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The Tannoy VNet 218DR is a fuknuge box weighing approximately a billion tons. It contains two 18 inch speakers and an amplifier.
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The front panel of the amp. This is all that is visible to the outside when it is assembled into the cabinet.
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The amp is not made by Tannoy but is something called an XPOD-HP made by Linea Research. |
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Top view of the assembly. The SMPS and the amp are constructed on a single large PCB which is fitted into a U-shaped aluminium heatsink. All the power devices are bolted to this, which means to get under the PCB I have to remove nearly three million nuts and bolts and stuff. |
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A bowl containing the many millions of things which must be unscrewed to get the PCB out. If you count them after a few drinks, there are even more. |
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Internal construction, glass fibre reinforced silicone rubber sheet for metal devices and grease on the other things. |
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The bridge and a couple of regs mounted on pink insulator. |
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The DSP circuits at the front end are on plug-in subassemblies. |
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See how one of the subassemblies is made of two boards back to back. I don't see that every day. |
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The underside looks OK, no burnt stuff. |
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The bridge was suspected but checked out OK. Added to my suspicions that this is a British-designed item but assembled in China. |
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The shorts seem to be at these IGBTs, CE is short, there is gate to CE conduction and Collector to chassis short, but no apparent damage to the driving tackle. So with a bit of luck, these are all that will need to be replaced. |
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The ruptured insulation on the back of the IGBTs. Poor work during assembly coupled with poor choice of materials and careless design. The rectified mains volts are on the back of these transistors and it's not totally impossible for someone to become dead as a result. |
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The shorts to chassis have damaged the aluminium. |
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A couple of pics showing the state of the pink insulator. It's nice and soft but very easily damaged by careless work. |
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The damaged parts out, 40N60 is a chunky device. |
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Here are the replacement transistors, ON Semiconductor NGTB40N60FL2WG. Notice how the epoxy extends completely around the back metal and so a sharp metal edge will not be pressed into the insulator. |
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Cleaning the mounting face. Under the crap, it turns out to be well enough finished. |
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These grey insulators have more robust glassfibre included in them and I have dressed the leads so that the top edge of the transistors is not trying to cut the insulators. I am fairly confident this will be fine, though the electric field here is somewhere around 2.4MVm-1 a scary-looking number. |
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I have used the same material to replace the other pink stuff. |
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During reassembly. Some of those metal clips have very little clearance to the devices with exposed metal. I really don't think this is a good idea. |
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After reassembly. |
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