Akai LCT2662 with bad caps

[Toasty]

Re: Akai LCT2662 with bad caps

I found a very similar schematic for your set. I don't think it's 100%, but it appears to be close enough to get a good understanding. It's a large PDF file. ARRRRGH!!!

Did you clean up the mess on the board from the vented caps? That electrolyte is conductive and could be causing the problem.

It could be a problem on the back light inverter board. Do you get any illumination?

I don't see any 24v reading in your voltage readings? That's provided through connectors CN5 & CN8 that are side by side in the corner with big caps. They use 1/2 the connectors for (+) and the other for (-). The end towards the mounting hole is (-). Confirm the voltage.

One of those connectors supplies power to the inverter board. Disconnect the one that does and then power on the set and see if the noise goes away. It may not power on without it connected. I am not sure either way.

If it does power up and the noise goes away, then the likely suspect is the back light inverter board. They run about $60-70.

http://www.shopjimmy.com/back-light-...-lct2662-2.htm

If it does not, then pull the other connector and try again. If the noise remains, then I think the problem is still on the PSU. Try to localize the noise if you can. A paper towel tube to your ear may help.

If no 24v, check diode D10 & MOSFET Q2. They're on the 2 heat sinks adjacent to the big cap area. Also, check those power resistors for open. The (5) large gray ones mounted vertically and sleeved.

Toast

EDIT: Verify the new caps were installed correctly. Polarity-wise that is.

[PCBONEZ]

Re: Akai LCT2662 with bad caps

Behavior of the LCT2785TA.

From Main Power Switch OFF to ON -
- Light should go red and stay lit.

Press Standby button -
- Light turns green instantly and in 3-5 second the screen lights up with the "Akai" splash screen for a second and then immediately goes to the tuner's last selection without any interaction.

From ON when you press standby the screen goes dark immediately but the light doesn't turn red again for 3-5 seconds.

~
Hope that helps in some way.
.

[aliasdck]

Re: Akai LCT2662 with bad caps

Thanks guys, thats very helpful.

I'm a bit embarrased to say the noise I was hearing in the power supply after turning on the main power is simply the power supply energizing. I opened up my 42" Plasma for comparison and it sounds exactly the same when energized. I was just a bit suprised by how loud it sounded in this akai being the first time I had ever heard the noise from such a close proximity.

Further testing has shown the power supply is now in good working condition post recap. Toasty, the 24V supply is operating normally.

I found the service manual here:



I found the blon on (logic high or low) and blacklight signal (fed with a pwm signal - for backlight intensity) from the main pcb (out through cn2). I disconnected cn2 and manually connected 12V for the pwm and 5V for the blon on directly into the inverter board. I turned on the TV, and sure enough, the backlights were on.

So now I'm pretty much left assuming the main pcb is AFU.

There are a dozen or so small ksd caps on the main pcb. None of them are bulging or anything, but considering the failure rate of the ksd caps on the power supply (80%) I figure it can't hurt to try recapping the main pcb and see what happens.

[PCBONEZ]

Re: Akai LCT2662 with bad caps

The main PCB on mine had a slew of 5mm 85c caps on it.
Since I had it out anyway to replace some 6mm-12mm caps, I replaced the 85c 5mm down to 100uF too.
.

[hoadle]

Re: Akai LCT2662 with bad caps

I had Akai lcd3201td tv did same like you TV
Check volt at power supply is ok like service manual
find 2 1000uF/16V cap bad at main board replace still same problem
Please let me know when you done replace all cap at mainboard or find some thing wrong
Can't find the replace
HY634-27PCBL-DST / Ver 1.2 Pn# 0510A / LCDTV32 05-387/1021A on the mainboard
Akai MAIN PCB ASSY parts# 771EL32AD02-01 find on the some website but is out stock
Thanks

[crossfire454]

Re: Akai LCT2662 with bad caps

I have an AKAI LCT2662 that had the power supply replaced 16 months ago. Today the set powers up, the light changes from red to green, AKAI logo comes on and goes off and no picture. Sound works, channels change...just no picture.
What do I look for?

[PCBONEZ]

Re: Akai LCT2662 with bad caps

Replacement power supplies usually just get you a fresh set of crap caps.
It's better to rebuild them.
.

[PlainBill]

Re: Akai LCT2662 with bad caps

I have an AKAI LCT2662 that had the power supply replaced 16 months ago. Today the set powers up, the light changes from red to green, AKAI logo comes on and goes off and no picture. Sound works, channels change...just no picture.
What do I look for?

PCBONEZ implied the obvious one - look at the caps in the power supply. The first thing to check for is the backlights - do they go off when the logo goes off? (Doing this in a dark room will help - the backlights should be obvious.) Check if you can see a picture on the screen if you shine a very bright flashlight on the screen.

IF the problem is the backlights go off, the next thing is the caps, followed by checking the backlight control line (sometimes labeled as BL_ON).

And it almost goes without saying, a clear, well lit picture of the back of the TV (with the back removed) will help us help you. Attach it using 'Manage Attachments;' - below the text entry area.

PlainBill

[crossfire454]

Re: Akai LCT2662 with bad caps

Many thanks. I was able to determine the gentleman who "replaced" my power supply simply replaced the caps in the original and charged me for a new power supply and install. I got a list of the caps needed plus another power supply on order. I'll install the replacement and repair the original..again.
Again, many thanks.

[DakotaKid]

Re: Akai LCT2662 with bad caps

I don't know if the preference is to use this thread or start a new one but the topic is the same so I will start here. Picked up one of these today, original owner told me symptoms and it sounded like PS caps to me. Man, this TV is a heavy bugger. Got home, pulled the back off, removed the cage on the PS and wow! I have never seen a mess like that on a PS before. Almost every cap was blown, around 20 in all, and there was electrolyte all over the board. One cap had literally blown its side out and spilled everything it had inside. The cap counts have been mentioned so I won't repeat them. I desoldered all of the caps and ordered replacements tonight. I have never seen an LCD with so many caps and every one was a crap cap. It was the biggest single cap disaster I've ever witnessed, it looked the Exxon Valdez had been there.

While I wait for the caps to arrive, I plan to clean up the mess on the board. What is the best way to soften up and remove the hardened gunk on the surface of the board? Is the dried up electrolyte still conductive? Guess I will have to run a continuity check on the gunk.

btw, not only do they use more caps and the worst caps available but they are also very unconventional voltages from what I've come across in the past. The 3300's are 35V and the 2200's are 25V. This number and cost of these fellas makes this a relatively expensive repair at just over $30 for all of the caps. Most of the power supplies I've done have been under $10. I had to stop and ask myself if it was worth repairing. Well, of course it is, I just hope this is the extent of the damage.

Thanks in advance for any advice on board cleanup and I will keep everyone abreast of my progress.

DK

[cmj21973]

Re: Akai LCT2662 with bad caps

When I did mine, I use 91% rubbing alcohol to soften it and a x-acto knife to scape it off.

If there is any areas of missing conformal, you can use brush on laquer to repair it.
https://www.badcaps.net/forum/showpo...6&postcount=10

[DakotaKid]

Re: Akai LCT2662 with bad caps

Received my caps in the mail yesterday, replaced them and it works like a champ, good as new, $30 total out of pocket. A few of the caps were a tight fit since the 3300uf were a bit larger diamter than the crapcaps I took out. Also, the 2200uf were a bit longer than the originals and smaller diameter so that was a positive. This board is horribly engineered with components so close together and on top of jumpers that there is great potential for shorts and/or unwanted contact. I am wondering if the case on the exploded capacitor might have been energized because of how close it is to a leg of a resistor that mounts near it. Good luck to others.

[crossfire454]

Re: Akai LCT2662 with bad caps

Ok, caps aren't the fix. While a TV guy here is telling me that the picture tube is probably bad, I am also being told that it's the bulbs and that checking them one at a time is the way to go. I have no idea how to do that, but I'm sure someone knows. I have a replacement inverter board on hand. So where do I get replacement lamps? (I'm in Dallas, TX.)

[deguello2003]

Re: Akai LCT2662 with bad caps

I just replaced the 3 main 1000 caps in the center of the board between the to retifer bridges all three were popped. After replacement and time for them to chargeup. Red ready light goes to green with the standby switch pushed and the unit began working as expected. I chose to replace the bad ones first and try it out befor wasting a lot of time replacing the ones that looked ok. We will replace them all now just for good measure. I recommend bench checking unit before it is reassembled just to save time but do not touch any of the high voltage parts of the board. Remember the caps will hold a charge for some time after unit is unplugged. BR