LG T250SC DVD receiver - noise from the speakers

[televizora]

Well, hello again, dear friends.
Today I will torture you with my problems again.
I have a problem with my old DVD receiver, that I used to use as audio system some time ago. I have only a noise from the speakers - all of them. It doesn't matter if you turn the volume to the minimum or blast it to the max - the noise doesn't change at all as intensity
I've checked the PSU voltages and I've found that 35V a lit a little bit low - about 27V. Everything else checks as it should.
The receiver uses a pwm driver and BA505, so perhaps it's hard to diagnose without a proper equipment..
I would be extremely glad if you can help me with this problem.

[budm]

Re: LG T250SC DVD receiver - noise from the speakers

What is the full model number?
https://elektrotanya.com/showresult?...oria=&kat2=all

[televizora]

Re: LG T250SC DVD receiver - noise from the speakers

What is the full model number?
https://elektrotanya.com/showresult?...oria=&kat2=all

LH-T250SC P/N 3850RLM008F
2xSTA 515 as a final stage amplifiers.
BA5954FM as a actuator driver
Pulsus ps9818 as a digital sound processor/PWM driver of the STA515

[Andrew F. Ali]

Re: LG T250SC DVD receiver - noise from the speakers

27V is a bit low. Re-test/replace all the smaller e-caps on the PSU. Investigate why that voltage is so low. The large filter e-caps should be good, though

[televizora]

Re: LG T250SC DVD receiver - noise from the speakers

27V is a bit low. Re-test/replace all the smaller e-caps on the PSU. Investigate why that voltage is so low. The large filter e-caps should be good, though

Well...I think..If one of the STA-s is shorted, do you think that it's possible for the voltage to drop that low? I cant separately test the STA-s, because they are not usual final stage amps and I can't just supply the inputs with some signal.
So, I have noise from the speakers. When I move the board or connect antenna, then I can hear cracking for a second from the speakers. I cant regulate the volume neither from the front panel, nor from the remote.
The problem is that there are 2 STA-s, and I hear only noise from all the speakers. This means that either both are busted, there is a problem with the driver or there is other issue that affects both the STA-s.
Do you think that this can be power supply issue?

[televizora]

Re: LG T250SC DVD receiver - noise from the speakers

WTF!!?Yesterday, I heard a strange noise, but thought that it comes from the PSU. Today I've tested the receiver again. I've connected antenna to the FM antenna jack. When I increase the volume to the maximum, I can hear a faint sound from the radio station that is being received coming from the FM tuner itself!!? Something inside the tuner is oscillating as well as both the STA-s are warming up the coller placed on top of them.
Please help!?

[televizora]

Re: LG T250SC DVD receiver - noise from the speakers

It's one of the STA-s. I've cut the power of the one of STA-s. Before, there was some sound from the front left channel. From all the other channels - only noise. Now I have 3 channels that work and there isn't any noise.
What I did is to cut the trace with +36V to the STA that is responsible for the sound on the front right, SubWoofer and back right. Kinda ghetto mod. Now I will look for another STA, perhaps I will order one. They are cheap - something like 5$. I didn't think that one defective STA will interfere with the sound coming from the other STA, as they are separate IC-s. Seems like the noise passes tru the common ground the the two STA-s.