Akai LCT37Z4AD Has very dim backlight

[TubeJunkie]

Hello. I have an Akai LCT37Z4AD TV that I picked up from the recycle center. When I powered it on, The power light goes from blue to green, but it had no backlight. I opened it up and found bulging caps on the Tuner/input board. I changed those bad caps, and powered it back on. Now I have a very faint backlight. I can faintly see the Akai logo when starting up. I know I need to check voltages on the power supply board next, which I will be doing ASAP. But I don't want to waste my time if I have bad backlight boards. Any advice will be greatly appreciated. Thanks!

[budm]

Re: Akai LCT37Z4AD Has very dim backlight

You should check the Dimming control signal Voltage to see what it is right now.

[TubeJunkie]

Re: Akai LCT37Z4AD Has very dim backlight

I've looked at the Service Manual and can't figure out the location to check the dimmer voltage supply. I've looked at the power supply board also, and can't locate it. I did check the voltages on the cable going from the power board to the Slave inverter board, and only the first red & white wires has voltage. That first red wire has 5.03vdc, and the white wire has 2.95vdc.

The master inverter board has the power supply board minted directly on top of it , so it's about impossible to check it's voltages. Thanks for your reply budm

[budm]

Re: Akai LCT37Z4AD Has very dim backlight

OK, this looks like one of those Polaroid/Westinghouse chassis, it does not have the BL-ON or the DIM control passing through the power supply board.
Can I see the picture of the whole backside of the TV?

[TubeJunkie]

Re: Akai LCT37Z4AD Has very dim backlight

Sure. It has the built in DVD player on the left. I have the service manual, but it's too big to upload. Web link to the SM below. You can download the entire manual once you get there. Thanks for taking the time for me. Much appreciated.

https://www.manualslib.com/manual/10...2.html?page=57

[budm]

Re: Akai LCT37Z4AD Has very dim backlight

I can see the inverter board under the metal shield, there may be pin lable on the inverter connector to tell you which one is the Dim control pin.

[TubeJunkie]

Re: Akai LCT37Z4AD Has very dim backlight

Here's a picture of that inverter board that's mounted under the power supply board. I didn't see anything marked dimmer or dim. I did notice the copper ground contacts (screw points) we're corroded, so I cleaned them. But didn't make a difference. This inverter board is smaller than the other one. So I'm guessing it's the Slave.

[budm]

Re: Akai LCT37Z4AD Has very dim backlight

Look like you need to look at the Master inverter board.
Can we see the pictures of the Master?
Is this the Master Inverter board you have?
http://www.shopjimmy.com/akai-pb-051...t-inverter.htm
If it is, then check the DC Voltage on TP7, TP8 and report what it has.

http://www.shopjimmy.com/catalogsear...Akai+LCT37Z4AD

[chrismurphy]

Re: Akai LCT37Z4AD Has very dim backlight

It looks like you have at least one as far as i can see on the power board under the metal shield
I have never seen bulging caps on tuner boards

[budm]

Re: Akai LCT37Z4AD Has very dim backlight

I've looked at the Service Manual and can't figure out the location to check the dimmer voltage supply. I've looked at the power supply board also, and can't locate it. I did check the voltages on the cable going from the power board to the Slave inverter board, and only the first red & white wires has voltage. That first red wire has 5.03vdc, and the white wire has 2.95vdc.

The master inverter board has the power supply board minted directly on top of it , so it's about impossible to check it's voltages. Thanks for your reply budm

BTW, you do have 24VDC to the inverter boards, correct?

[TubeJunkie]

Re: Akai LCT37Z4AD Has very dim backlight

Hi budm Here's the voltage checks and a pic of the master inverter board. And Yes, that's the same board on ShopJimmy. Is those voltage readings ok? Or does that tell us the master inverter board is the problem? Thanks again for your help.
TP7: 5.0 vdc
TP8: 3.0 vdc

[budm]

Re: Akai LCT37Z4AD Has very dim backlight

OK, they look OK.
TP7 looks to be for BL-ON
TP8 looks to be for DIMMING, at 3V the backlights should be quite bright. 5V = Max Brightness, 1V (typ.) = minimum dimming.
So you do have 24Vdc on both ends of the fuse with ref to GND on the MASTER and the SLAVE inverter?

[TubeJunkie]

Re: Akai LCT37Z4AD Has very dim backlight

I have no DC voltage on either end of the fuse of the master inverter board. But it has continuity when tested with power off and meter set to continuity. The only fuse I see on this board is a square ceramic type labeled 60v 6.3A. I can't test the Slave inverter board fuse voltage due to it being mounted under the power supply. But I could remove power supply and check for continuity. Thanks budm

[nomoresonys]

Re: Akai LCT37Z4AD Has very dim backlight

I have no DC voltage on either end of the fuse of the master inverter board. But it has continuity when tested with power off and meter set to continuity. The only fuse I see on this board is a square ceramic type labeled 60v 6.3A. I can't test the Slave inverter board fuse voltage due to it being mounted under the power supply. But I could remove power supply and check for continuity. Thanks budm

Sound like a good idea.

[TubeJunkie]

Re: Akai LCT37Z4AD Has very dim backlight

I checked the fuse on the Slave inverter board and it has continuity. Where should I go from here?

[nomoresonys]

Re: Akai LCT37Z4AD Has very dim backlight

I'm not sure but for 19.34 for that master inverter, I would buy that, if it isn't the problem it doesn't hurt to have a spare and it's an easy way to eliminate the inverter if the one you get is a good one, but if another problem is blowing things on the inverter then that would be bad.

[maxvalutech]

Re: Akai LCT37Z4AD Has very dim backlight

From the schematic pin8 is BLon, pin7 pwm, pins 1 2 3 v-in with gnds 4 5 6. A 2007 model so good learning project.

[budm]

Re: Akai LCT37Z4AD Has very dim backlight

So at this point you do not have 24VDC, 0VDC per you report on the Inverter fuses.
Checking Voltages on the power supply board will be next.
Can I get straight shot pictures of the whole bottom side of the power supply board?

Megmeet MLT586K may be close to your Megmeet MLT586A board.
http://www.shopjimmy.com/megmeet-mlt...er-supply.htm#

As you can see, there are pin labels on the bottom side of the board that we need to check.

You can also disconnect both 24VDC power cables going to both inverters to see if the 24Vdc out on the power supply will be present or not.

[TubeJunkie]

Re: Akai LCT37Z4AD Has very dim backlight

Here's the pic of the bottom/solder side of the power supply board. I reassembled it an took some voltage readings on the 24vdc pins that go to the inverter boards. I DO NOT have any DC voltage on any of those pins.

[nomoresonys]

Re: Akai LCT37Z4AD Has very dim backlight

So at this point you do not have 24VDC, 0VDC per you report on the Inverter fuses.
Checking Voltages on the power supply board will be next.
Can I get straight shot pictures of the whole bottom side of the power supply board?

Megmeet MLT586K may be close to your Megmeet MLT586A board.
http://www.shopjimmy.com/megmeet-mlt...er-supply.htm#

As you can see, there are pin labels on the bottom side of the board that we need to check.

You can also disconnect both 24VDC power cables going to both inverters to see if the 24Vdc out on the power supply will be present or not.

So is the 24VDC going to both inverters?