LG 60PA5500 No VSC or VY Voltage

[abbottdave]

I have a 60PA5500 with no VSC or VY voltage. Va is steady at 55V, Vs is a good 205V, and Vzb is a steady 120V. But I get nothing at VSC (should be 150V), and a fluctuating 7 to 24V at VY (should be -190). I've replaced the VSUS board with no success, and just recently replaced most of the semiconductors on the board - same result. I have good Va and Vs voltages going to the YSUS board, and the YSYS board hums (heat-sinks get barely warm), but no voltage at VSC or VY. Both fuses are good. Both upper and lower buffer boards have been replaced, with the same result. Any ideas?

[Andrew F. Ali]

Re: LG 60PA5500 No VSC or VY Voltage

1. Measure the M5V and see if it is remaining low...If it is then you have a Main Bd problem.
2. See if you are getting 15V from Y-SUS Bd to the X-PWB.
3. Check if you have 5V and 17V to the Control Bd.
4. Look for presence of 3.3V from Control Bd to the X-PWB.
5. VSC and -Vy voltages are generated in the Y-SUS Bd.

[abbottdave]

Re: LG 60PA5500 No VSC or VY Voltage

Thanks, Andrew, I'll try check these and let you know.

[abbottdave]

Re: LG 60PA5500 No VSC or VY Voltage

1. Measure the M5V and see if it is remaining low...If it is then you have a Main Bd problem.

Steady 5V and M5V on the power supply board, ZSUS and YSUS.

2. See if you are getting 15V from Y-SUS Bd to the X-PWB.

Which is the X-PWB?


3. Check if you have 5V and 17V to the Control Bd.
I have steady 5V at positions 4-6 at connector P105 on the Control Board. I have 17V from the power supply to the main board, as well as 5.2V. Where should the 17V be present on the control board?

4. Look for presence of 3.3V from Control Bd to the X-PWB.
Where on the Control Board?

[Andrew F. Ali]

Re: LG 60PA5500 No VSC or VY Voltage

1. M5V is OK.
2. X-PWB are the long boards at the bottom of the TX near the speakers.
3. 5V and 17V should be on one of the pins on the Control Bd jacks.
4. 3.3V should be on one of the pins on the Control Bd jacks to the X-PWB.

[abbottdave]

Re: LG 60PA5500 No VSC or VY Voltage

I have 3.3V at the first pin of all three connectors (P102, P102, P104) on the ribbon connectors that go to the X boards at the bottom. Also, Va (55V) on the two-wire black-and-white jumpers from the YSUS board and the X boards.

I have 16.2V at pins 1 and 2 (marked DD) at connector P105 (the ribbon cable that goes to the YSUS board), and 5V at pins 2, 3, and 4.

VY (on the YSUS board) jumps between about 8V and 24V, about every half-second. VSC varies between about 1.2V and 9V - the higher voltage increasing to 9V and decreasing to about 2V, then climbing again, every 20 seconds or so.

[ReeceyBurger123]

Re: LG 60PA5500 No VSC or VY Voltage

Remove all buffers and retest Vsc.

[abbottdave]

Re: LG 60PA5500 No VSC or VY Voltage

Thanks for your input. With both buffer boards disconnected, VY is now 185V (spec), but VSC is a steady zero.

[ReeceyBurger123]

Re: LG 60PA5500 No VSC or VY Voltage

Buffer is failed replace it. Also resolder Erc coils on Xsus.

[Andrew F. Ali]

Re: LG 60PA5500 No VSC or VY Voltage

buffer is failed replace it. Also resolder erc coils on xsus.

+1

[ReeceyBurger123]

Re: LG 60PA5500 No VSC or VY Voltage

I also suggest adding a fan to the Cpu heatsink and reapplying its thermal paste with thermal silicon help keep that from failing junk Tv's these are.

[abbottdave]

Re: LG 60PA5500 No VSC or VY Voltage

Both buffers have been replaced. That's not to say I didn't get faulty boards, but. . . Also, if the VSC voltage is generated on the YSUS board, how would replacing the buffers make it generate a voltage? Also, are you talking about the CPU(s) on the control and main boards? Right now, there are no heat sinks in place.

[ReeceyBurger123]

Re: LG 60PA5500 No VSC or VY Voltage

If Vsc was failed with the buffer in but working with no buffer it means the buffer is short and loading it down so the smp is shutting down Vsc. Also yes heatsinks on the mainboard and control board.

[abbottdave]

Re: LG 60PA5500 No VSC or VY Voltage

VSC was NOT present with the buffers removed. VSC voltage was zero with the buffers removed.

[abbottdave]

Re: LG 60PA5500 No VSC or VY Voltage

After taking a break from this, I'm ready to try again. I've had the YSUS board checked, and found no problems. Here is a little more information. With the buffer boards disconnected, I do get a good VY voltage (185V), but with the leads +to+ and -to-, it gives a positive voltage. The tag says VY should be -185V. Also, Vsc in still nonresistant. One other thing. I've never had any sound on this - no static, no hum, nothing. With no video I can't change the inputs to even see if it's getting a signal to produce audio, but, nothing. Could the main board, that houses the audio, be causing my no Vsc voltage problem as well?

[abbottdave]

Re: LG 60PA5500 No VSC or VY Voltage

Should read "Vsc is still non-existent".

[ReeceyBurger123]

Re: LG 60PA5500 No VSC or VY Voltage

Vsc is Vy on Lgs my bad. Also buffer is failed in your case replace it.

[abbottdave]

Re: LG 60PA5500 No VSC or VY Voltage

Don't mean to cause problems, but Vsc is not VY on an LG. I'm no technician, but the label shows readings for both Vsc (150) and VY (-185). In addition, there are two test points on the YSUS board, clearly marked VSC and VY.
Buffers have been replaced (and checked). With the buffers removed, still no Vsc.

[dick_barton]

Re: LG 60PA5500 No VSC or VY Voltage

Check the components on both sides of the board around the transformers. There are also fuses on the board fs202 is one I can see but there are probably more.

[maxvalutech]

Re: LG 60PA5500 No VSC or VY Voltage

Surely its a Y board problem as the scan voltage is produced from the Vs. So yes check all components back from Vsc test point.