Sometimes you just get that lemon. Always breaking, always something new. And during increasingly-impatient repairs, shortcuts otherwise not taken just make it worse. Herewith a saga of my Battle of the Active Tannoy.
They say a mechanic's car is always broken. I can certainly profess to that. My main hifi system is almost always 'temporarily' out of action while something is being changed. But then there are the things that you buy purely to do their job, and when they fail one starts muttering.
The Tannoy Precision 8D is a single 8" active speaker I bought as a reference lab speaker to test designs with via a little Behringer mixer, very useful. Since it was an orphaned single speaker, I got it at a reasonable price. But even from the get-go, there were strange scratchy sounds in the background. Now, I cannot debug the stuff I test if the reference monitor adds artifacts of its own. So, open it up. Except this thing was built to withstand an earthquake: it will comfortably pass the avionic shock & vibration test requirements. All connectors are firmly glued in, all the screws threadlocked and the PCB components are coated with this yucky caramel-type substance. Great for mechanical integrity but the sods at Tannoy either didn't know or care that it's corrosive in the long term, so the boards are fragile. Components cannot get measured because of the muck, traces peel loose, fresh solder can't reach through it. In addition, the regulators got so hot that the entire section around them were scorched.
But, I persisted. Removed all the glue, cleaned all the parts as far as possible and recapped everything that could possibly contribute. Mounted power resistors on the plate to drop the input voltage of the regulators, now they run much cooler. Strangely enough the crackles still initially persisted somewhat and then went away. Score. I also found that one of the control switches on the back didn't work. Fortunately a dab of solder on said corroded joint fixed it.
For a year or so, all is bliss. Then one day.. the surround of the coax has a large tear. Pushed it in a bit and the tear doubled in size. So it means a trip up to the Northern Subs to get Riaan to replace it, which got deftly postponed until last week. In the meantime, it still did its job surprisingly well with just some honkiness in the bass. When removing the driver it was stuck in so tight it broke the tips off two screwdrivers.
Then suddenly.. silence. Opened it up, lots of debugging through the muck. Finally found that a temperature sensor's faulty trace kept the amps in mute. Hard-wired it, great it works.. for one day. Thought it was just a quick job, so fitted it in yesterday morning. Turned out more complex, ended up simulating the whole protection circuit to make sure my mind is not going whack. Shorted out the wrong resistor, poof goes a transistor. Fortunately I had a compatible replacement at hand. Finally traced it to a 4.7uF 100V capacitor that seemed to have gone open-circuit. No biggie, except I don't have anything to replace it with. Since I knew the application, a larger one would work, so two series 220uF 63V caps tack-soldered in gave a 110uF result. Cool! It works fine. But the two caps are cumbersome. Dug further in my junkbox and found a single 220uF 100V that'd be much easier to mount. Put it in, already began getting ready for spending the remainder of Women's Day watching TV.. poof, pop, smoke. Turns out the cap's charge current was too high that caused a trace to disintegrate and a diode to pop. OK, hard-wire the trace. Search for 20minutes for an appropriate diode and smaller cap. Found something for both. 24h later and despite numerous power-cycles and hot and cold restarts etc. and all still seems to be working well. Just need to go get the driver from Riaan and all will be well. Oh wait, what's that? Ah, the TRS audio input plug seems to be loose. Someone in the past must have yanked on the cable. You need to fiddle with the plug or the audio distorts..
No pictures in this one I'm afraid, the end result is something I'd sternly speak to one of my engineers had they done it..
As summary:
Purchase cost: R2000
Materials & driver repair: R1800
Time: 40h (conservatively) in numerous sessions
They say a mechanic's car is always broken. I can certainly profess to that. My main hifi system is almost always 'temporarily' out of action while something is being changed. But then there are the things that you buy purely to do their job, and when they fail one starts muttering.
The Tannoy Precision 8D is a single 8" active speaker I bought as a reference lab speaker to test designs with via a little Behringer mixer, very useful. Since it was an orphaned single speaker, I got it at a reasonable price. But even from the get-go, there were strange scratchy sounds in the background. Now, I cannot debug the stuff I test if the reference monitor adds artifacts of its own. So, open it up. Except this thing was built to withstand an earthquake: it will comfortably pass the avionic shock & vibration test requirements. All connectors are firmly glued in, all the screws threadlocked and the PCB components are coated with this yucky caramel-type substance. Great for mechanical integrity but the sods at Tannoy either didn't know or care that it's corrosive in the long term, so the boards are fragile. Components cannot get measured because of the muck, traces peel loose, fresh solder can't reach through it. In addition, the regulators got so hot that the entire section around them were scorched.
But, I persisted. Removed all the glue, cleaned all the parts as far as possible and recapped everything that could possibly contribute. Mounted power resistors on the plate to drop the input voltage of the regulators, now they run much cooler. Strangely enough the crackles still initially persisted somewhat and then went away. Score. I also found that one of the control switches on the back didn't work. Fortunately a dab of solder on said corroded joint fixed it.
For a year or so, all is bliss. Then one day.. the surround of the coax has a large tear. Pushed it in a bit and the tear doubled in size. So it means a trip up to the Northern Subs to get Riaan to replace it, which got deftly postponed until last week. In the meantime, it still did its job surprisingly well with just some honkiness in the bass. When removing the driver it was stuck in so tight it broke the tips off two screwdrivers.
Then suddenly.. silence. Opened it up, lots of debugging through the muck. Finally found that a temperature sensor's faulty trace kept the amps in mute. Hard-wired it, great it works.. for one day. Thought it was just a quick job, so fitted it in yesterday morning. Turned out more complex, ended up simulating the whole protection circuit to make sure my mind is not going whack. Shorted out the wrong resistor, poof goes a transistor. Fortunately I had a compatible replacement at hand. Finally traced it to a 4.7uF 100V capacitor that seemed to have gone open-circuit. No biggie, except I don't have anything to replace it with. Since I knew the application, a larger one would work, so two series 220uF 63V caps tack-soldered in gave a 110uF result. Cool! It works fine. But the two caps are cumbersome. Dug further in my junkbox and found a single 220uF 100V that'd be much easier to mount. Put it in, already began getting ready for spending the remainder of Women's Day watching TV.. poof, pop, smoke. Turns out the cap's charge current was too high that caused a trace to disintegrate and a diode to pop. OK, hard-wire the trace. Search for 20minutes for an appropriate diode and smaller cap. Found something for both. 24h later and despite numerous power-cycles and hot and cold restarts etc. and all still seems to be working well. Just need to go get the driver from Riaan and all will be well. Oh wait, what's that? Ah, the TRS audio input plug seems to be loose. Someone in the past must have yanked on the cable. You need to fiddle with the plug or the audio distorts..
No pictures in this one I'm afraid, the end result is something I'd sternly speak to one of my engineers had they done it..
As summary:
Purchase cost: R2000
Materials & driver repair: R1800
Time: 40h (conservatively) in numerous sessions
