when i turn on, Philliips TV is not on
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Re: when i turn on, Philliips TV is not on
Just check C955/954 in circuit.Comment
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Re: when i turn on, Philliips TV is not on
You needed to replace PC901 NOT pc902 I only suggested exchanging them if you did not HAVE ONE.Comment
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Re: when i turn on, Philliips TV is not on
I suspect that the two points only get connected whn the main board is connected, something only Philips would do.
The grounds I marked in Blue, DO NOT connect to the grounds I marked in Green, this is why the supply has no reference and why the output is too high. Installing the J14 jumper should result in a stable +5 volts.Last edited by R_J; 01-30-2020, 02:37 PM.Comment
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Re: when i turn on, Philliips TV is not on
Had you told me the voltages on IC951 earlier, I would not have suggested the capacitorsT he caps will be ok, Install the jumper wire I suggest this will fix this issue.Last edited by R_J; 01-30-2020, 02:40 PM.Comment
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Re: when i turn on, Philliips TV is not on
The cap is likely .1ยตfLast edited by R_J; 01-30-2020, 03:16 PM.Comment
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Re: when i turn on, Philliips TV is not on
I am outside now, I will do the jumper and update later. ThanksComment
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Re: when i turn on, Philliips TV is not on
Install a TEMPORARY jumper wire in J14, as the power supply board does NOT connect the negative side of C951A/B to the negative of IC951. WITHOUT this connection, the power supply standby 5 volts has no reference.
I suspect that the two points only get connected whn the main board is connected, something only Philips would do.
The grounds I marked in Blue, DO NOT connect to the grounds I marked in Green, this is why the supply has no reference and why the output is too high. Installing the J14 jumper should result in a stable +5 volts.
I checked around IC951
R955 = 1.4v
C955 = 1.4v (which is connected to ref of IC901)
C954 = 1.4v (which is connected to ref of IC901)
ZD907 = -5vComment
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Re: when i turn on, Philliips TV is not on
Yes I put back the original oneComment
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Re: when i turn on, Philliips TV is not on
Did you ever replace C951? The feedback circuit is very simple I don't know what could be causing it not to work, Have you checked that all the resistors have the correct resistance, even R952.
R954 and R955 set the voltage for the reference pin on ic951. If the voltage on C951A is too high (or has too much ripple) IC951 should start to conduct and lower the voltage on PC901 pin2, this lights the led in PC901 telling ic901 to lower the voltage, this is how it regulates.
As you can see, if the feedback is not working, IC901 operates full, and the result is too high a voltage on ZD951/C951A. If it was'nt for ZD951 (6.2v zener) clamping that voltage it could be 10 volts or more.
The problem is in that feedback circuit.Comment
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Re: when i turn on, Philliips TV is not on
Did you ever replace C951? The feedback circuit is very simple I don't know what could be causing it not to work, Have you checked that all the resistors have the correct resistance, even R952.
R954 and R955 set the voltage for the reference pin on ic951. If the voltage on C951A is too high (or has too much ripple) IC951 should start to conduct and lower the voltage on PC901 pin2, this lights the led in PC901 telling ic901 to lower the voltage, this is how it regulates.
As you can see, if the feedback is not working, IC901 operates full, and the result is too high a voltage on ZD951/C951A. If it was'nt for ZD951 (6.2v zener) clamping that voltage it could be 10 volts or more.
The problem is in that feedback circuit.
No I didn't replace C951.
R952 = 1.991k
R954 = 6.01k
R955 = 2.951k
"*set the voltage for the reference pin on ic951." Am I using external power supply at what voltage, while the board plug in the outlet? I am confusedComment
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Re: when i turn on, Philliips TV is not on
What I said was that R954 and R955 set the voltage for the reference pin on ic951, thats how the those reference ic's work. R954 and R955 form a voltage divider, So when the voltage on the top of R954 increases, the voltage on the other end of R954 increases, this will cause IC951 to turn a bit more lowering the voltage on PC901 pin 2.
But this is not happening so the led in PC901 never turns on.Comment
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