Memorex MLT4221P stuck in standby

[gb77]

with active inputs to vid2, svid & YPbPr2, powering the tv gets the standby ring to go red. but pushing power or any other button on tv (i dont have remote) changes nothing - red ring, no audio or video. a flashlight has no effect on the screen (no menu or anything). so i popped off the back cover to have a look.

all the caps look good/flat & i didnt see any evidence of leakage or burning. fuse F1 on power supply tested good, with power on have 120v thru the fuse.

i took voltage readings from the p/s - pic 1 (my multimeter battery is a bit weak, not sure of any effect):
cns1 - yellow 5v - red 4.6v (0/F)
cns2 - brown 11.8v (18v)
cns3 - blue & red 24v
cns4 - red 24v

hopefully the low reading @ 18v will lead to a simple solution. i dont have tech beyond a multimeter to test components. so i guess i'm a tinkerer, not anything more, and hoping your ideas will bring some alternatives for a solution. pics 2 & 3 are of the mainboard.

thanks for your help.

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

(my multimeter battery is a bit weak, not sure of any effect):

We just had a discussion on this subject and YES it matters depending on the make and model of the multimeter. If the battery low icon is showing, you could be getting incorrect readings (like my new old used Fluke 27). I suggest you put in a new battery and remeasure.

[gb77]

Re: Memorex MLT4221P stuck in standby

i found my other multimeter (both are cheap $15 models, but this one has new 9v battery, while other one has older battery, but no batt warning) - but nearly the same result - i used 20vDC scale for 3 of them.

readings this time were:
cns1 - yellow 5.06v - red 4.63v (0/F)
cns2 - brown 11.84v (18v)
cns3 - blue & red 24.1v
cns4 - red 24.1v

[budm]

Re: Memorex MLT4221P stuck in standby

Are the connectors labeled with voltages? this chassis is the same as used in Polaroid TV.
So the 18V output is reading 11.84V? That will be strange since the 24Vdc supply is generated by the same transformer as the 18Vdc supply section, so I expect the 24Vdc output will be low also.

[gb77]

Re: Memorex MLT4221P stuck in standby

yes, cns1 labeled 5v @ yellow wire, the red wire is labeled 0/F. cns2 - 18v (got 11.8 3 times measured), cns3&4 24v - all the red and blue leads show the same 24v.

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

I don't have schematic for this power supply so I'm guessing based on your picture.

If CN2 is the middle connector, then I'm guessing that the dual diode is mounted onto the heat sink just to the left.

If correct, try measuring the output from the diode and see if it is 18V. The two caps just to the right of the diode may be on the 18V rail. If yes, see if the voltage across those two caps (which might be 25V or 35V rated caps) are 18V or not.

[gb77]

Re: Memorex MLT4221P stuck in standby

the center lead of the dual diode also reads 11.8v - the outer leads vary when contacted but seem to settle on -.04v after a bit. the + leads from the caps (both 25v 680uF) are also 11.8v (measure from the back side of the board.

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

Another TV as budm alluded to uses this same power supply. See

https://www.badcaps.net/forum/showthread.php?t=16434

Is IC2 the same part number as the Memorex?

If yes, measure the DC voltage IC2 for all pins wrt to its ground pin. I just want to verify some readings.

[budm]

Re: Memorex MLT4221P stuck in standby

Spec:
http://www.fspgroupusa.com/fsp2714f02/p/764.html
Looks like we are going to need good clear pictures of the bottom side of the board to look at the area of the 18Vdc section.

[gb77]

Re: Memorex MLT4221P stuck in standby

let me know if the pics posted above are clear enough, thanks

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

let me know if the one posted above is clear enough, thanks

I think we need a clear shot of the section in yellow.

[budm]

Re: Memorex MLT4221P stuck in standby

From what I can see, there 3 feedback signals in the 18/24VDC outputs that are used to regulated the output, since I do not have the diagram for this power supply, I would try replacing the rectifier for the 18V section, the whole thing does not clear yet why it is regulating the 24Vdc OK but not the 18Vdc, one possibility is that the 24Vdc is not loaded due to the backlights are not running, it may drop under load.
What happen if you remove the 18V connector so it will not have the load? Do you get 18v?

[gb77]

Re: Memorex MLT4221P stuck in standby

i checked thread 16434 & that looks the same as mine. IC2 is
230D6
PALS
so 2nd part of label is different. following that thread, using pin4 as ground/black, starting from pin1 (counterclockwise) the readings go up and down in the following ranges (don't know if my cheap multimeter is giving good readings or i'm doing it wrong, so treat me like a n00b, i don't mind the help)
Pin1: .39 to .44
Pin2: 3.81 to 3.88
Pin3: .01 to -.01
Pin4: -- with ground/black lead only connected :: .55 to .60
Pin5: .01 to -.01
Pin6: 8.56 to 9.22
Pin7: .28 to .36
Pin8: 160.9 to 163.3

removing the 18v load brings the readings up to 11.88 from 11.83

i got a bunch of blurry pics - any suggestions for getting clear shots by hand? the pic in that other thread is accurate

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

starting from pin1 (counterclockwise) the readings go up and down in the following ranges (don't know if my cheap multimeter is giving good readings or i'm doing it wrong, so treat me like a n00b, i don't mind the help)
Pin1: .39 to .44
Pin2: 3.81 to 3.88
Pin3: .01 to -.01
Pin4: -- with ground/black lead only connected :: .55 to .60
Pin5: .01 to -.01
Pin6: 8.56 to 9.22
Pin7: .28 to .36
Pin8: 160.9 to 163.3

I'll have to check the datasheet to see if that is okay or not, but fluctuations are never good.

Does your multimeter have a fresh new battery in it? An old tired battery might give bad readings.

i got a bunch of blurry pics - any suggestions for getting clear shots by hand?

Wait until tomorrow when the sun comes out. Take the board to a window ledge and put your camera on macro mode with no flash.

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

What is the part number of that 8 pin IC in budm's marked up diagram where it says P/N?

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

(don't know if my cheap multimeter is giving good readings

Post a picture of it for one retiredcaps' bonus point.

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

BTW, it is always best to reply directly to a question in a new post rather than edit an old previous post. Most of us usually NEVER re-read the old previous post even if it has been edited.

[gb77]

Re: Memorex MLT4221P stuck in standby

P/N
ICS1
AS358M-E1
739R84

2 MMs for the price of 1 - the black has a new(er) batt, yellow is older.

[budm]

Re: Memorex MLT4221P stuck in standby

OK, it is a dual Op-amp: http://pdf1.alldatasheet.com/datashe...AS358M-E1.html
Probably used for comparator circuits of some sort.

[gb77]

Re: Memorex MLT4221P stuck in standby

the 2 9v batts i have measure each other as 9.03v / 8.92v

have a couple MMs left by old roommate - no leads, no battery (9v) so don't know if they even work. if one might be useful, can you point me to some generic manual on how to use it? thanks.