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  1. #41
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    Re: Help needed to repair a Sony Trinitron KV-2165MT power failure

    You may have an open-circuit R609, which will remove the ground reference from pin 2. This resistor senses peak current through the STR and could have gone open due to the fault.

    Below is an internal diagram of the STR chip to help understand the working. R609 (R805) can be seen to be in series of the main switching transistor.

    When the peak emitter current is too high, the voltage drop over R805 will turn on VT3's base-emitter junction, which will turn on VT2, that will shunt current away from the base of VT1, turning it off.

    The opto feedback performs the same function. When the 112/5 V line goes too high, opto turns on, turning on the external PNP (Q801), which also turns on VT2.



    •   Alt16th February 2018, 04:09

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  2. #42
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    Re: Help needed to repair a Sony Trinitron KV-2165MT power failure

    Unfortunately, R609 is still intact!

    By the way, what is the source for the 115V in this board? As far as I can see, it's T601. So, why the cathodes of D604/D608 read 81.7V ?



  3. #43
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    Re: Help needed to repair a Sony Trinitron KV-2165MT power failure

    Let's think about this:

    You measured the voltage on C604.
    The reading across C604 pins was around 320 VDC
    You said that you measured a low resistance between pin 1 of the STR and C604 positive.
    Resistance between Pin#1 of STR and C604 is 0.1Ω
    Then you said that you didn't measure any voltage between pin 1/2 of the STR.
    Pins 1/2 of STR: 0 VDC
    If we follow pin 2 back through R609, it goes to the negative rail which is connected to C604 as well.
    Unfortunately, R609 is still intact!
    Should be 0.15 Ω

    So, something is not making sense . How can you measure 320 VDC on C604, but get no voltage on pin 1 of the STR? You already stated that there is a very low resistance between pin 1 and C604. You may have a broken pcb track between R609 and DC GND which will cause these strange readings. Inspect the tracks for GND continuity to R609.
    You should carefully do the measurements again. Perhaps you referenced the meter probes between the wrong points when taking voltage measurements. I would suggest keeping the negative probe of your meter fixed on the GND side of C604 and remeasure on positive of C604 as well as pin 1 of STR.



  4. #44
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    Re: Help needed to repair a Sony Trinitron KV-2165MT power failure

    Yes, you were correct, it's a bit confusing. In fact, because of the dozens of tests I've done switching to different GND points, different AC/DC modes, I got almost lost in the dark.

    But what I'm pretty sure about is that I didn't read any voltage across Pins 1/2 of the STR.

    Yes, I believe it was around 0.15Ω.

    I won't be surprised if the board has a broken trace as I have already found a lot of dry and cracked solder joints across the entire board.

    I will do the tests as you suggested, and I will try to trace the GND back through the R609 and will let you know as soon as I can.

    Thank you for your help!

    - - - Updated - - -

    Now, I have an update regarding the older set, the KV-2162M9, which was working lately. I have replaced the 400V/220uF caps, as well as, the 160V/330uF. The clicking sound has gone now, but the set still refuses to start up. When turning power on, the set makes a loud noise just like if it's starting up normally, screen shows tiny flashes on certain corners for a bit of a second, then the power LED goes off. When turning off, it makes that crackling noise as well, which might be indicating the PSU is working well?



  5. #45
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    Re: Help needed to repair a Sony Trinitron KV-2165MT power failure

    Hello guys,

    I'm back with some interesting results so I really appreciate your further assistance.

    As e-design said, it didn't make sense that I got no voltage across Pins 1/2 of the STR while the reading was 320 VDC across C604 pins. Pins 1/2 of the STR are connected directly to those of C604, so it's really weird that I didn't get any voltage there. I decided that I should spend more time investigating that area and below are the results I have obtained.

    First of all, continuity test between STR Pins 1/2 and C604 checks, so probably I don't have a broken trace in between. Second, I have taken the following measurements with the negative probe of my DMM fixed on the negative pin of C604:

    1- STR Pin 2: 318 VDC
    2- Q603: All pins read 318 VDC
    3- Q601: Same as Q603, with the exception of making some fast oscillation/hissing noise out of some other component, probably a cap or the transformer or the STR itself, when touching the base with the probe.
    4- Pins 4/5 of IC603 read 318 VDC.

    When fixing the positive probe on the positive pin of C604 instead and taking measurements with the negative one, the results are totally different. Pin 1 of STR reads OL, no voltage whatsoever. Again, reading Pins 1/2 of the STR directly results of OL, too. The funny things is, I can read the voltage across the cap (C604) in different polarities (318 VDC or -318 VDC) but it's not the case on Pins 1/2 of the STR, where the reading is always OL. Pretty weird, isn't it??

    Now, the serious fun started when I switched to my analog multimeter. What follow are the results I've got:

    1- Negative probe of the analog meter is fixed on the negative rail of the bridge rectifier/C604. The meter is set on 1000 VDC, 250 VDC would be out of range as we are measuring a potential of more than 300 VDC. When measuring Pin 1 of STR, the meter reads 110 VDC (again, the scale is 1000 VDC). All other pins read 0 or OL, but pins 8 and 9 pull the needle back (negative reading).

    2- Q603 gives around -1.5 VDC on all of its pins.

    3- PS801 (the 115V line) turns out to be 60 VDC when measured with the analog meter (reference is cold GND).

    4- No output whatsoever on any pin of the secondary side of T601, except 1 VDC on Pin 12. (reference is still cold GND).

    5- Back to STR again, the reading I got with the analog meter was really strange, considering the earlier results. Pins 1/2 now read a voltage close to that of C604, but it was higher by almost 30 VDC. On a scale of 1000 VDC, the reading was 110 VDC across Pins 1/2 of STR, while it was around 85 VDC across C604, which is supposed to be the source for that voltage on the STR.

    Finally, when getting back to the DMM, using the cold GND, I got the following measurements, which are somewhat corresponding to those on the schematic:

    1- STR Pins 2 ~ 9: - 57 VDC
    2- IC603 >>> Pin1: 14.75 VDC, Pin2: 14 VDC.
    3- Q603: -58 VDC on all pins

    Thank you again for your help!



    •   AltToday, 01:59

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