can you steer us toward the area you've identified as suspect? Thanks.
Good luck!