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johnboy183
Senior Member
Last Activity: 07-20-2023, 10:47 AM
Joined: 05-11-2008
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    A further finding if you read the above. Testing voltages while the leds flash or remain constant for a few seconds shows on Q511 (FQD6N25 6N25 TO-252):
    LEDs dim G = 11.9v
    D = 7.0v
    S = 7.0v

    LEDs lit G = 11.9v
    D = anywhere from 56.0v to 0v
    S = 0-1v
    Also when power is switched on or off and running up to standby the Gate on this fet = rapidly changing voltages between 4 and 60v
    Maybe this is normal - do you reckon?
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    Hi Budm
    Finally back home and yesterday fitted the replacement Q502 and U500.
    Fired the PSU up with LEDs connected and measured the voltages on U500:
    Pin 1 COMP 2.55v
    Pin 2 EN 3.2v
    Pin 3 DBRT 0.16v
    Pin 4 GND 0.0v
    Pin 5 OSC 0.0v
    Pin 6 ISET 1.5v
    Pin 7 BOSC 6.5v
    Pin 8 LED4 7.0v
    Pin 9 LED3 7.0v
    Pin 10 LED2 7.0v
    Pin 11 LED1 7.0v
    Pin 12 OVP 0.6v
    Pin 13 ISENSE 0.0v
    Pin 14 GATE 0.0v
    Pin 15 VIN 11.8v
    Pin 16 VCC 5.9v

    LED+...
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    Sorry BudM got to be away on business for a couple of weeks so post will be silent until my return.
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    Ok thanks.
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    Yes - FQD7N30 is Q502
    Do I take it from what you are saying that the shorted Q502 has therefore damaged the latest U500 and the only solution is yet another new U500?
    If I replace Q502 and U500 do you think its reasonable to expect the board may now function without damaging the U500?
    Thanks again
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    Just a follow up on above. As the accidental short happened BEFORE this latest U500 was fitted there has to be an external reason it has now faulted. Do you think the shorted mosfet could have been the culprit as I have yet to find any other failed component so far?
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    An update on earlier:
    In 6) I incorrectly typed Pin 2 instead of Pin 15 so ignore that typo.
    Have powered up the board with FQD7N30 left out of circuit and now its Drain and the LED connector + pin again read 156v
    Have disconnected the trace from S505 along its path to Pin 15 at various points ( via jumper pins and joints) testing up to each disconnection and right up to Pin 15 ( if Pin 15 is disconnected from its pad) it retains 11.9 volts at every point along the way until Pin 15 and its pad are reconnected when...
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    I need to fully understand what you are saying here, and I don't unfortunately.
    1)Are you agreeing that Q502 is dead and requires replacement?
    2) Are you saying that the second fitted new U500 is now damaged and that is because up to 12 volts has been coming through it via the mosfet drain? (since the new U500 was fitted there has been no voltage larger than 11.8 volts recorded on the mosfet GD or S or any other component in this part of the board)
    3) Or are you meaning that U500 is damaged as a result of the 42.3mA...
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    S522 is there and close to it is S526. S529 is also there.
    Yes - one end of S505 goes directly to Pin 15 Vin. The other end connects directly to S522/S529 /Q214 solder pad.
    Working on the board today I began to suspect Mosfet Q502 (FQD7N30) and have removed from the circuit. It tests faulty.
    On diode setting with red on Source + black on Drain = 0.158. Reverse the leads reading = 0.157. Gate to Drain with red on drain= 0.326 and the same reading if probes reversed. Gate to Source red and black in both directions...
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    You say above "the problem is around that IC and associated parts around that IC." Which "IC" do you mean in this comment so I can concentrate on that?
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    Finally found location of Q214 position and as you can see it is absent...
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    Here is a photo of S505 on the board unless I am misreading the board marking...
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    1) Well aware Q511 as a mosfet is a switch - why does it have have 11.9v on all three pins?
    2) As I indicated above that I measured both sides of S505 (it is a resistor marked 101) I'm not sure why you are asking if its present? If its simply a jumper why can it have 11.9 volts on one pole and 7.67v on the other? I need to understand its function.
    3) Yes i know which would be pin 1
    4) As said above S505 is on board. Have just been out to the workshop to look at board and cant find any 8 pin IC marked on board as Q214....
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    "Power on Vin = 10.8 volts
    Power on Vcc = 5.0 volts"
    I cant answer this other than I wonder if the low MDM battery was starting to kick in then skewing the readings.
    Will try what you suggest tomorrow.
    Is having 11.9v or 7.6v on all 3 pins of Q511 normal behaviour?
    Also have you any comment on why S505 can have 11.9v on one pole and 7.6v on the other pole if its simply a resistor - or is its purpose to act as a safety?
    Also the Q214 datasheet I can find does not clearly identify the Source,...
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    Just another glitch with this whole project -- battery was dying in MDM I now find ( presumably as it had been on for a long time during the day of testing plus the battery in it was a rechargeable which I dont normally use as they seem to sudden death but only one I had ).
    Checked as many of the measurements I gave you yesterday as I could and they all were the same except for the main discrepant voltage readings:
    Voltages measured at Main board connector:
    12 volt shows 11.9 volt consistently now
    24 volt shows...
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    Well as promised spent an extensive day of checking and testing using your suggestions.
    First with all components in and no power on I checked the following readings:
    on 200 ohm scale:
    Pin 13 to ground = 11.4 ohms
    R522 to ground = 11.4 ohms
    C519 + to ground = 11.4 ohms
    C 519 - to ground = 0.2 ohms
    R522 out to ground = 0.4 ohms.
    R522 disconnected from Pin 13 trace then Pin 13 to ground reads 1
    C519 removed and tested on 2M scale reads 6.6 continually rising.
    With R522 and C519...
    See more | Go to post

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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    I had already said in post # 73 that the new IC was in place. So the figures I gave above were with the new IC . Given the poor pad and traces serving the IC I had checked for solder bridging and bad joints at the time I installed the IC and all appeared fine. The only possible bridge was where a trace goes directly under C519 so the bulky solder joint made to connect Pin13 trace, R522 missing pad and the trace to C519 could have bridged that but again before the measurements above were taken the joint was cleaned, reduced and can...
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    Further update.
    You commented "also pay attention as to what the value of R522 is installed on your board". I had mentioned that in my post #67 the schematic said it was 330K but mine was marked 100 or only 10 ohms. So the Resister I put in was 11ohms ( nearest I had)(could that be the reading of 0.11 obtained earlier)
    In terms of the grounding you were spot on. The board is not attached to the chassis and I was using ground on the hot side. When tested with the right ground point Pin 13 shows 000
    If I disconnected...
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    Hi
    I think some of our messages or thought processes are overlapping hence the confusion. Also I am using some abbreviations of my own making I think.
    I always understood (probably wrongly) that smd caps could only be tested properly out of circuit hence my comment of not sure of best way to test C519 in situ. All I could do was to put the black lead to one end of cap and the red to the other which showed 0.11 ohms with no increase of reading if probes left on.
    The rest of that sentence I was wrongly describing what...
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  • johnboy183
    replied to 17IPS20 No Led Voltage Solved With Video :)
    in Troubleshooting TVs and Video Sources
    Re: 17IPS20 No Led Voltage Solved With Video

    Have now reinstalled the last new MP3394 (very difficult as pads and traces now very poor!).
    When I test Pin 13 to the board earth I get Infinity but if I put the black probe on Pin 4 (grnd) I get OC !! Why is that?
    If I fire up the board with the shorted cap still in place to test Vcc am I liable to damage the IC ?
    See more | Go to post

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