Re: Harman Kardon MAS101 Help me understand how this 5.6V_STB is created?
Thanks for your latest reply R_J. I had to put this on hold in favor of some TV and Xbox repairs.
Interesting developments! IC10 (FAN7602N) exploded... Flash of light, and nothing but a pile of ash. Or at least a big chunk of it is gone.
I simply replaced C18 (in the correct orientation) and I don't think I made a mistake, other than maybe if the flux I left on the board could create a short at the high voltages (~325 V) around that chip(?) I don't know. No charring on the bottom of the board though, so I'm skeptical.
What I found irregular even before this happened is how IC10's data sheet seems to suggest that the absolute max ratings for the LUVP pin is 10 V, but when I try to calculate that pin's voltage from the values in the schematics I end up with over 10 V on that pin:
I saw this as two voltage dividers:
Vdc = 380 V
R1 = 2 + 2 M
R2 = (1 M + 180 k) || (3 M + 27 k) = 850 k
Vi (intermediate) = Vdc * R2 / (R1 + R2) = 380*850/4850 = 66.598 V
R3 = 1 M
R4 = 180 k
V-LUVP = Vi * R4 / (R3 + R4) = 66.598*180/1180 = 10.16 V
Did I make a mistake? Otherwise, what does that mean? It's not supposed to operate even close to these limits, right? Not to mention beyond them.
Earlier, when I measured, that pin was indeed at 10.55 V. I have more like 392 V than 380 V on the bulk cap though, which nicely explains the 3% deviation.
* I noticed now that R98 is open and also seems to have blown, or at least absorbed some of the impact, since it has lost its outer coating opposite to the scorch mark from the exploding IC.
* And apparently Q14 has exploded. Shorted drain to source.
* R28 failed open.
* Short across D9/R19. Either or both shorted.
Now to figure out the chain of events. Any suggestions?
I'll be removing these components and measure again. This seems like a good opportunity to learn some new tricks.
Thanks for your latest reply R_J. I had to put this on hold in favor of some TV and Xbox repairs.
Interesting developments! IC10 (FAN7602N) exploded... Flash of light, and nothing but a pile of ash. Or at least a big chunk of it is gone.
I simply replaced C18 (in the correct orientation) and I don't think I made a mistake, other than maybe if the flux I left on the board could create a short at the high voltages (~325 V) around that chip(?) I don't know. No charring on the bottom of the board though, so I'm skeptical.
What I found irregular even before this happened is how IC10's data sheet seems to suggest that the absolute max ratings for the LUVP pin is 10 V, but when I try to calculate that pin's voltage from the values in the schematics I end up with over 10 V on that pin:
I saw this as two voltage dividers:
Vdc = 380 V
R1 = 2 + 2 M
R2 = (1 M + 180 k) || (3 M + 27 k) = 850 k
Vi (intermediate) = Vdc * R2 / (R1 + R2) = 380*850/4850 = 66.598 V
R3 = 1 M
R4 = 180 k
V-LUVP = Vi * R4 / (R3 + R4) = 66.598*180/1180 = 10.16 V
Did I make a mistake? Otherwise, what does that mean? It's not supposed to operate even close to these limits, right? Not to mention beyond them.
Earlier, when I measured, that pin was indeed at 10.55 V. I have more like 392 V than 380 V on the bulk cap though, which nicely explains the 3% deviation.
* I noticed now that R98 is open and also seems to have blown, or at least absorbed some of the impact, since it has lost its outer coating opposite to the scorch mark from the exploding IC.
* And apparently Q14 has exploded. Shorted drain to source.
* R28 failed open.
* Short across D9/R19. Either or both shorted.
Now to figure out the chain of events. Any suggestions?
I'll be removing these components and measure again. This seems like a good opportunity to learn some new tricks.
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