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TC Electronic BH550 went bang!


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Basically what the title says…

Practicing today at home, the amp went bang as I switched the power off. The mains tripped and there was the expected electrical burning smell.


Popped off the cover, and the internal fuse is gone as expected. But also this component labelled VRD100. A piece of it has come right off.


I’m not adverse to replacing it, doesn’t seem a particularly difficult soldering job. Assuming I can source the part of course!


Slightly concerned about the surrounding parts too, particularly the white rectangular part next to it.


Just putting it out to the experts before I dive in!




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VDR = voltage dependent resistor. Used for slow start of the electrical units. It cuts the current peak when the cold unit is started.

The white part could be a resistor or rather, a capacitor. You need to check the numbers and codes.


Because the unit has failed, it is reasonable to study the surroundings very well and thoroughly. Power failure may be just a part or two, but a DC connected system may die down to the power and preamp. Please consult some tce accredited repair company. Just in case.

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A fairly positive update...

It turns out my singer's neighbour is a retired electrical and electronics engineer, who still occassionally fixes PA gear and amps for local bands.


He's been quite frustrated that he can't lay his hands on a service manual for this or anything similar, but has having a go anyway. He's replaced an internal fuse and tested several components in the vicinity of the blown VDR - and they are apparently fine. He's actually temporarily got the amp running without the blown VDR - though it's apparently needed for safety, so he's going to source a replacement for it.


Hopefully he gets this back up and running. Though I think I may still buy an extra small amp as a backup given how cheap some of these micro class D amps are!

Edited by geoham
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On 07/08/2021 at 17:03, MoonBassAlpha said:

It's entirely possible that it's just the vdr itself that has failed,  for no particular reason. 

I’ve spent some time reading about VDRs, and this seems entirely plausible. It doesn’t seem particularly rare, and I wonder how many otherwise working devices are scrapped as a result. 


The guy trying fix my amp seems to think this is likely the case too, and the amp is currently working with the VDR simply removed from the circuit. He’s waiting on a replacement being delivered from China - hopefully it should be returned to me in the next few days.



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  • 2 weeks later...

Hopefully the end of this tale... Got the amp back on Saturday. VDR and internal fuse replaced. Working fine at home volumes. I'm very pleased. A by product of this is that I now have a backup amp, in the form of the Trace Elliot Elf. Or perhaps this one is the backup. Time will tell! I'll perhaps take it to this Saturday's gig with me to put it through its paces.



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