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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.



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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.



    •   Alt17th February 2018, 01:21

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  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?



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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!



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    Re: Help needed to repair a Sony Trinitron KV-2165MT power failure

    1- STR Pin 2: 318 VDC
    Are you sure? Measured between negative C604 and pin 2?
    Can't see how this can be possible as pin 2 goes back to negative via R609 (0.15 Ω) and should be near 0 V
    If this was true, then R609 would have blown open long ago. That will happen if the internal switch in the STR goes short collector-emitter.

    Please keep your one probe on C604 neg and measure STR pins 1-9.

    When you measure the 115 V then your -probe should be on GND side C609



    •   AltYesterday, 03:12

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  7. #47
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    Re: Help needed to repair a Sony Trinitron KV-2165MT power failure

    Hello e-music,
    I deeply apologize for the long absence.
    My wife's PC decided to pack it in, and she had important work to complete, so she had to
    sponge my computer until she was done.
    I have to admit that I require some time to answer any posts, as I like to think of as many
    alternatives as possible before uttering a word.

    OK, first up, I need to know exactly what component/s have been replaced in this set. We'll
    get to the other telly later.

    When ever you do any static measurements, to be 100% on a component, you need to either
    lift one leg out of circuit or in the case of capacitors, remove them entirely. This is to ensure
    that no other components in circuit will affect any of your readings.
    SMD is the same, you need to remove the part entirely, as unfortunately you can't lift a leg.

    E-design is correct.

    How can you measure 320 VDC on C604, but get no voltage on pin 1 of the STR?
    It definitely makes no sense.
    Due to the PSU not oscillating you should be getting an identical voltage on Pin 1 of IC601, as its
    only passing through a virtual short circuit via the chopper transformer. But when it is oscillating,
    the 81.7 volts shown in the schematic would be correct, and not be at the same potential as C604.

    I need you to measure R615. But make sure you lift one leg out of circuit, then get your reading.
    This component should be the start-up resistor for IC601.

    If you have a look at the picture below, it will show you the drive needed for Q3 of the internal
    diagram:



    If you find that R615 is OK, then we need to check the 3 diodes in the PSU for leakage.
    Once again, lift one leg on each of the diodes (D602, D603 and D607).
    Set you multi-meter to diode test and measure them both ways. One way (Positive probe to anode
    and negative probe to cathode [Forward-Biasing]) you should get a reading. Something like .607
    or there-about's.
    You should get an open circuit reading the other way around [Reverse-biasing].

    If you find the readings correct, we need to do what they call, "a punch-through" test on them.
    Set your multi-meter to the highest ohms setting it has, then measure each diode reverse-biased.
    If you get any reading at all, then there's a good chance the diode/s are leaking.
    No point doing a forward-bias test, as the readings won't mean anything on high ohms.
    If you need to replace D603 and/or D607, you can replace either with an 1N4148. They are as common
    as muck.
    You can replace D602 with an FR504, BYT52G or BYV13. Not as common, but source-able.

    If all is well, we now need to start measuring resistors, that have either gone high in value or open
    circuit.
    Do an in-circuit static ohms measurement on each one first, and if you're getting obscure readings on
    your meter, you'll have to lift one leg of the component out of circuit. And in the case of SMD resistors,
    you'll have to remove them entirely, sorry to say that.
    Concentrate on the easiest to remove or lift a leg/s up first.

    If all good, then you're going to need to remove Q601 and Q603 and do a forward and reverse bias test
    on both of them.
    I have to say at this point, it isn't easy to remove a three legged surface-mounted device using just a
    soldering iron, but here's a fairly easy way of doing it:
    Place a blob of melted solder onto each pin of the transistor.
    Now alternating between the three elements with your iron as quick as you can, allow each ones solder to
    melt to the point that the transistor starts to move, then just slide it to one side away from other components
    and/or joints and let it cool.
    Lastly on this point, try not to heat the transistor for too long, as this may damage it.
    If you're finding it difficult at first, then allow it to cool, then try again. Keep repeating this, so you don't
    damage the bugger.
    You may encounter one problem, and that's if the transistor itself has been glued down at the factory. If so,
    it won't be easy to remove.
    The only way I know of how to do it with just a soldering iron, is to place a blob of solder onto the Collector of
    the device, leaving the iron in place, get a small thin sturdy piece of metal and try levering it up until one side
    lifts from the board. It may take a bit of pressure, as that glue is super strong.
    What ever you do, make sure your iron is constantly on the Collector. I Doubt you'll be able to melt or soften the
    glue though.

    OK, follow the next procedure when replacing or refitting the transistor:
    Using de-soldering braid, remove all the solder off each pad.
    Next, place a small blob of solder onto say the Base of the pad, then, with a set of tweezers, place the transistor
    onto the pads and heat the blob so the base pin moves into its proper place, at the same time, ensuring the
    Collector and Emitter pins are lined up as well. Make sure its laying flat as as possible.
    Once you're happy with its placement, solder the other pins, making sure all of the pads are wetted, but don't
    over-do it.

    OK, once the transistor/s are out here's a hint on measuring them:
    See the picture below for the pin configurations:



    Lets say you're going to measure Q601 (2SA1162), which is a PNP device.
    Set your meter to diode test.
    (1) - Place your negative probe onto the Base of the transistor and the positive probe on the emitter.
    You should get a reading of around .700 or something near that.
    (2) - Leaving the negative probe on the base, place the positive probe onto the Collector. You should
    again, get a reading similar to above.
    (3) - Now place your positive probe onto the Base and the negative probe on the Emitter. You should
    get an open circuit reading. Same reading when you place the negative probe onto the Collector.
    (4) - Next, place one probe (it doesn't matter which one), on the Collector, and the other on the Emitter.
    You should see an open circuit reading.
    (5) - Swap the probes, and once again, it should be open circuit.

    Now we need to do a punch-through test on the transistor. You pretty much repeat the above process,
    but there is no need to do Steps (1) and (2). They will be meaningless.
    Set you meter for its highest ohms range and proceed to do the punch-through.

    The same exact method will apply to measuring Q603 (2SC2712) NPN, except that your readings in step
    (1) and (2) will show that they will be open circuit.
    Its not until you do Step (3), that it should show a reading. It should be similar to the PNP test, around
    .700 or so.

    If you need to replace either or both transistors, these are recommended:
    2SA1162 ---> BC856A
    2SC2712 ---> BC846A

    The .700 readings, or the .607 reading on diodes just tells you how much voltage is required to bias the
    device. Therefore a .700 reading will indicate a 700mV forward conduction potential required.
    ALL readings I've indicated are just approximates and can vary quite a bit between devices.
    i.e. Schottky diodes usually have lower conduction requirements than standard diodes. Zener diodes
    should be higher than standard diodes.
    Same goes for transistors, though they are pretty much on par with each other.

    The above tests will allow you to determine if an unknown transistor is either NPN or PNP.
    By having the positive probe on the Base and getting readings on two of the other elements will tell you
    its an NPN. Positive probe to the P of the device.
    The reverse is true for PNP transistors.
    The above won't determine what pins are what, but at least it will determine its polarity, as well as identifying
    the base pin.
    So, when ever doing the above and you get two readings, then just look at what color probe is on the one
    pin that stayed where it was. That will give you its type, as well as the Base pin.

    As for FET's and MOSFET's, it is not possible to do static test as shown above. Here you would need a
    component analyzer to get any accurate readings. The best you can do is to determine if the component
    has gone short circuit.
    But when doing a short circuit test with the part, you need to first make sure you have no static in your
    body, then just place a wet finger across the three legs and then do your measurements.
    The reason for doing the wet finger test is to discharge any internal capacitance charge that may be present.
    Many a time I've measured brand new devices and in some cases they showed me that they were partially or
    completely shorted. This is where a wet finger helps.

    One last thing on transistors, they are NOT all made the same.
    Some have internal resistors which make it difficult to conduct a fairly conclusive test.
    Other transistors actually have two transistors in one, connected in parallel. These are high gain types and
    are usually called Darlingtons.
    There are many with internal diodes, mainly across the Collector/Emitter junctions, which are mainly seen
    in Horizontal Output transistors. The internal diode is required to dampen the collapsing magnetic field of a
    flyback transformer. Without it, the transistor would blow in micro-seconds.
    In the early days, they used a separate dampening diode, but due to technology improvements, they were able
    to integrate it within the device itself.

    Lastly, there is NO guarantee that doing the above measurements is totally foolproof. I have been caught out
    in the past, where I thought the device was good, yet when I replaced it, the set worked.
    Once we had such a device and we put it through a bevy of tests such as, its gain (βeta), set it up in a biasing
    circuit and it worked well and we also did curve tracing on it with its parameters being very close to what the
    datasheet info gave us.
    No reason for it to be faulty, but there you go.
    The only conclusion we could come to was the fact it didn't like high voltages. This transistor we tested was the
    blue cathode output transistor on the CRT board of a Sharp TV. Unfortunately when we bias tested it, we used low voltages
    only. Those output transistors require 150 plus volts for proper operation.

    So, my advise to anyone doing repairs, if in doubt, replace it. Provided you've done as much testing as possible.
    Otherwise it will only confirm that that's one component you know works.

    Please let me know how you get on, and sorry once again for the lengthy post.
    Regards,
    Relayer

    P.S. @e-music I'll try to answer you queries about the other set tomorrow. Sorry, but I've spent too much time on this post and
    I need to do stuff.
    Last edited by Relayer; Yesterday at 04:51.


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    •   AltYesterday, 04:38

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  8. #48
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    Re: Help needed to repair a Sony Trinitron KV-2165MT power failure

    Are you sure? Measured between negative C604 and pin 2?
    Yes, I'm pretty sure. I measured it dozens of times and just switched the power off now after re-soldering every solder joint at the PSU and almost 90% of others across the lower part of the board around the PSU, still the same result. If you want, I can take some photos and show you the results.

    When you measure the 115 V then your -probe should be on GND side C609
    Yes, that's what I did.

    Thanks

    - - - Updated - - -

    Hello Relayer,

    Thank you very much for your comprehensive diagnosis reply. I really appreciate the time you've taken to cover all these details and please take your time in getting back here. Of course, priority has to be for your own stuff, no worries there! :)

    I do need some time myself to get back to the set and do the tests and report the results back.

    Thank you again, and talk soon!



  9. #49
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    Re: Help needed to repair a Sony Trinitron KV-2165MT power failure

    Here is a very simplified version of a typical power supply like yours. The transistors Q1/2/3 and diode D2 is all in the STR power chip. The circuit needs the start-up current through R4 (R602/17 in your case). Once switching action starts, the feedback winding keeps it going. Output voltage will increase until the voltage feedback loop kicks in. When that happens, Q3 will start to shunt current away from the base. This will decrease the on-time of the main transistor, as can be seen in the collector current, which will prevent the 115 V from increasing any further.

    The diagram uses a common GND for simulation purpose only.

    Make sure R602/17 are the correct values.



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