Samsung HT-AS730ST

[Sam I Am]

I picked this unit up recently for practically free.
Powered it up and all it does is light up the power standby.
Checked the PS output voltages at the ribbon cables and the only voltage I'm reading is 5.6V @ Pin 11 of the CN3 connector.
I then checked the fuse and the bridge input/outputs. This is where I am confused as the bridge reads 110V AC on one leg while the other AC leg reads 17V. The output legs are reading 14V DC. Pulled the bridge and it checks fine.
I found the service manual for a nominal fee but I am totally stumped as to what is causing the bridge voltage readings to be what they are.
Man..... I feel like a total as the answer is probably staring me in the face but I'm not seeing it.

[momaka]

Re: Samsung HT-AS730ST

I then checked the fuse and the bridge input/outputs. This is where I am confused as the bridge reads 110V AC on one leg while the other AC leg reads 17V. The output legs are reading 14V DC. Pulled the bridge and it checks fine.

Are you measuring these values with respect to ground/case? If so, this is why you may be getting odd voltages. When measuring DC voltage on the primary (high-voltage) side of the power supply, always measure with respect to the hot ground - i.e. the negative side of the bridge rectifier.
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Now, you say your PSU is outputting 5.6v for standby. This means the primary side is good, or at least the standby circuit is, so don't mess with it yet.
Try measuring the voltages on CN2 and CN3 (with respect to ground/case) when you press the power button. Do any of them appear for a split second or pulse?

[Sam I Am]

Re: Samsung HT-AS730ST

me.
It was operator error. The bridge is reading 119V AC on the inside pins and 164V DC on the outside pins. That's more like it.
The 5.6V at Pin 11 CN3 is there regardless of the power button position.
I'm picking up right at +1V on Pins 4, 5, 6, 10, 11, and 12 CN2 with power button on.
All other Pin readings that are suppose to read +/- voltages (3.3, 5, & 12) are at 0V.
No fluctuations have been noted in voltage readings cycling the power button.

[momaka]

Re: Samsung HT-AS730ST

So all pins on CN3 are reading 0v except for 5.6v? Even P/ON?
First, check diode D32 (near CN3 connector). Is it good? If so measure voltage for P/ON both when power button is not pressed and when it is pressed and held down. Measure the voltage after it passes through D32 (i.e. on the cathode side of D32).
Anything?

P/ON is the high/low signal that triggers all the other voltage rails. The fact that 5.6v is present means P/ON should also go high (probably close to 5v) when the power button is pressed. So, either receiver's logic board is not working right and not sending the P/ON signal, or there's a fault in the PSU, pulling P/ON down and preventing the PSU from starting up.

If you get no voltage for P/ON, can you post a picture of the receiver's logic board (particularly, the one that connects to CN3).

[Sam I Am]

Re: Samsung HT-AS730ST

Okay.... I will start over and see if I can get it right this time.
I was cycling the power button to quickly as there is about a four second delay before any voltages start to register.
Learned something new today.
Starting with CN2 and power button on:
Pin 1 (+12V) = 12V then drops to 0V
Pin 3 (-12V) = - 12V then drops to 0V
Pins 4, 5, & 6 (+32V) = 32V then very slowly drops to 0V
Pins 10, 11, & 12 (-32V) = -32V then very slowly drops to 0V
Now on to CN3:
Pins 3 & 4 (+5V) = 5V then drops to 100mV
Pins 5 & 6 (+3.3V) = 3.2V then drops to 760mV
Pin 9 (P-S) = 5.5V
Pin 10 (P/ON) = 3.2V
Pin 11 (+5.6V) = 5.6V
Pin 13 (VFD+) = 32V then drops to 0V
Pin 14 (VFD-) = -33V then drops to 0V
Pin 15 (-VP) = -38V then drops to 0V
Hope this clears up some of my confusion.

[Sam I Am]

Re: Samsung HT-AS730ST

So.... since P/ON is low, what would be the most likely cause of this?

[momaka]

Re: Samsung HT-AS730ST

I was cycling the power button to quickly as there is about a four second delay before any voltages start to register.

Well, that's strange. How long did the voltages stay up before they dropped again? Does P/ON change at all when you press the power button? Also, do you get any voltage on the pin labeled P-S?

So.... since P/ON is low, what would be the most likely cause of this?

It might not be low. On some PSUs it's close to 5v, but I'm not sure if that's what it should be here or not.
Also, P/ON is a return signal *usually* generated by the logic board of the device and not the PSU itself. If you look at the schematic, you will see that P/ON points inward, not out, indicating an input signal going to the PSU.

Maybe post some pictures of the other boards as well. Perhaps someone else might be able to point out something I missed.

[Sam I Am]

Re: Samsung HT-AS730ST

I should of realized the four second delay thing as the Samsung LCD panels act more or less the same way when you power them up.
All of the voltages that drop off to 0V, "peak" for only a split second. "Peak" meaning the DVOM will show that particular rails correct voltage momentarily before dropping off to 0V or some other substantially lower value. If you are not looking directly at the meter, you will miss this "peak" reading.
P-S stays at 5.5V with power button on, goes to 140mV with power button off.
P/ON goes to 3.2V with power button on, then promptly drops to 30mV.
Pin 11 is at 5.6V regardless of power switch position.
I'm leaning toward a PSU issue of some type but then again