WT800C Meltdown

D

DrEvil

Feb 28, 2023
25
28
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#1
Our bass player has a WT800C amp that he said he thought was running hot. We pulled the cover off to observe as he played it. A few minutes in, there was some pretty spectacular arcing between R27A and the speakon output (on the low out power amp side). Before this lighting show I noticed there was no heat being produced on that side. It seems that the power transistors were not operational beforehand. Checking them afterwards shows shorts between all legs. There are also several spots of heat damage on the board resulting in broken traces. Not sure if all of that is a result of the arcing. What I'm thinking of doing is replacing all burnt components and anything connected to any of the burnt up spots on the board, and bridging the traces with wire.

What I'm wondering is:
can anyone say what might have caused this? Maybe the amp has been run in bi amp and bridged mode at the same time in the past and some components finally failed. Or running bi amp with no load on that side? Or is it possibly an inherent problem with the amp?
Is it possible to get a new circuit board? Eden only deals with authorized service centers for parts like this. Meaning they won't help consumers working on Eden amps. How about recommendations for someone who can make a copy of the board?

Is there any issue using different types of solder together? I've been using Kester 63/37 rosin core. In removing a couple resistors from this board I found that my normal temp setting will barely melt the solder. Using different materials gets me thinking about galvanic reactions, corrosion, and overall bond compatibility.
Many thanks!
20230227_150732.jpg 20230226_160027.jpg
 
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#4
Elektrotanya for electronics experts

Schematic download.

working on the amp is dangerous of course…. Arcing circuits are super dangerous. Don’t do it but for theoretical discussion…

I would try to remove components that isolate “logical” sections for individual testing. Removed components can be tested and those adjacent (since they are next to an open circuit) can be tested using meters.

If the problem section is isolated, the remaining portion can hopefully be tested. If the “good” sections don’t work, the board could be fried (it is obviously toasted already). Only very studious people will want to add wires to route past damaged areas (which you intend to do). Long wires can increase EMI susceptibility. I don’t know if twisted pair wires would help or not. Maybe someone could chime in.


Removing expensive or difficult to obtain components can be good as long as they don’t cause the remaining circuit to go out of control.


I would call a tech at an Eden authorized service center and get the cost of a board swap.
 
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#5
Old Fart said:
Someone may suggest using a troubleshooting procedure first, rather than just replacing some parts and crossing your fingers. The ones with greater experience are often the ones suggesting this.
Click to expand...
Any idea where to learn or get some guidance on this troubleshooting procedure? What I've tried besides testing the transistors and other components: powered it up at low voltage and compared voltages at the power supply connector between the identical high out power amp board. The only difference is in the thermostat section. I think that narrows it down to the power amp board where the damage occurred, unless a faulty bi-amp or bridge switch caused it. I'll have to check those switches. It's unfortunate that I don't know what set this off. If someone said 'I accidentally ran it with both modes switched on' it would be one thing. My friend got the amp recently and it's likely that something's been smoldering since he got it.
 
#6
Dadum said:
Elektrotanya for electronics experts

Schematic download.

working on the amp is dangerous of course…. Arcing circuits are super dangerous. Don’t do it but for theoretical discussion…

I would try to remove components that isolate “logical” sections for individual testing. Removed components can be tested and those adjacent (since they are next to an open circuit) can be tested using meters.

If the problem section is isolated, the remaining portion can hopefully be tested. If the “good” sections don’t work, the board could be fried (it is obviously toasted already). Only very studious people will want to add wires to route past damaged areas (which you intend to do). Long wires can increase EMI susceptibility. I don’t know if twisted pair wires would help or not. Maybe someone could chime in.


Removing expensive or difficult to obtain components can be good as long as they don’t cause the remaining circuit to go out of control.


I would call a tech at an Eden authorized service center and get the cost of a board swap.
Click to expand...

Thanks for the reply. I'm aware of the dangers or working with HV and take proper precautions, thanks for the concern. As far as the repair goes I'm starting to think checking with a service center would be best to try first. As you mentioned there's the chance of adding EMI, and long term reliability is also a concern. If I could get an oem replacement board I'd have no trouble ordering new parts and building a brand new power amp module, but I don't think I can procure one. I've seen some services that will clone boards but then there's the risk of it getting lost in the mail or them making a mistake on it. Yep, we're going to see what they'd charge to deal with it.
 
#7
The very first step in troubleshooting is understanding how the circuit is supposed to work.

From there, diagnostics, measurements and experience identifying the cause of the failure.

Once the cause is determined, the bad parts can be identified (experience about failure modes helps here) and replaced, and other necessary repairs completed.

It is critical to understand how global NFB amplifiers work, because what you think you see may be the opposite of what’s really happening.

A scope, signal generator and good DMM are essential tools, as is a current limited variable AC supply.
 
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#8
agedhorse said:
The very first step in troubleshooting is understanding how the circuit is supposed to work.

From there, diagnostics, measurements and experience identifying the cause of the failure.

Once the cause is determined, the bad parts can be identified (experience about failure modes helps here) and replaced, and other necessary repairs completed.

It is critical to understand how global NFB amplifiers work, because what you think you see may be the opposite of what’s really happening.

A scope, signal generator and good DMM are essential tools, as is a current limited variable AC supply.
Click to expand...
Yeah, I was fishing for some input on this problem specifically. Admittedly I'm no expert, but I studied the schematic and did some testing before asking any questions. That's how I arrived at a problem with the amp transistors. I think it makes sense that those being shorted out internally would overload the circuit output and cause that 5w resistor to fail and arc. If I'm correct up to that point I think it's impossible to ID the cause of the transistor failures, but I suspect it could be user error or just a faulty component. I'll read up on global negative feedback amps. What's nice with this bi amp set up is there are 2 identical power amp sections so comparing behavior is easy.
 
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#9
There’s nothing more specific to tell you.

You have identified bad part(s). Understanding how the amp works will show you which other component are vulnerable to collateral damage.

In that topology, it’s common for lots of collateral damage to occur.

Most of the Sanken power transistors from on-line sources are counterfeit, buyer beware.
 
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#10
Without a thorough working knowledge of that amp and its circuits, all you can really hope is that you get lucky. That being said, it is already toasty, so as long as you work safely, there is no harm in trying. Just know that now that you've messed with it, most qualified techs probably won't touch it.
 
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#14
General musings - There is also the bigger picture of electronic devices having finite life spans. No company builds an amp head expecting it to last indefinitely. Some companies build amps to higher standards and as long as they're not abused, they will last longer owing to better designs, components and assembly. Those companies also typically have better tech support and are likely to be able to fix a faulty amp.

Other companies build down to a low price point and those heads are going to fail sooner on. They also don't offer much service support. The idea is that the consumer throws it out at failure and buys another, like many things in our consumer economy. Then, of course, companies go out of business completely, or are bought out by conglomerates who cut the expenses of competent in-house support.

If a component problem arises with an amp head, then if it was reasonably recently built, there is a good likelihood that an expert trade person can source the required components and restore it to good working order. The older the head, the less the likelihood of sourcing exact replacement parts or functional equivalents. The topology of the amp head circuitry also plays a part in repairability -

There comes a time for every amp head that it either can no longer be repaired, or the cost to repair it will be too high. They really can't be recycled, so I ponder how many old discarded bass heads are in landfills across the world. Kind of depressing to think about, but it's reality.
 
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#15
Long story short: in a younger age I fixed and built (both from kit and from scratch) a bit g bunch of amplifiers.

Prior to that, I shotgunned parts and components like a drunk drummer goes through sticks. Undoubtedly replaced parts the didn't need replacement, wrecked good parts, spent way too much time and money.

I don't blame anyone for wanting to learn, or venture into unknown territory, yet I urge caution for life and limb as well as money.

Sometimes it is best to hoppity hop to a QUALIFIED repair shop.
 
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#18
DrEvil said:
Our bass player has a WT800C amp that he said he thought was running hot. We pulled the cover off to observe as he played it. A few minutes in, there was some pretty spectacular arcing between R27A and the speakon output (on the low out power amp side). Before this lighting show I noticed there was no heat being produced on that side. It seems that the power transistors were not operational beforehand. Checking them afterwards shows shorts between all legs. There are also several spots of heat damage on the board resulting in broken traces. Not sure if all of that is a result of the arcing. What I'm thinking of doing is replacing all burnt components and anything connected to any of the burnt up spots on the board, and bridging the traces with wire.

What I'm wondering is:
can anyone say what might have caused this? Maybe the amp has been run in bi amp and bridged mode at the same time in the past and some components finally failed. Or running bi amp with no load on that side? Or is it possibly an inherent problem with the amp?
Is it possible to get a new circuit board? Eden only deals with authorized service centers for parts like this. Meaning they won't help consumers working on Eden amps. How about recommendations for someone who can make a copy of the board?

Is there any issue using different types of solder together? I've been using Kester 63/37 rosin core. In removing a couple resistors from this board I found that my normal temp setting will barely melt the solder. Using different materials gets me thinking about galvanic reactions, corrosion, and overall bond compatibility.
Many thanks!
View attachment 4983969 View attachment 4983970
Click to expand...

Bummer. Good head. Hope you can get it sorted out.
 
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#19
I think step one is to throw the whole blessed mess into a dumpster and get a new head. (Or better yet take it to e-recycling as mentioned above.)

It sounds like a whole bunch of components could have been impacted and it could be tough to troubleshoot. And personally I'd never feel confident gigging it again.
 
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#20
smurfco said:
And personally I'd never feel confident gigging it again.
Click to expand...

This is where I end up at any time I have a piece of gear fail, which frankly has been a lot less than I probably deserve. You just don't know what is "working but damaged" and the days of me being able to go in with a multimeter and figure out the status of every component is about fifty years past. Modern amps just aren't built to do that.

I am not about to get up in front of a room full of people and have my amp:

1. do nothing, or worse
2. put on a pyro show for the crowd

It's gotta work as intended.
 
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