Akai 27" Turns on and off and on and....

[capxrf]

I'm back with another issue on another tv:

This is a strange problem to me. Maybe someone else has experienced it as well.

I received a 27" Akai tv with built in dvd player Model Number LCT2701TD.

When I plug the unit in and flip on the main power switch (not the "ON" button), the tv automatically kicks on and the screen comes up for about 2-5 seconds, then it kicks off, then it repeats. Pressing the power on button does nothing to the cycle. I assumed power supply, or stuck button.

The tv does the same thing whether or not the control buttons are connected or not, so that's out. As for the power supply, there are no signs of damage. (no bulged capacitors, no burn marks, no loose components, etc).

I'm stuck as to why this would happen anyway. On the back of the power supply, there is an IC that has a jumper wire soldered on (the IC appears to be labeled 4407P 355D9 and I have read other reports of people finding this same repair on the identical model, so it must have been on purpose by factory or such)

Any thoughts?

[kc8adu]

Re: Akai 27" Turns on and off and on and....

lots of small lytics baked dry under the heatsinks on those megmeet psu's.replace all the lytics anyway.
i have a 37" here that would just randomly restart.+5 was going low and high intermittantly.a recap fixed it.
these units run too hot.

[capxrf]

Re: Akai 27" Turns on and off and on and....

Alright, I'll give it a shot. They just all look good. It's gonna be a chore getting the few that are under the heatsinks.

[capxrf]

Re: Akai 27" Turns on and off and on and....

Ok, I re capped the power supply board, and nada. No change at all. What could possibly be making it turn on by itself when plugged in and then power cycling over and over? I'm at a complete loss. Anyone had similar?

[aliasdck]

Re: Akai 27" Turns on and off and on and....

I can't get a good enough look at the picture of the power supply to be able to offer any specific pointers, but I would suggest you probe the power supply voltages while the TV is turning on and off. Try to see if the voltages are stable and accurate while they are on.

Another thing to check may be the control voltage feed into the power supply (usually from logic board or mainboard... my terminology may not be accurate here). This may be a 3.3v or similar voltage that turns on the power supply and puts it into standbye when not present (or something similar). This pin may be labelled something like "remote" "on/off" or the like.

By measuring this voltage and paying attention to the what the TV is doing, you may be able to determine if the power supply is being commanded to turn off by an external logic signal or if the power supply is shutting itself down...

Another thing, I believe this TV uses a darfon inverter board which (some models) are known for developing open secondaries in the inverter transformers. I'm not sure which specific inverter this TV uses, but its a possibility. If there is an open transformer, then the TV would shut down the power supply after a couple seconds as you are seeing... but I'm not sure why the TV would continously cycle on and off as it is. But it may be worthwhile to atleast ohm out each transformer and see what you get.

[capxrf]

Re: Akai 27" Turns on and off and on and....

alright I finally had time to mess with this again. I don't believe this is a power supply issue anymore. I kinda did what aliasdck suggested except not all the outputs are labeled... so i instead did this:

I hooked the main board power-in connectors to an external power supply with the correct voltages (these ones I know). Nothing unnecessary is hooked up to the main board. Only power-in, and the tiny board that has the power on light (so i know if it's working or not. This results in the same actions. It keeps powering on then to standby (off) then to on and so on... It must be something on the main board. I'll work on getting a picture of the main board soon. Any ideas of what it may be that would make this happen?

[capxrf]

Re: Akai 27" Turns on and off and on and....

This is the main board I am talking about.

[RicB]

Re: Akai 27" Turns on and off and on and....

When we used toget tube tv's into our shop with the same problem it was bad solder most of the time...solder heats up expands breaks connection...cools down contracts makes connection...do you hear the coil click when the tv goes off?

[capxrf]

Re: Akai 27" Turns on and off and on and....

yes. That too, I can hear the power supply click on and off, but of course, not when the external power supply was used. (I had it hooked up to an old computer power supply)

[stj]

Re: Akai 27" Turns on and off and on and....

maybe the tubes are drawing too much current.

[kc8adu]

Re: Akai 27" Turns on and off and on and....

maybe the tubes are drawing too much current.

one could always disconnect the inverter and see if it stays on.
this could even be a corrupted firmware issue.

[capxrf]

Re: Akai 27" Turns on and off and on and....

well, this is an LCD tv. No tubes. I have already tried disconnecting the inverter board and it made no difference

[capxrf]

Re: Akai 27" Turns on and off and on and....

How would i go about fixing a firmware issue? would anyone no how to reset this tv?

[stj]

Re: Akai 27" Turns on and off and on and....

time to get "old school",
try desoldering or isolating the audio-amplifier.

[capxrf]

Re: Akai 27" Turns on and off and on and....

the audio amp? Just curious, why do you jump to the audio? I have already tried turning on the unit with the "amp connector" (thats what it is labeled as) disconnected from the main board

[stj]

Re: Akai 27" Turns on and off and on and....

the description sounds like an overload-shutdown,
audio amplifiers can short-out & draw high levels of current.

but you already tried that - so it's not.
maybe defaulting the eeprom, but you'd need a service-manual or a lot of experimenting.

[PlainBill]

Re: Akai 27" Turns on and off and on and....

the audio amp? Just curious, why do you jump to the audio? I have already tried turning on the unit with the "amp connector" (thats what it is labeled as) disconnected from the main board

As a general rule, when a plasma, LCD, or other digital TV powers up it does a number of self tests, one of which often includes the current draw in the audio amp section. In one Philips set I studied extensively such a fault would send the set into 'protection status' where it would flash a led in a pattern indicating the error. The only way to exit protection status was to unplug the set until the standby power supply discharged - a couple of minutes.

Practices vary from manufacturer to manufacturer, and even from model to model, but it is not unlikely that a shorted power amp or even a bad speaker could cause the problem you describe. As stj suggests, find the service manual. Some are a waste of paper; others contain a great deal of troubleshooting information.

PlainBill

[delaware74b]

Re: Akai 27" Turns on and off and on and....

Capxrf -I'm working on the same model tv except that it has many bulged caps on power supply board. The service manual is available online for free and it is very detailed (100 pages in pdf). I have a copy of it and PM me if you want a copy.

[mrosenberg42]

Re: Akai 27" Turns on and off and on and....

I fixed an LCD monitor with a similar issue. It ended up being a shorted transistor.

[hoadle]

Re: Akai 27" Turns on and off and on and....

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 (my main board look like main board on Akai LCT2701TD)
Please tell me what transistor you replace & where at main boar?
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
Here you service manual