Memorex MLT4221P stuck in standby

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  • gb77
    replied
    Re: Memorex MLT4221P stuck in standby

    yep - nice of them to confuse anyone without the service manual by marking the pcb 18v. i put the old caps back in & tested the p/s and it worked fine. since the mb died & i found out the tv is used as an all day security multi-cam monitor, the old p/s prolly is likely not gonna last that much longer in the heat either.

    Leave a comment:


  • retiredcaps
    replied
    Re: Memorex MLT4221P stuck in standby

    Put the original caps back in so it fits.

    Odd, that the 18V rail is working fine at 12V. What a waste of time chasing down that rail.

    Leave a comment:


  • gb77
    replied
    Re: Memorex MLT4221P stuck in standby

    mb voltage readings are same with a few pins .01-.03v difference.

    post 43 has my pic of the power supply with very large caps i refer to in my last post.

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  • gb77
    replied
    Re: Memorex MLT4221P stuck in standby

    new main board from shopjimmy is in and the tv is working again. put in old power supply with oversized caps & it works fine too with the "18v" line running @ 12v. should i put back the original caps, the large caps dont allow the heatsink plate to go back in flush - see the link for the plate on the right - reasons why or why not?

    https://www.shopjimmy.com/fsp-fsp271...wer-supply.htm

    i will take some voltage readings from the new mb to see if they differ from the old. since i have a good one, are there some other tests i can do on the old / new to compare and find the problem? for now i'm renting the mb for 30 days @ $20 - thanks for any help

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  • gb77
    replied
    Re: Memorex MLT4221P stuck in standby

    thanks for the help so far retiredcaps - i'm thinking to 'buy/rent' a mainboard from shopjimmy for ~$97/20 (return charge) to see if a replacement will bring any joy. if there are any precautions you would suggest before swapping them, i'd appreciate that.

    if anyone else has suggestions i'd be glad to hear them too. i looked over my old post about a samsung that ran a 5v, (11.8 on) a 12v & 24v from the p/s. which makes me wonder if the board markings of 18v dont necessarily mean all versions of the p/s run 18v.

    enjoy the olympics - i will too - 2 tvs at a time - or 3 for a while if i fix this one too.. lol

    Leave a comment:


  • retiredcaps
    replied
    Re: Memorex MLT4221P stuck in standby

    Originally posted by gb77
    thanks for any ideas on what to check next.
    I'm out of ideas right now. My brain needs a break for a while and I think the watching the Olympics will help me do that.

    Leave a comment:


  • gb77
    replied
    Re: Memorex MLT4221P stuck in standby

    still looking for some help here. since i dont have the remote, and the power switch doesnt do anything, i checked voltages going to the power & other buttons. all read 0. checked the inverter boards, and both are getting 24v & have good fuses, with I-PWM @ 3.28v. thanks for any ideas on what to check next.

    Leave a comment:


  • gb77
    replied
    Re: Memorex MLT4221P stuck in standby

    got the chips - decided to triple check what was going on, noticing a couple more identical AS1117L chips to the left of the 78T05AL. figured i'd measure them too, getting 2.04 / 3.29 / 4.99 & 2.04 / 3.28 / 5.02 which matches the 1.25 bump. took another measurement of the suspect chip, and found i must have made a transcription error ( & failed to notice .6 =\= .06 on my double check) as it does measure .06 on pin1 and not 0.6 - so it checks out within .01v. so on to the next line of inquiry i hope - for now i have some spare chips! thanks for your next ideas.

    Leave a comment:


  • retiredcaps
    replied
    Re: Memorex MLT4221P stuck in standby

    I use a non temperature controlled heat gun on low heat to remove these types and I use Kapton tape to cover all the surrounding components so they are not damaged by the heat from the heat gun. With this method, it takes about 30 seconds to remove.

    Leave a comment:


  • gb77
    replied
    Re: Memorex MLT4221P stuck in standby

    ok, ordered 3 samples - will have to practice similar smt soldering while waiting

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  • gb77
    replied
    Re: Memorex MLT4221P stuck in standby

    https://cdn.badcaps-static.com/pdfs/...9aecb4a8ce.pdf

    addendum pg 5 shows TI will send out samples of this one. i got samples from TI or someone maybe 10 yrs ago. looks like i need to set up an account

    https://focus.ti.com/tipass/docs/reg...?&actionId=368

    is it still simple where i can say i'm a student or is there some verification / hassle now? any suggestions?

    Leave a comment:


  • retiredcaps
    replied
    Re: Memorex MLT4221P stuck in standby

    The capacitors just above that suspect voltage regulator looks like a crop circle in the farmers field. I have never seen that before.

    Leave a comment:


  • retiredcaps
    replied
    Re: Memorex MLT4221P stuck in standby

    Originally posted by gb77
    A1
    AS1117L
    80737 92
    0.6 1.3 3.29

    same as previous
    0.25 1.49 3.29
    Okay, we may have found the problem. The AS1117L is an adjustable voltage regulator. The correct output for pin 2 (middle) is based on this calculation:

    DC V of pin 1 + 1.25V = output of pin 2.

    As you can see, the bottom voltage regulator is

    0.25 + 1.25 = 1.50 (you have 1.49 which is close enough).

    The first voltage regulator is

    0.6 + 1.25 = 1.85 whereas you measured 1.3 (more than 30% off).

    So confirm that the readings on pin 1 and 2 are 0.6 and 1.3 respectively. If yes, that voltage regulator is likely bad. I say likely because there may be cap that is pulling down the voltage on pin 2, but in 90% of the cases I have seen, it is likely the voltage regulator.

    This replacement should work. You might want to get 2.

    http://www.digikey.com/product-detai...98-1-ND/705738
    Last edited by retiredcaps; 07-20-2012, 12:41 AM.

    Leave a comment:


  • gb77
    replied
    Re: Memorex MLT4221P stuck in standby

    if for some f-d up reason the 18v line was supposed to run @ 11.8 for this tv.. what would be the next steps to see what was wrong?

    Leave a comment:


  • gb77
    replied
    Re: Memorex MLT4221P stuck in standby

    searching mouser & digikey for 78t05 yields some results, but nothing in stock - showing 3A 5v max output

    http://www.datasheetdir.com/78T05+Regulators

    shows 0.5A - clik link to datasheet pdf - the ---05 on the chip indicates output is 5v

    http://www.datasheetdir.com/78T05+download

    looks like 11.77 is the input v & 4.94 is output

    if i disconnect 18v load from p/s the 11.77 goes to 0
    Last edited by gb77; 07-19-2012, 09:13 PM.

    Leave a comment:


  • gb77
    replied
    Re: Memorex MLT4221P stuck in standby

    from top to bottom of the ones you circled

    utc
    78T05AL
    05 UGBS
    11.77 0 4.94

    this one has a glob of glue on it
    1084
    PE
    507D2
    2.05 3.29 5.0

    A1
    AS1117L
    80737 92
    0.6 1.3 3.29

    same as previous
    0.25 1.49 3.29

    2 more on left side of mainboard (you can see them in attachment https://www.badcaps.net/forum/attach...2&d=1339903244 )

    A1
    AS1084S3
    A0723
    1.37 2.62 5.01

    1084
    PE
    507D2
    2.04 3.28 5.01

    that 1st one has the 11.8v going on - any significance?

    Leave a comment:


  • retiredcaps
    replied
    Re: Memorex MLT4221P stuck in standby

    Originally posted by gb77
    ok - the real fun begins. friend comes up with $ to buy the p/s from shopjimmy. it arrives & i install it, connecting only the 5v load - the 18v line is @ 11.8v (24 is 24) on the new one too. disconnect power, plug in the 18 & 24 v connectors, connect power and tv remains in standby.

    any ideas?
    Okay, assuming the shopjimmy board is good, let's check the main/logic board. I circled 4 voltage regulators. There may be more, but that is all I can see in the photo.

    To test a voltage regulator (circled in red),

    1) Set your multimeter (if manual range) to 20V DC.

    2) Put your black probe on a ground screw (circled in black). Leave it there the entire time. This is your ground.

    3) Put your red probe on each of the pins including the "cut" pin, but ignore the "fat" tab. The fat tab is "up" or "north". Number the pins left to right.

    4) You should have 3 readings per regulator.

    5) Report them like so along with the part number (include all lines on the IC) of the IC.

    U100
    AS1117-33
    pin 1 = 0.0
    pin 2 = 3.3
    pin 3 = 5.0
    Attached Files

    Leave a comment:


  • gb77
    replied
    Re: Memorex MLT4221P stuck in standby

    ok - the real fun begins. friend comes up with $ to buy the p/s from shopjimmy. it arrives & i install it, connecting only the 5v load - the 18v line is @ 11.8v (24 is 24) on the new one too. disconnect power, plug in the 18 & 24 v connectors, connect power and tv remains in standby.

    any ideas?

    Leave a comment:


  • retiredcaps
    replied
    Re: Memorex MLT4221P stuck in standby

    Originally posted by gb77
    have a look at the large Illinois Capacitor surplus caps in place.
    1) Geez, those are huge.

    2) The inductor right by those two new huge caps is partially covered in white glue. A long shot, but try resoldering the two solder joints on the back of the inductor.

    3) My spatial mapping skills are not the greatest so I can't tell if the 4 circled transistors are part of the 18V rail or not, but test each one to see if they are shorted between pins 1-2, 1-3, and 2-3. Report all your readings.

    4) You also have 8 SMD diodes in that area. You might as well test them all and report the 16 readings (2 per diode).
    Attached Files

    Leave a comment:


  • gb77
    replied
    Re: Memorex MLT4221P stuck in standby

    replaced the caps, and readings are still the same. have a look at the large Illinois Capacitor surplus caps in place. thanks for your ideas. maybe you have some more? i sent a request to the power supply maker for a schematic telling them i was troubleshooting why the 18v line was only at 11.8v. dunno if such places ever respond to such requests.
    Attached Files

    Leave a comment:

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