From: legg@nospam.magma.ca   
      
   On Fri, 22 Jul 2022 16:32:10 -0500, Peabody   
    wrote:   
      
   >ohg...@gmail.com says...   
   >   
   > > An easy test on this model is to unplug the harness   
   > > between the main board and the power supply and plug in   
   > > the AC.  With the main disconnected, the on/off line   
   > > pull-up resistor will put the power supply into   
   > > free-run, including the LED drive.  If the back light   
   > > comes on, the main *or* the power supply board is bad.   
   > > If the LEDs come on, post that and I'll walk you through   
   > > isolating the main or the power supply.   
   >   
   >Ok, so the main board controls the brightness of the LEDs   
   >through some kind of PWM signal to the power board.  If so,   
   >then it seems to me if the LEDs fire up when the main board   
   >is disconnected, then the main board is the problem -   
   >something is grounding that signal line.  It seems the power   
   >board has proved it's ok.   
   >   
   >But it does occur to me that if nothing else on the main   
   >board is bad, then you could replace the PWM signal with   
   >something coming out of an Arduino.  :-)   
   >   
   > > If the LEDs don't come on with the main disconnected and   
   > > the AC applied which is what I'm confident you'll find,   
   > > measure between BD9101 (either side) and J858 on the top   
   > > side of the board near the LED harness.  Should be more   
   > > than 150V-300V (depending on whether this uses 3V or 6V   
   > > LEDs) there between those jumpers.  If it's there or   
   > > higher, the problem is inside the display - either a bad   
   > > LED or open interconnect between the LED strips.   
   >   
   > > No voltage or low voltage between those points?  Bad   
   > > power supply.   
   >   
   >Yes, that makes sense.  I don't have a lab power supply, but   
   >if I could borrow one, it seems another test would be to   
   >disconnect the LED strips and reconnect them to a power   
   >supply.  You could ramp up the voltage to see if the LEDs   
   >light up at some point.  If they do, then they aren't the   
   >problem.  If they don't, something is open.   
      
   Just use a voltmeter. DC's good enough for this lamp   
   issue.   
      
   RL   
      
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