Amplifier snaps, crackles, & pops for first 3 minutes, then works fine

[smalltownguy]

I've got an Olivia 42" LCD TV (542-B11) with an onboard amplifier that snaps, crackles & pops pretty bad when you first turn it on. Doesn't matter if the volume is high, low, muted, or speakers turned off in menu, the sounds continue to crackle (at the same loudness) for about 3 minutes, and then slowly dissipates to normal operation. Turning off the TV for 60 seconds or less prevents the problem from reappearing, but turning it off for any length of time (more than 5 minutes) will cause it to happen again. All other functions of the TV are fine. I suspect bad caps in the audio amp. Anyone else have any other ideas? I don't think it's a transformer issue because the sound works just fine once the TV has 'warmed up' so to speak.

[kaboom]

Re: Amplifier snaps, crackles, & pops for first 3 minutes, then works fine

Bad connections/solder in the power amp. This would be after the volume control ICs, which is all the menu adjustments would affect.

As it heats up, the board and parts expand and connections 'get better.'

Good luck, you may have one of those PWM switching amplifiers. Hopefully, you don't have to deal with any of the SMTs.

-Paul

[smalltownguy]

Re: Amplifier snaps, crackles, & pops for first 3 minutes, then works fine

Where should I be looking for the power amp? I've got basically 3 pcb's on this TV - the power supply, the tuner card pcb, and the main pcb.

I used a hose to try and zero in on the crackling at board level and it's coming from the area near where the speaker inputs plug in to the pcb. There's a row of 4 inductors near the speaker outputs, and it sounds like they're sizzling pretty good at startup. It's really hard to tell if it's those 4 inductors or the capacitors nearby.

As far as the power amp goes, wouldn't I see some large transistor mounted on a heatsink somewhere for the sound amp?

[kaboom]

Re: Amplifier snaps, crackles, & pops for first 3 minutes, then works fine

There's a row of 4 inductors near the speaker outputs

As far as the power amp goes, wouldn't I see some large transistor mounted on a heatsink somewhere for the sound amp?

You've got a PWM amp- there should be an IC that feeds those inductors, which then feed the speaker outputs. Those inductors are part of the LC output filter. This is to an amplifier what a switching power supply is to an 'old-fashioned' linear supply. As you've found out, it looks nothing like a conventional amplifier.

Try poking the board with a wooden dowel when it seems to be acting up. This assumes you can run it opened up without disconnecting anything. There are usually plenty of SMTs in one of these, so don't knock any loose.

-Paul

[smalltownguy]

Re: Amplifier snaps, crackles, & pops for first 3 minutes, then works fine

I found a pretty decent price on a full main board, so I replaced it. Problem solved.

[Uranium-235]

Re: Amplifier snaps, crackles, & pops for first 3 minutes, then works fine

snap crackle pop? maybe you accidentally got some rice crispies inside it

[smalltownguy]

Re: Amplifier snaps, crackles, & pops for first 3 minutes, then works fine

snap crackle pop? maybe you accidentally got some rice crispies inside it

*rimshot*

Anywho...I ended up replacing the main board on this TV for $80. Owner was happy, and he got a spare board to keep should his new one crap out (albeit that old board cannot use audio).

I probably could have swapped capacitors or inductors on this, but since they were so very small I feared I would have damaged the board in the process.