Memorex MLT4221P stuck in standby

[gb77]

Re: Memorex MLT4221P stuck in standby

should i take 470 - 820 as a range? or do you mean i should find 2 caps that add up to something near 1360 total?

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

should i take 470 - 820 as a range? or do you mean i should find 2 caps that add up to something near 1360 total?

If you can't get two 680uF, then get one 470uF and one 820uF so the total is close to the original.

[gb77]

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.

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

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).

[gb77]

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?

[retiredcaps]

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?

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

[gb77]

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?

[gb77]

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

[gb77]

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?

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

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

[retiredcaps]

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.

[gb77]

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?

[gb77]

Re: Memorex MLT4221P stuck in standby

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

[retiredcaps]

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.

[gb77]

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.

[gb77]

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.

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

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.

[gb77]

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

[gb77]

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

[gb77]

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.