Memorex MLT3221 - No Power

[johnnieboy2]

Re: Memorex MLT3221 - No Power

If I had to bet, I'd stick with that number...but, possibly the '6' could be a '5'. It's not hard to read with a 'glass', but there is a small dot to the lower left of the first number that could make a 5 look like a 6. The only other number that could be confusing is the '7' which could be a '1', but it's slanted so I highly doubt that.

[johnnieboy2]

Re: Memorex MLT3221 - No Power

I managed to get a pic of the IC in question, excuse the quality please.

[johnnieboy2]

Re: Memorex MLT3221 - No Power

I managed to get a pic of the IC in question, excuse the quality please. It's got a 'blue star' just below the IC, number is definitely correct...maybe a 'house' number? Sorry for the double post.

[johnnieboy2]

Re: Memorex MLT3221 - No Power

[QUOTE=johnnieboy2;193033]I managed to get a pic of the IC in question, excuse the quality please. It's got a 'blue star' just below the IC, number is definitely correct...maybe a 'house' number...unless the '6' is a 'G'? Sorry for the triple post.

[ecking767]

Re: Memorex MLT3221 - No Power

this may be the datasheet you need.



hope this help

ecking767

[PlainBill]

Re: Memorex MLT3221 - No Power

this may be the datasheet you need.



hope this help

ecking767

ecking, Thanks. It'll be fairly easy to verify the pinout.

johnnieboy2, I've marked up the picture of the bottom of the power supply. The point circled in black is the negative terminal of the large cap. It is also the 'hot' ground. I've also marked pins 1, 3, 4, and 6 of the SMPS controller.

With the TV disconnected from AC power, measure the resistance from hot ground (circled in black) to pin 1 of the SMPS controller (IC2). It should be very low - essentially zero.

Next, plug in the power cord and carefully measure the voltage from hot ground to pins 1 through 6 of IC2. Report the readings.

PlainBill

[johnnieboy2]

Re: Memorex MLT3221 - No Power

I had to take a nerve pill after I measured the voltages...do you know how many IC's I've blown trying to measure voltages on pins on IC's 3X that size...Whew!

Anyway:

resistance from hot ground to pin 1 of the SMPS controller (IC2) -zero
voltage from hot ground to pin1 = 0vdc
voltage from hot ground to pin2 = 0-5vdc
voltage from hot ground to pin3 = 0-2vdc
voltage from hot ground to pin4 = 0vdc
voltage from hot ground to pin5 = 9-14vdc
voltage from hot ground to pin6 = 0-.4vdc

I didn't see or smell smoke, hope that's a good sign!

[PlainBill]

Re: Memorex MLT3221 - No Power

I had to take a nerve pill after I measured the voltages...do you know how many IC's I've blown trying to measure voltages on pins on IC's 3X that size...Whew!

Anyway:

resistance from hot ground to pin 1 of the SMPS controller (IC2) -zero
voltage from hot ground to pin1 = 0vdc
voltage from hot ground to pin2 = 0-5vdc
voltage from hot ground to pin3 = 0-2vdc
voltage from hot ground to pin4 = 0vdc
voltage from hot ground to pin5 = 9-14vdc
voltage from hot ground to pin6 = 0-.4vdc

I didn't see or smell smoke, hope that's a good sign!

I hear you. I'm working on 4 Mindstorm NXTs soldering parts much smaller than a grain of rice.

Well, the voltages indicate there is some activity on the SMPS controller. Possible causes are a bad startup cap or problem with the tertiary winding. Because of the lack of activity on pin4, it's probably not a shorted output diode.

PlainBill

[johnnieboy2]

Re: Memorex MLT3221 - No Power

Hopefully my replacement caps will be in very soon. Thanks again PlainBill for hanging in there with me.

[johnnieboy2]

Re: Memorex MLT3221 - No Power

Well, after about an hour of careful soldering...looks like I got a 'trick' this Halloween night...seems to have changed nothing. No LED lit on P/S board, steady blinking lED on lower right front of TV, no 'noise' of any kind. Sort of disheartening, but I do appreciate your help and advice given...all caps replaced. I did have two 10uf @ 450v and a 10uf @ 50v caps left over from the kit I ordered, but no place on the board for them, curious, but I guess they applied to a different revision board.

You mentioned tertiary winding, where and can it be checked easily?

[PlainBill]

Re: Memorex MLT3221 - No Power

Well, after about an hour of careful soldering...looks like I got a 'trick' this Halloween night...seems to have changed nothing. No LED lit on P/S board, steady blinking lED on lower right front of TV, no 'noise' of any kind. Sort of disheartening, but I do appreciate your help and advice given...all caps replaced. I did have two 10uf @ 450v and a 10uf @ 50v caps left over from the kit I ordered, but no place on the board for them, curious, but I guess they applied to a different revision board.

You mentioned tertiary winding, where and can it be checked easily?

Darn!!! I wish I had a way to edit PDFs - or at least convert a page to a jpg.

Pin 5 of the SMPS controller is Vcc. It gets power via two paths - through avery high resistance from the + side of the mains filter cap (the big one), and from a winding on the SMPS transformer. For some reason I'm unable to download the datasheet; and while your pictures are very good, I can't see traces that run under ICs. All I can suggest is to identify where pin 5 comes out from under IC2.

PlainBill

[retiredcaps]

Re: Memorex MLT3221 - No Power

Darn!!! I wish I had a way to edit PDFs - or at least convert a page to a jpg.

Hit the Alt and Printscreen (copy screen into buffer) key at the same time while the pdf is displayed. Then bring up your favourite graphics program and press Ctrl-V (paste).

[johnnieboy2]

Re: Memorex MLT3221 - No Power

Hit the Alt and Printscreen (copy screen into buffer) key at the same time while the pdf is displayed. Then bring up your favourite graphics program and press Ctrl-V (paste).

Out of curiosity I tried this and it did not do anything to bring up any of my graphics programs. I use a free program MWSNAP3 to capture any screen area and it works great. I can save the snapshot and load it into my graphics program.

[PlainBill]

Re: Memorex MLT3221 - No Power

Control - Print Screen didn't work, but MWSnap did the trick.

The area circled in yellow is the run supply for the SMPS controller. The coil is actually part of the main SMPS transformer.

PlainBill

[johnnieboy2]

Re: Memorex MLT3221 - No Power

what should my voltage be? Earlier I reported 9-14vdc on this pin.

[PlainBill]

Re: Memorex MLT3221 - No Power

what should my voltage be? Earlier I reported 9-14vdc on this pin.

There are several parameters to consider. The absolute maximum voltage allowed on that pin is 30 volts. The normal operating range is 10 - 30 volts. The controller starts when the voltage on that pin rises above 15 volts and stops if it drops below 7.5 volts (+- 1 volt on the last two parameters).

Those readings suggest the controller is starting, but the run power is not maintaining operation. There are a number of possible causes. One is if the startup cap is bad. If you replaced it, that is unlikely to be the cause. Another (rare) cause is a bad winding on the smps transformer. A bad diode, either on the run power circuit (open) or on one of the outputs of the SMPS transformer (shorted), or a shorted load would also cause the problem.

PlainBill

[johnnieboy2]

Re: Memorex MLT3221 - No Power

All the EC 's were replaced on this board except for the large one which was ruled out early on as the problem. Can I check the transformer windings with an ohm meter in circuit, AND is the possible shorted load on this same board or another one? I'll check pin 5 voltage again.

[PlainBill]

Re: Memorex MLT3221 - No Power

All the EC 's were replaced on this board except for the large one which was ruled out early on as the problem. Can I check the transformer windings with an ohm meter in circuit, AND is the possible shorted load on this same board or another one? I'll check pin 5 voltage again.

You can check the transformer windings in circuit. They will all read a very low resistance. The 'shorted load' can be anywhere. This design is a little unusual; there is only 1 SMPS which is always on. Disconnect the other boards and see if the power supply works.

PlainBill

[johnnieboy2]

Re: Memorex MLT3221 - No Power

Thanks, I'll check it...can you tell me what transformer it is...where? I didn't know if I might damage anything ELSE if I unloaded the P/S and powered on. Again, anybody need any parts if this doesn't work out in the end...which might be soon approaching?

[PlainBill]

Re: Memorex MLT3221 - No Power

Thanks, I'll check it...can you tell me what transformer it is...where? I didn't know if I might damage anything ELSE if I unloaded the P/S and powered on. Again, anybody need any parts if this doesn't work out in the end...which might be soon approaching?

I've marked up the picture. The lines in yellow indicate the path.

PlainBill