Anyone familiar with the Akai LCD3701AD?

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

I'm going to go pull some more MOSFETs and test them while I'm waiting for your guy's response.

The measurements where with the logic board (I call the "main" board a logic board) hooked up.

[budm]

Re: Anyone familiar with the Akai LCD3701AD?

You are not getting the PS-ON command from the main board that is why you are not getting the switched 5V, 8V, and 12V.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

You are not getting the PS-ON command from the main board that is why you are not getting the switched 5V, 8V, and 12V.

Oh, so it's not something with the power supply but something with the main board then, right? I should take the 1Kohm resistor and jump between the 5V_STBY and the PS_ON?

When I hit the on button though, would PS_ON stay high or would it just go high for a bit and then go low again?

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

Do I have to use a resistor or can I just take an alligator clip and jump 5V_STBY to PS_ON?

[budm]

Re: Anyone familiar with the Akai LCD3701AD?

Oh, so it's not something with the power supply but something with the main board then, right? I should take the 1Kohm resistor and jump between the 5V_STBY and the PS_ON?

When I hit the on button though, would PS_ON stay high or would it just go high for a bit and then go low again?

PS-ON is generated by the main board, most TVs use Active high, >2.5VDC = ON, <1VDC = OFF. The signal is the steady state.

Always use the resistor in case you make the wrong connection, the resistor will limit the current, and when doing the force on of the power supply board, you MUST disconnect the cable going back to the main board first.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

I was thinking of using my programmable power supply and just providing 3.0VDC. If I set the current real low, like .1 amps or something, would I still need the resistor? I'll use the resistor and just some jumper cables I'm making and jump it to the 5V_STBY. I just wanted to know for future use.

Why must I disconnect the cable going back to the main board first? I have an idea but I want to make sure I'm right. Is it because, like you said, the main board provides the voltage for the PS_ON, but when I'm providing the power to PS_ON myself, it'll go back to the logic board through the cable and damage the logic board?

[budm]

Re: Anyone familiar with the Akai LCD3701AD?

You can use external supply if you want, it requires very little current, just enough to Bias on a transistor.
You have to disconnect the cable abck to the main board because the transistor on the main board that supply the ACTIVE HIGH is normally, or stuck ON due to fault circuit, so if you jump the 5V to the PS-ON pin without disconnecting the cable back to the main board which the transistor is fully on (think of it as switch that at Ground) then you can burnt up that transistor because the 5V will be grounded through that transistor, that is why I always say to use resistor in case you forget to disconnect the cable first. And if you accidentally connect the 5V to the wrong pin such as ground then you can damage the 5V supply.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

You can use external supply if you want, it requires very little current, just enough to Bias on a transistor.
You have to disconnect the cable abck to the main board because the transistor on the main board that supply the ACTIVE HIGH is normally, or stuck ON due to fault circuit, so if you jump the 5V to the PS-ON pin without disconnecting the cable back to the main board which the transistor is fully on (think of it as switch that at Ground) then you can burnt up that transistor because the 5V will be grounded through that transistor, that is why I always say to use resistor in case you forget to disconnect the cable first. And if you accidentally connect the 5V to the wrong pin such as ground then you can damage the 5V supply.

Thank you Budm for the explanation.

We have Corning Appliance here doing a lot of work and I haven't had much time to work on the TV but I'm going back down now. I made my jumper wires using wires from an old computer. They were for the reset switch and LED. I just removed the header, then where the wire was connected to the LED and where the other wire was connected to the switch, I cut it, striped it and soldered a resistor in between them. Then I used some heat shrink tubing to protect it. The cables plug nicely into the pins on the power supply board. So, I'll hook my jumper up and then provide the 120VAC and take measurements.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

I'm such an idiot. I've been testing the wrong board this whole time. When I hooked my jumper up, all the voltages read as they were supposed to. The far right one in the pic that is supposed to read 24VDC reads around 22VDC, but I don't think that's any issues.

Do you think it could be that transistor on the main logic board that might be bad?

[budm]

Re: Anyone familiar with the Akai LCD3701AD?

You will have to get the schematic of the main board or you can try tracing the PS-ON pin to see where it goes to on the board.

[budm]

Re: Anyone familiar with the Akai LCD3701AD?

BTW, if you can force on the power supply with the PS-ON wire is disconnected but the connector is back in place so the main board will get the power to run the main board, if everything else is OK then you should have all other the functions of the TV and have sound and pictures on the screen, if not then you have more than just bad PS-ON signal.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

Here's pictures of those transistors. There's two of them on the board. Not sure which one is used for the PS_ON. Any suggestions on how I should test them?

They both appear to have s1A then a sideways 66. They're a bit hard to read in the two pictures.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

I didn't refresh the page before reading your post. I don't think I can remove just those pins and use my jumper. It'd be a bit hard to test. I can try, but there's a chance I might break the connector...

[vinceroger69]

Re: Anyone familiar with the Akai LCD3701AD?

Maybe just cut the ps-on wire for a test etc you could always resolder the ends and with a bit of heat shrink tube too make a nice safe repair.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

Maybe just cut the ps-on wire for a test etc you could always resolder the ends and with a bit of heat shrink tube too make a nice safe repair.

I'd also have to cut the 5V_STBY though. So the 5V_STBY wouldn't be hooked up...That wouldn't work right, would it? Unless I left the connector in there and did away with my jumper and then just pushed the cut PS_ON wire into the 5V_STBY wire...

But I'd still need the resistor, wouldn't I?

I thought I could take my DMM and just check the voltage going to the transistors to see if they were getting voltage when my wife hit the power button. If they were, I thought I could assume one was bad. Would that work or no?

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

I managed to safely remove the PS_ON wire from the header, without cutting it. I used an exacto knife to carefully pry the tab up on the header and just slide the wire out. Do I need to use the 1Kohm resistor still to jump the 5V_STB to the PS_ON? If not, I'm ready to go.

[budm]

Re: Anyone familiar with the Akai LCD3701AD?

You should use the resistor (470~1K will be fine) just in case.

[Spork Schivago]

Re: Anyone familiar with the Akai LCD3701AD?

Okay, I used the 1Kohm resistor and tried it. The red light blinks steadily and then all of a sudden, the backlight starts blinking steadily, with the red light. Nice and bright, on and off, on and off, on and off. Maybe a second or three apart.

[Spork Schivago]

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.

[ReeceyBurger123]

Re: Anyone familiar with the Akai LCD3701AD?

Just to add in Im familiar with that mainboard lol, I will let bud and you finish this though. Watch this:

https://m.youtube.com/watch?v=WojR82ocSck