Anyone familiar with the Akai LCD3701AD?

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

Once we figure out what's wrong and why the TV isn't working, do you guys think I should recap the entire board? The PSU and the main board? Maybe even the DVD board?

This customer is my Doctor and he pays really good. Normally I fix his PCs but he brought me this and we really need the cash. My wife doesn't think we'll have enough once she takes paternity leave. Thanks.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

I'd like to add when the backlight is kicking on and right back off, the PSU makes a clicking noise. However, when I tested the PSU outside the TV, it made the same clicking noise. The clicking noise seems to be synced with the flashing of the backlight. Not sure if that's relevant or not. It almost sounds like it's coming from one of the transformers.

[budm]

Re: Anyone familiar with the Akai LCD3701AD?

Here's a copy of the service manual. The schematics start on page 17 I believe (16 is written on the bottom page, but in Adobe, it says page 17).

On that page, on the right hand side, I can see:

8202UP3_1 HIGH :POWER OFF
8202UP3_1 LOW :POWER ON

In that section, I see the transistor Q21. I should see if voltage is getting to Q21, right? But it seems there's something else going on with it blinking the way it blinked. I guess it could have been a bad connection, the way I had it hooked up....but to blink the way it did, that would be one weird bad connection. Good connection for a second, bad connection for a second, good connection for a second, bad for a second, etc. I doubt it was a bad connection.

See attached picture. If you force on the PS-ON pin of the power supply and the PS-ON wire to pin 6 of J23 of the main board is not connected during the force on of with resistor, the power supply should comes on and stays on solid.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

See attached picture. If you force on the PS-ON pin of the power supply and the PS-ON wire to pin 6 of J23 of the main board is not connected during the force on of with resistor, the power supply should comes on and stays on solid.

I forced on the PS_ON pin of the power supply. I left the wire to pin 6 of J23 in but I removed the other end of the wire, the end where it goes into the PSU (because that's where I was jumping it). I just left the pin 6 wire on J23 dangling safely off to the side. This wouldn't make a difference though, right?

That wire would just act as a longer pin, the TV shouldn't be able to detect that it's there...

Do you have any suggestions what would make the TV blink on and off like that after forcing PS_ON to high? I used the 1Kohm resistor as suggested. I tried a second time, a different way, to make sure it wasn't a bad connection, same symptoms. Just blinks on and off, on and off.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

Budm,

I looked at the drawing you provided. I have a few questions though. What exactly are the lighter redish coloured labels? For example, the one that says SB33B and the one that says 8202UP3_1? Are they just labels? I was thinking the SB33B just means on this schematic, we connect to another schematic at point SB33B. If that's the case, what's the 8202UP3_1 then? Thanks.

The base of that 2N3904 is measuring 0.721VDC. 0.65VDC is the base-emitter saturation value, so that means that transistor is on, which makes the TV stay off, right? I'm just trying to learn all this. I appreciate the help.

**EDIT: I think that 8202UP3_1 means it goes to the MT8202 IC. Not sure what the UP3_1 means yet, I'm guessing it determines what pin it goes to on the IC. Perhaps that MT8202 is bad and needs to be replaced?

[budm]

Re: Anyone familiar with the Akai LCD3701AD?

Budm,

I looked at the drawing you provided. I have a few questions though. What exactly are the lighter redish coloured labels? For example, the one that says SB33B and the one that says 8202UP3_1? Are they just labels? I was thinking the SB33B just means on this schematic, we connect to another schematic at point SB33B. If that's the case, what's the 8202UP3_1 then? Thanks.

SB33B = 3.3V power supply. Yes, it is connected to other circuit that has SB33B.
5VSB = 5V power supply

8202UP_1 is the schematic NETLIST named '8202UP_1'. Yes, it is also connected to other circuit that has that same NETLIST name.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

It appears to be a BGA component, so I don't think it'll be that hard to replace, if it is bad. Just finding one, that might be an issue. What do you think Budm? Try finding a replacement MT8202 BGA component, remove the current one, replace it with a new one and see if the TV works?

[budm]

Re: Anyone familiar with the Akai LCD3701AD?

'The base of that 2N3904 is measuring 0.721VDC. 0.65VDC is the base-emitter saturation value, so that means that transistor is on, which makes the TV stay off, right? I'm just trying to learn all this.'
That is correct, so what ever drive that transistor it is stuck ON and causes the PS-ON Transistor to be ON all the time.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

And what drives it is the MT8202, right? That's what made me come to the conclusion that the BGA chip is bad. Is that wrong?

Also, I'd like to jump back to this Q21 for a second if you don't mind. That 5VSB, that's normally 5V, right? So, when Q21 is on, that 5V goes to gnd through the transistor but when it's off, that 5V travels down pin 6 of J23 to provide HIGH for PS_ON? Is that right?

[budm]

Re: Anyone familiar with the Akai LCD3701AD?

Also, I'd like to jump back to this Q21 for a second if you don't mind. That 5VSB, that's normally 5V, right? So, when Q21 is on, that 5V goes to gnd through the transistor but when it's off, that 5V travels down pin 6 of J23 to provide HIGH for PS_ON? Is that right?[/QUOTE]

5VSB = 5V Standby Power supply which is present the minute the power cord is plugged into an AC outlet.
Q21 Collector has the resistor R339 (10K), think of Q21 as a simple switch, when Q21 is ON (switch is Closed) the current that flow through R339 will go to GND, Collector Voltage will be close to ground.
When Q21 is OFF (switch is open), then the current will flow through R339 out to pin 6 of the connector to turn on the Transistor (this Transistor is used to run on the OPTO) on the power supply board.

I did not at the SCH to see exactly where the BASE of Q21 goes to.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

Also, I'd like to jump back to this Q21 for a second if you don't mind. That 5VSB, that's normally 5V, right? So, when Q21 is on, that 5V goes to gnd through the transistor but when it's off, that 5V travels down pin 6 of J23 to provide HIGH for PS_ON? Is that right?

5VSB = 5V Standby Power supply which is present the minute the power cord is plugged into an AC outlet.
Q21 Collector has the resistor R339 (10K), think of Q21 as a simple switch, when Q21 is ON (switch is Closed) the current that flow through R339 will go to GND, Collector Voltage will be close to ground.
...

This is what I'm having a hard time understanding. Looking at the schematic, the 5V Standby Power supply that is always present the minute the power cord is plugged into the AC outlet....I don't get why it doesn't go down pin 6, regardless of the state of the transistor. My high school electronics teacher told us electricity always follows the shortest route. Looking at the schematics, it's a further distance to Q21 than it is to pin 6...this is what confuses me. If it wasn't for that, I'd understand the transistor here. Wouldn't the transistor need to be before J6? Like in between J6 and the 5V supply?

I did not at the SCH to see exactly where the BASE of Q21 goes to.

I looked at the NETLIST name and then I searched the PDF for 8202UP3_1.

Page 19 in Adobe shows the MT8202. Somewheres to the right, in that mess of text, I see 8202UP3_1 << 8202UP3_1 1

I think that one is coordinates. Maybe what ball it is on the MT8202? That was my guess.

[budm]

Re: Anyone familiar with the Akai LCD3701AD?

The standby power supply is used to run the processor MT8202 (the processor has to be alive to be ready to accept the command from the power switch or from the remote IR) that drive the base of Q21, so that is why Q21 is on.

"My high school electronics teacher told us electricity always follows the shortest route."
Well, think about this, lets say you have two resistors connected in parallel to 10V power supply, one resistor is 10 Ohms and another resistor is 10K Ohms, so based on that theory, then you think there will be no current flow through the 10K since 10 Ohms resistor has the least resistance.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

What's the OPTO? I googled it and tried searching but everything things I mean optocoupler. That appears to be a device that seems to transfer electrical signals between two isolated circuits by using light. I'm sure that's not what you was referring to.

[budm]

Re: Anyone familiar with the Akai LCD3701AD?

This is what I'm having a hard time understanding. Looking at the schematic, the 5V Standby Power supply that is always present the minute the power cord is plugged into the AC outlet....I don't get why it doesn't go down pin 6, regardless of the state of the transistor.This is what I'm having a hard time understanding. Looking at the schematic, the 5V Standby Power supply that is always present the minute the power cord is plugged into the AC outlet....I don't get why it doesn't go down pin 6, regardless of the state of the transistor.

If the Q21 is on (switch u=is closed) then the Voltage between the Collector and Emitter (connected to GND) will be very low depend on Vsat rating of the Transistor usually around 0.2~0.6V, so that means the Voltage on pin 6 will be around 0.2~.6V range.

[budm]

Re: Anyone familiar with the Akai LCD3701AD?

What's the OPTO? I googled it and tried searching but everything things I mean optocoupler. That appears to be a device that seems to transfer electrical signals between two isolated circuits by using light. I'm sure that's not what you was referring to.

OPTO = OptoCouple, yes that is what I am referring to. It is used in the power supply PS-ON circuit to isolate the PS-ON signal which is on the cold side of the circuit from the SMPS circuit which is in the HOT side of the power supply.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

The standby power supply is used to run the processor MT8202 (the processor has to be alive to be ready to accept the command from the power switch or from the remote IR) that drive the base of Q21, so that is why Q21 is on.

"My high school electronics teacher told us electricity always follows the shortest route."
Well, think about this, lets say you have two resistors connected in parallel to 10V power supply, one resistor is 10 Ohms and another resistor is 10K Ohms, so based on that theory, then you think there will be no current flow through the 10K since 10 Ohms resistor has the least resistance.

Yes, based on the information he said, there wouldn't be. But I know that's not true. So this is what confuses me. Is it just that he wasn't qualified to teach the course and provided incorrect information?

When Q21 is ON, why does the 5V flow just to GND and not pin 6? To me, the way it's currently drawn, it looks like a parallel circuit.

I remember learning (not too long ago, mind you) that the
voltage in a parallel circuit is the same across each component. I remember how to calculate the total resistance of a parallel circuit, 1/Rt = 1/R1 + 1/R2 + ...

So, with the 10K and 10 Ohm resistor, the total resistance would be around 10 ohms, right? Here's my math:

1 / Rt = 1/10000 + 1 / 10
1 / Rt = 0.0001 + 0.1
1 / Rt = 0.1001
roughly 10 ohms

**EDIT: I think I finally get it, read the next post to see if I'm right.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

This is what I'm having a hard time understanding. Looking at the schematic, the 5V Standby Power supply that is always present the minute the power cord is plugged into the AC outlet....I don't get why it doesn't go down pin 6, regardless of the state of the transistor.This is what I'm having a hard time understanding. Looking at the schematic, the 5V Standby Power supply that is always present the minute the power cord is plugged into the AC outlet....I don't get why it doesn't go down pin 6, regardless of the state of the transistor.

If the Q21 is on (switch u=is closed) then the Voltage between the Collector and Emitter (connected to GND) will be very low depend on Vsat rating of the Transistor usually around 0.2~0.6V, so that means the Voltage on pin 6 will be around 0.2~.6V range.

Ohhh! I think I finally get it!!!! It's very low because it's going to GND, right? The transistor works like a resistor a bit and dissipates the voltage, right?

[budm]

Re: Anyone familiar with the Akai LCD3701AD?

Ohhh! I think I finally get it!!!! It's very low because it's going to GND, right? The transistor works like a resistor a bit and dissipates the voltage, right?

In this case it is used as a switch, that why you should look as a switch being open or close except it has Vdrops (Collector-Emitter) on the switch.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

In this case it is used as a switch, that why you should look as a switch being open or close except it has Vdrops (Collector-Emitter) on the switch.

Gotcha! That makes a lot of sense. It took me a long time to figure out these little buggers (transistors). I have always tried figuring out how to use them as a switch but every time, I've failed. I've never been able to connect all the pieces. I think I finally understand!!! To make sure though, when I find some time, I'm going to make a simple circuit that uses a transistor to turn an LED on and off. I'll create it myself and use something like a PIC to drive it, although I could use just a push button switch or the PIC to drive the LED itself.

Also, do you think I'm correct about the MT8202 being faulty? If so, can you help me try to find two replacement MT8202's? I think this one is an MT8202E. I could only find a pack of five for 50$. I couldn't find a datasheet either for it, I wanted the temperature profile for my BGA rework station. I'll practice replacing BGA components on an old desktop PC to get the hang of things. I believe I have the MT8202E stencil.

Thanks Budm!

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

In this case it is used as a switch, that why you should look as a switch being open or close except it has Vdrops (Collector-Emitter) on the switch.

I shouldn't have said resistor. I just meant that 5V, minus whatever the resistor uses, the transistor has to bear the load before it hits ground, right? You know, there's a voltage drop across the transistor. Otherwise, if we hook 5V directly to GND, we'll get a short and things will get really hot. That transistor, when the voltage flows through it to GND, it uses up whatever voltage is left after it goes through the resistor. Because voltage always has to be 0 when it gets back to GND, right?