Proscan 42la 45h low power supply voltage and no sound

[pro_leonk]

Proscan 42la 45h low power supply voltage and no sound

Greetings all,
I picked up a 42" Proscan 42la 45h that was reported not to have sound. Upon inspection, it powered on and was buzzing really loud, video is good. I fixed the buzzing - it was the big 450v 150uf capacitor that was bad. Now I am able to hear some sound, but it is very faint on max volume and it is crackling. I did replace some capacitors on the power supply since I had them, but none of them did look bad(Replacements have line trough them diagonally). No improvements though.

The power supply board is: (HLP-45A01 or RSAG7.820.968/ROH ver. H
The main board is: E/RSAG7.820.997A Ver. D

Troubleshooting done:
With TV on, I get 24v as expected on the top right. I believe these are for video/ inverters. Half way down on the right side, i get good 12v, 5v, but where I am supposed to get 28v I only get 15.72v. I am a bit unsure about the 28v, as I thought there are only 5v, 12v, and 24v generally in TVs. The 28v is printed on the power supply board...

There is no other obvious damage on the board or components
See attached pictures.

Glad to take more pictures in more detail or do troubleshooting steps.

Thanks

[mmartell]

Re: Proscan 42la 45h low power supply voltage and no sound

Does the 28v go to the mainboard ? If so it will explain why your audio is acting up.

You may have more capacitors to replace yet.

[pro_leonk]

Re: Proscan 42la 45h low power supply voltage and no sound

Does the 28v go to the mainboard ? If so it will explain why your audio is acting up.

You may have more capacitors to replace yet.

Yes, it does go to the main board.
I am reading up more on the troubleshooting guides - could it be a voltage regulator that is acting up?

[leggot]

Re: Proscan 42la 45h low power supply voltage and no sound

It very well could be a voltage regulator, check all the voltages as they are likely culprits.

[freakaftr8]

Re: Proscan 42la 45h low power supply voltage and no sound

Replace capacitor C809. 390mfd. Trust me.

[pro_leonk]

Re: Proscan 42la 45h low power supply voltage and no sound

Replace capacitor C809. 390mfd. Trust me.

This one already got replaced, it was the first one. It had obvious damage and was leaking.
Going to go over the voltage regulators one by one.

[CapLeaker]

Re: Proscan 42la 45h low power supply voltage and no sound

Disconnect the 28V on the main board and turn the power supply back on. Force it on, if you have to and check if the 28V are back. Maybe something is dragging the 28v line down on the main board.

[pro_leonk]

Re: Proscan 42la 45h low power supply voltage and no sound

Disconnect the 28V on the main board and turn the power supply back on. Force it on, if you have to and check if the 28V are back. Maybe something is dragging the 28v line down on the main board.

I did that and I get a minor improvement, now I get 16.96v instead of the 15.72v.

[budm]

Re: Proscan 42la 45h low power supply voltage and no sound

Can I see good clear picture of the bottom side of the that clearly show the traces?
As shown on the board, the label shows it has 28V output at 1A or 14V at 1.5A this output is not regulated, that is lots of power. I wonder if it is used for the Audio power amplifier circuits.
You should check the current draw on this output.

[pro_leonk]

Re: Proscan 42la 45h low power supply voltage and no sound

Did some measuring on the voltage regulators (all on the cold side)
See bottom for more info


The next two are on the right side.
Center.
2576t-adj
RVA744 G
PIN 1 23.92v
PIN 2 12.13v
PIN 3 0v
PIN 4 1.19v
PIN 5 0v

Top
SP744
U1620G
AKA
PIN 1 0v
PIN 2 24.1v
PIN 3 0v

These are on the left side of the heatsink
Top
SP744
U1620G
AKA
PIN 1 0v
PIN 2 23.98v
PIN 3 0v


Center
SP744
U1620G
AKA
PIN 1 0v
PIN 2 16.96v
PIN 3 0v

Bottom
SRF1560
I will have to look up how to test that in more detail, appears to be a diode/ SCHOTTKY BARRIER RECTIFIER


The center left one seems to be very close to the voltage of the one where I am supposed to get 28v. This was the voltage with the main board (just where the 28v is plugged in is) disconnected. With it connected I got15.9v on the center pin. Appears that I narrowed down the issue a bit further.
At this point should I order a replacement part, or will I go down further the circuit and do more testing - like the resistors next to it, given that they are on the same circuit.

Cheers

[pro_leonk]

Re: Proscan 42la 45h low power supply voltage and no sound

Can I see good clear picture of the bottom side of the that clearly show the traces?
As shown on the board, the label shows it has 28V output at 1A or 14V at 1.5A this output is not regulated, that is lots of power. I wonder if it is used for the Audio power amplifier circuits.
You should check the current draw on this output.

Here is the board for now. I will check the current draw tomorrow.

[budm]

Re: Proscan 42la 45h low power supply voltage and no sound

Thanks for the bottom view picture but I cannot tell which pins are which, I cannot see the pin labels on the top side of the board due to the cables are in the way. I am trying to see which winding of the transformer generates the 28V.

[CapLeaker]

Re: Proscan 42la 45h low power supply voltage and no sound

What part number is N811? Just to clarify to make sure it is the one that is supposed to make the 28V.
I think it is a MURF1620 ultra fast recovery diode. Did you take it out and check it with your diode tester?
both diodes (pin 1 and 3) should read the same (to common pin2).
Those are a pretty common rectifier

[CapLeaker]

Re: Proscan 42la 45h low power supply voltage and no sound

Thanks for the bottom view picture but I cannot tell which pins are which, I cannot see the pin labels on the top side of the board due to the cables are in the way. I am trying to see which winding of the transformer generates the 28V.

Back side of the board pic, right under the middle board mounting hole, the first 2 pins from top to bottom are the 28V, next two pins are GND.

[pro_leonk]

Re: Proscan 42la 45h low power supply voltage and no sound

Thanks for the bottom view picture but I cannot tell which pins are which, I cannot see the pin labels on the top side of the board due to the cables are in the way. I am trying to see which winding of the transformer generates the 28V.

They are L807 (the larger top one) and L810 (the smaller bottom one)

[pro_leonk]

Re: Proscan 42la 45h low power supply voltage and no sound

What part number is N811? Just to clarify to make sure it is the one that is supposed to make the 28V.
I think it is a MURF1620 ultra fast recovery diode. Did you take it out and check it with your diode tester?
both diodes (pin 1 and 3) should read the same (to common pin2).
Those are a pretty common rectifier

Hi, it is the 2576t-adj RVA744 G. Voltage readings are in the previous post. The
MURF1620 is VD812. I still have to test it out of circuit.

[CapLeaker]

Re: Proscan 42la 45h low power supply voltage and no sound

uff... where did I get the MURF1620 from being in N811 spot? Dang... must have been asleep or something got cross-eyed ... lol

[pro_leonk]

Re: Proscan 42la 45h low power supply voltage and no sound

Problem solved. I managed to fry something on the main board (the volume amplifier while testing there). Got a replacement board from eBay and the sound is back.
Appears that the power supply was good, even tough the voltage seemed lower...

Thanks for all your help. I learned a few things for future troubleshooting.

[johnboy1313]

Re: Proscan 42la 45h low power supply voltage and no sound

it powered on and was buzzing really loud, video is good. I fixed the buzzing - it was the big 450v 150uf capacitor that was bad

Are you sure it wasn't a 250V 390uf cap? I just fixed the same set with the same power supply. Mine had a 259V 390uf big cap. Your picture definitely has a 390uf cap. I can't tell the voltage. I swapped that cap and the buzzing ceased.

[pro_leonk]

Re: Proscan 42la 45h low power supply voltage and no sound

I did replace that cap because it was buzzing pretty loud, but it did not improve the sound issue that I had.
I just looked at the pictures I posted, and yes, it is indeed a 250v 390uf (it was already replaced at the time of the picture) so I must have mixed it up with a other cap.