JoeMuc2009 wrote: > It is likely that the display filament power supply circuitry in your > Boom has failed. Many units suffer from this after some years. The > display itself is also wearing out, but if it goes all dark or starts to > fade from the outside edges towards the center, and sometimes recovers > after a few minutes of being powered-off, it's the filament supply with > 95% chance. > A VFD is basically an electron tube, albeit a pretty complex one. In > operation, it needs the filament (the six thin wires close to the front > side of the display) to emit electrons, so it needs to be heated. This > happens at a low voltage and a rather high power. The filament is fed +5 > Volts on the left side and between 2 and 3 Volts on the right, creating > a voltage drop between 2 and 3 volts. The higher this voltage drop is, > the more electrons are emitted (and the brighter the filament wires are > glowing). Besides the filament glowing brighter, the display's pixels > will also become brighter. > In 9 out of 10 cases, the failure is in supply for the the right side of > the filament. Instead of keeping a voltage around 2.5V, it ramps up to > 5.5V so it's even higher than the left side. This stops electron > emission gradually or completely. VFD experts at Noritake (the > manufacturer of the displays used in the Squeezebox range) call this > "filament starvation". > A Boom in operation has some hidden SMD parts behind the display that > get red-hot. I am pretty sure that the failure point can be found > somewhere in that area, however, it is practically impossible to find > suitable replacement components because the SMD markings don't tell > exactly enough what each component is for. > While I could not find a way to repair the root cause yet, I found a > workaround that turned out to work fine for many people who sent me > their Boom for a display replacement. The fix is this: > > 22025 > > I am using three run-of-the-mill diodes, each of which has a known > voltage drop of around 0.7V. Three of them in series make a total > voltage drop of about 2.1V. I am using them to pull down the voltage on > the filament's right side. Diodes are needed because current must not > flow from GND towards the filament pins. GND can be found in each of the > screwholes so that is an ideal point to solder (as long as you leave > enough room for the screw). > The diodes can be packed together closely, shrink-wrapped, and hidden on > the backside of the board. > This little trick ensures that voltages on the right will never exceed > ~3V as 2.1V are always subtracted by the diodes. So even if the > gone-crazy Boom circuitry is sending +5.5V in, we will make 3.4 out of > it which is in the acceptable boundaries. 2.9 Volts are still fine, > actually we should just stay below ~4 Volts on the right to ensure a > voltage drop big enough for the whole thing to work. > The fix works for all brightness levels also. I found that an intact > Boom is regulating the right side of the filament with different > voltages, depending on the selected brightness. It does not make much > difference though if we use diodes to make kind of a fixed voltage out > of it. > So you might give this a try, because this will help you a lot more than > a new display that would also stay dark if the power supply circuit is > broken :D > > Oh, by the way, the image may suggest that you need to connect the > diodes to the middle pin of the 3-pin block at the right side of the > display. Not quite, all these three pins are connected, inside the > display as well as on the PCB, so you can best solder the first diode > across all three pins to ensure a perfect connection. > > Cheers, > Joe
Why not putting just a single Zener of say 2.5V to produce the voltage gap? LMS 7.7, 7.8 and 7.9 - 5xRadio, 3xBoom, 4xDuet, 1xTouch, 1 SB2. Sonos PLAY:3, PLAY:5, Marantz NR1603, JBL OnBeat, XBoxOne, XBMC, Foobar2000, ShairPortW, JRiver 21, 2xChromecast Audio, Chromecast v1 and v2, , Pi B3, B2, Pi B+, 2xPi A+, Odroid-C1, Odroid-C2, Cubie2, Yamaha WX-010, AppleTV 4, Airport Express, GGMM E5 ------------------------------------------------------------------------ philippe_44's Profile: http://forums.slimdevices.com/member.php?userid=17261 View this thread: http://forums.slimdevices.com/showthread.php?t=106381 _______________________________________________ Boom mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/boom
