chill wrote: > Hi Joe > > I've read your blog posts on the main VFD replacement and the diode fix, > and must say that they are very nicely written - clear, detailed, and > well illustrated. I have quite a collection of Booms and I expect to > take on one or other of these jobs in the near future. > > As a point of interest though, can you explain a detail that I don't > quite understand? You have explained that the variable voltage on the > right side is intended as a way to control the display brightness, but > you also say that it remains possible to vary the brightness even after > your diode fix, which I understand creates a fixed voltage drop. Do you > know how the brightness remains variable even with this constant voltage > drop?
Thanks for the praise! I'm happy it helped you. Actually I can't explain what good that circuitry is as the brightness control is just as good with the fix (and permanent voltage on the F2 lines) as it was without. The Noritake MN16032 display offers four brightness levels for each pixel so actually this would be sufficient already. And Logitech actually makes use of this which can be observed if you have a visual effect such as the VU meters or spectrum analyzer active. They will use some shading / brighter peak indicators in high brightness levels whereas everything is the same brightness in lower settings. The Squeezebox firmware offers "off" and five brightness settings so they use the built-in display capabilities as well as controlling the filament voltage. The latter won't work of course after the fix was applied. I think the mode in which this should be most apparent is the low brightness levels as this is when the grid voltage differential is rather low. I have taken measurements in all brightness settings, and this confirms the theory that a higher voltage differential (i.e. less voltage on F2 while F1 is constantly at +5V) causes higher brightness: Level 5: 1.418 Volts Level 4: 1.414 Volts Level 3: 1.413 Volts Level 2: 2.513 Volts Level 1: 2.511 Volts You see that the F2 voltage at lower brightness levels goes up. If the internal power supply circuitry is at fault, F2 goes up as high as +5V also. The 3-diode fix will pull the F2 voltage down by approximately 2.1V to ~2.9V. This is still not as much of a voltage differential as in the original but I did not observe any visual difference. Using fewer diodes will cause the remaining diodes to become considerably warm which will probably destroy them over time. Using more diodes will cause a higher voltage drop, thus the filament to glow which is visually disturbing and will also cause the filament to suffer. Maybe it is a combination of the diodes and what remains from the defective circuitry that keeps this working. Anyway, so far every fix worked and nobody ever complained. We will never fully understand this as long as Logitech keeps it all secret. PN me if your Boom / Classic / Transporter display has issues! Blog: https://www.blogger.com/blogger.g?rinli=1&pli=1&blogID=5053304027701850753#allposts ------------------------------------------------------------------------ JoeMuc2009's Profile: http://forums.slimdevices.com/member.php?userid=23131 View this thread: http://forums.slimdevices.com/showthread.php?t=107535 _______________________________________________ discuss mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/discuss
