Memorex MLT4221P stuck in standby

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

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.

TWO retiredcaps' bonus points for showing 4 multimeters. The BluePoint would be your "best" multimeter to use. It is mainly geared towards automotive technicians, but can be used for everyday applications.

I was thinking your fluctuatinig readings may be due to a lack of proper ground? If you have to turn your board upside down to take measurements, you may not have a ground?

Let's try this.

1) Put your power board back into the TV and secure it with all the screws in place.

2) Now measure the DC voltage of the large filter C1.

3) Put your red probe on the positive leg and black probe on the negative leg. Careful, this is high voltage as it should read about 165V DC.

4) What is your reading and is it stable?

5) Try this for your 2 multimeters plus the BluePoint. Before trying the BluePoint on the large cap, try it out measuring some AA batteries first to make sure it works.

[gb77]

Re: Memorex MLT4221P stuck in standby

budm - the rectifier you suggest to change is an ON MBR2045CTG - is it possible that is the only problem? it's about $1 ..

http://www.mouser.com/Semiconductors...0A+45V&FS=True

got a decent pic of the 18v area on back of p/s.

retiredcaps - when i took readings, i used a jumper from the board's ground clip/screw hole to the ground strap screw the power cord plug is grounded to. i'll put it back in and try your suggestion. any ideas for creating leads for the bluepoint?

[gb77]

Re: Memorex MLT4221P stuck in standby

got hopeful results from MMs - black (GB) & yellow (MA - used 14ga copper loop into leads) - the bluepoint measure a couple 9v batts same as GB, but fried when attached to leads from C1 with p/s under load.

MA . . . . . . GB
164.7 . . . . 164.8-165 . . no load
407 . . . . . .405-407 . . . load (5,18 & 24v leads connected to p/s)

so it seems the GB is getting good reads where the peak value is closer to reality. is it worth remeasuring IC2 with MA?

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

got hopeful results from MMs - black (GB) & yellow (MA - used 14ga copper loop into leads) - the bluepoint measure a couple 9v batts same as GB, but fried when attached to leads from C1 with p/s under load.

MA . . . . . . GB
164.7 . . . . 164.8-165 . . no load
407 . . . . . .405-407 . . . load (5,18 & 24v leads connected to p/s)

so it seems the GB is getting good reads where the peak value is closer to reality. is it worth remeasuring IC2 with MA?

1) Sure, try remeasuring IC2 with the MA.

2) It looks like the big cap and PFC are working. So it is possible that just the 18V rectifier is bad. If you are going to place an order, you might as well get replacement caps to ammortize the $8 CDN shipping/handling charge.

3) What do you mean fried the BluePoint? It is rated up to 600V. Does it still measure AA batteries okay?

[gb77]

Re: Memorex MLT4221P stuck in standby

fried the BluePoint = something popped & burned/scorched its pcb. it was a freebie, so i'm not gonna worry about it since the MA seems good.

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

fried the BluePoint = something popped & burned/scorched its pcb.

Maybe that is why your friend left it there?

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

fried the BluePoint = something popped & burned/scorched its pcb.

PS. If you are going to toss it in the garbage, let me know (via PM). I would like to take a look at it internally. Multimeters, as you can tell, is a hobby of mine now.

[gb77]

Re: Memorex MLT4221P stuck in standby

taking another shot @ IC2 (no load) - seems the V still goes up and down a bit on pins 1 & 2. also, the V on pin4 (with no other connection) jumped around between .1 to 2.5 (mostly between .4 & .9) after touching it the first time, or another pin. so not sure if this is normal, or MM problem (should i watch this more closely to get a timing of the jumps to report back?) holding ground to pin4, pin1 would drop V by .3 to .5, pin2 varied below 1v (nothing like the 3.8 before). pins 3 5 6 8 gave stable measurements.

. . . . . try1 /try2 /try3
Pin1: .50-.52 /.37-.41 /.56-.61
Pin2: varied below 1.0
Pin3: .0 /.0 /.0
Pin4: --
Pin5: .0 /.0 /.0
Pin6: 9.57 /9.57 /9.57
Pin7: no change in v - pin not used?
Pin8: 165.3 /165.3-165.4 /165.2

i also noticed the grounds on the power leads don't have continuity with chassis ground (the metal tab on bottom left screw hole in 1st post pic), tho they have continuity with each other. any issue?

[gb77]

bluePoint got burned

enjoy the view

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

. . . . . try1 /try2 /try3
Pin1: .50-.52 /.37-.41 /.56-.61
Pin2: varied below 1.0
Pin3: .0 /.0 /.0
Pin4: --
Pin5: .0 /.0 /.0
Pin6: 9.57 /9.57 /9.57
Pin7: no change in v - pin not used?
Pin8: 165.3 /165.3-165.4 /165.2

Okay, the above is more in line with what I expected. Much less fluctuation and pin 6 (VCC) and pin 8 (HV) are stable.

Since they are stable, I think you should replace that 18V rectifier and retest after you put it in.

i also noticed the grounds on the power leads don't have continuity with chassis ground (the metal tab on bottom left screw hole in 1st post pic), tho they have continuity with each other. any issue?

I'm not 100% sure what you are asking here.

[retiredcaps]

Re: bluePoint got burned

enjoy the view

Wow, it looks like one of the tracks peeled completely and you can see the damage on the backside of the case.

This multimeter is pretty user friendly too. Only two input sockets so there should be no user error with putting the wrong probe in the wrong socket (i.e into amps socket). It is also CAT III rated to 600V which you can believe unlike a lot of junk found on ebay with fake CAT ratings stamped on the front.

Notice those deep ridges on the inside of the case. It is designed to be deep to keep any "explosions" inside the case.

This is one reason I always caution people when they are about to measure high voltage components.

[gb77]

Re: Memorex MLT4221P stuck in standby

when you say retest after replacing rectifier, do you mean measure 18v output & other stuff & report back before reconnecting the p/s to load if 18v checks good?

let me say it more precisely then..
the ground pins from cns1,2,3,4 (what i called the power leads) don't have continuity with board (chassis) ground (metal tab around screw hole @ bottom left of p/s in 1st pic in 1st post). are they supposed to?

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

when you say retest after replacing rectifier, do you mean measure 18v output & other stuff & report back before reconnecting the p/s to load if 18v checks good?

I mean order a new 18V rectifier put everything back together and retest.

let me say it more precisely then..
the ground pins from cns1,2,3,4 (what i called the power leads) don't have continuity with board (chassis) ground (metal tab around screw hole @ bottom left of p/s in 1st pic in 1st post). are they supposed to?

Is the bottom left hand screw hole screwed into the chassis?

[gb77]

Re: Memorex MLT4221P stuck in standby

Is the bottom left hand screw hole screwed into the chassis?

yes, it has continuity with the power cord ground

thanks for all your help

[gb77]

Re: Memorex MLT4221P stuck in standby

hi - i've got the new rectifier & time to test, so i popped out the old one. took some readings & would like to know if they are meaningful. would like feedback or other tests to try before putting new one in.

resistance R/L
new 358/359 old 369/371
(no continuity for new & old in wrong direction)
V drop (diode setting)
new 165/166 old 166/167

they seem about the same - would the old one likely be bad still?

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

they seem about the same - would the old one likely be bad still?

Although your readings indicate that there is no significant difference between the two, the old could still be bad.

A multimeter can only test so much in "standalone" mode. Schottky rectifiers need to be tested "in circuit".

[gb77]

Re: Memorex MLT4221P stuck in standby

new rectifier is in place - all basic measurements remain the same 5v=5v, 24v=24v, 18v=11.8v, main cap is still 164 / 407. havent tried measuring ic2 again. bud asked about readings with/out load - with no load 5v=5v and 24 & 18 =0 - with 5v load connected 24v=24v & 18=11.8v. normal behavior?

what is feeding voltage to the rectifier if it's not the problem?

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

what is feeding voltage to the rectifier if it's not the problem?

It could be bad capacitors dragging down the voltage on the rectifier? My guess would be CS8 and CS23. Measure the DC voltage across both of those caps and report what you find.

[gb77]

Re: Memorex MLT4221P stuck in standby

cs8 & cs23 caps read 11.8 - same as before. any other cheap parts that i could replace that affect 18v line? it was mentioned above that the same xformer supplies 18 & 24v - could part of it be bad?

i'm going by a local electronics surplus tomorrow - can i use some range of cap for testing purposes if i cant find a 680uF 25v to match exact?

[retiredcaps]

Re: Memorex MLT4221P stuck in standby

cs8 & cs23 caps read 11.8 - same as before. any other cheap parts that i could replace that affect 18v line?

Without a schematic, I can't tell. For testing purposes, you can get some "surplus" caps and if it fixes the problem, then get "proper" low ESR caps.

it was mentioned above that the same xformer supplies 18 & 24v - could part of it be bad?

In 2+ years, I have yet to see a transformer on the power supply go bad. It doesn't mean yours is 100% good, but the likelihood is low.

i'm going by a local electronics surplus tomorrow - can i use some range of cap for testing purposes if i cant find a 680uF 25v to match exact?

Yes, if you can't find the exact capacitance, get a 470uF and/or 820uF. You can go up in voltage like 680uF 35V.