LG 60PG70FD plasma power supply no VA/VS + rebooting

[Biruslapio]

Hello, I'm in possession of this 60 inch plasma, its power supply is defective, everything else is OK, very few people bought this TV so there's little I could find to help me.

I plug AC in, relay clicks ON and a second later it shuts down,repeats like this until i plug it off AC, PFC voltage is 305V stand-by and 384~386V during the cycling.
VA and VS go up to 0.42V.

P815 measures(STANDBY / ON / LABEL)
01 - 0V / 16.52V / 16.5V
02 - 0V / 16.52V / 16.5V
03 - GND
04 - GND
05 - 0V / 12.01V / 12V
06 - 0V / 12.01V / 12V
07 - GND
08 - GND
09 - 5.1V / 5.1V / 5V
10 - 5.1V / 5.1V / 5V
11 - 5.1V / 5.1V / 5V
12 - 5.1V / 5.1V / 5V
13 - GND
14 - GND
15 - GND
16 - GND
17 - 0V / 0V / 5VDET
18 - 5.02V / 5.014V / ACD(AC_detect)
19 - 0V / 0V / RL-ON
20 - 0V / 0V / VS-ON
21 - 0V / 0V / M5V_ON
22 - 5V / 5V / AUTO-GND
I also have M5V for the SUS boards and 5V in SMPSU main controller.
Force 5V into RL-ON or VS-ON pin doesn't change anything.

You see that I'm testing this board without main connected or screwed into the chassi, it is default behavior for LG plasma power boards to start-up in this condition.

I've replaced all optocouplers for confirmed working equivalent, replaced all ultrafast diodes(they were bad after 10 years of work), replaced 2 ceramic PTH capacitors, measured all PTH resistors / SMD capacitors / SMD resistors and they seem OK, desoldered and measured every transistor off the board,no bulging caps, everything looks good.

There are these 4 ICs on the primary side 1 KIA393P(dual OPAMP), SC6200(PWM), ICE1PCS02(PFC), SPF9001(no info) and the main microcontroller at secondary side, NEC D78F9234. When the SMPSU is plugged in AC SC6200 and KIA393P have 18V on their VCC pins, then the relay activates, ICE1PCS02 VCC pin gets 15V but it shuts down with the relay.

What seems to control VS is SPF9001(which is located on a soldered vertical daughter board) and on solder-side is a SMD IC SC6700(no info) that looks like control VA, there is one optocoupler to each one of them.

SMPSU part number is EAY41391501, no schematics to be found, all the service manual for 60PG30FD says is "replace power board", found two instances of repair kits including the SC6200.
I'm at a total loss,but I have an oscilloscope and a good DMM, can provide clear pictures of whatever is needed.

Service manual - https://www.electronica-pt.com/esque...s-pa81c-34623/

[Biruslapio]

Re: LG 60PG70FD plasma power supply no VA/VS + rebooting

bimp,i'm stuck at this repair,i can't find a replacement board for sale here,this should be the same power supply to any 60PG models all around the world.

[tom66]

Re: LG 60PG70FD plasma power supply no VA/VS + rebooting

So VS ON does not go up to at least 3.3V when the set tries to turn on?

I would suggest you may have AC detect fault. I can't remember if it should be high or low, but I had a LG plasma a lonnng time ago that was power cycling and the fault was with the AC detect.

[Biruslapio]

Re: LG 60PG70FD plasma power supply no VA/VS + rebooting

I'm testing only power supply on AC, do i need the mainboard connected to test this?
AC detect is OK as i think it should be,always 5V,that's how it behaves on other LG TV PSU i've tested.
5V into VS-ON does nothing,is it supposed to be 3.3V?

PIN NUMBER / STAND-BY / ON / LABEL
17 - 0V / 5V / 5VDET
18 - 5.02V / 5.014V / ACD(AC_detect)
19 - 0V / 0V / RL-ON
20 - 0V / 0V / VS-ON
21 - 0V / 0V / M5V_ON
22 - 5V / 5V / AUTO-GND

M5V is 5V but the pin M5V_ON doesn't signal anything, also the relay activates but RL-ON is 0V.

[tom66]

Re: LG 60PG70FD plasma power supply no VA/VS + rebooting

You will need the main board connected.

Test all the voltages while the set powers on

I don't know if AC DET should be high or low.

[Andrew F. Ali]

Re: LG 60PG70FD plasma power supply no VA/VS + rebooting

I like to test PSUs with a load. The load I suggest is two 120Vac or 0ne 220Vac household light bulb. Disconnect all connectors except the ac-in connector from the PSU.
Follow these steps:
1. Connect pin 22: Auto-GND to pin 03: GND.
2. Connect a 100ohm resistor across pin 19: RL-ON to pin 09: Std-By 5.1V.
3. Connect another 100ohm resistor across pin 20: VS-ON and pin 10: Std-By 5.1V.
4. Connect another 100ohm resistor across pin 21: M5V-ON and pin 11: Std-By 5.1V.
5. Connect the lightbulb/s across Vs and GND on the connector that would have gone to the Y-sus Bd.
6. Apply the 120/220Vac.
If the PSU is good then the lightbulb/s would light up bright and remain ON.
Measure that all the sub-voltages are produced: Va, M5V. 12V, 17V, etc.
Good Luck

[Biruslapio]

Re: LG 60PG70FD plasma power supply no VA/VS + rebooting

Thank you all for the info.
I grounded AUTO_GND, then did the tests with resistors on M5V-ON RL-ON and VS-ON, same result, click on and click off quickly, removed the VS-ON resistor and the power supply is working without VS and VA.
So now I've found the problem, I turned my attention to the ICs that control VS, the MOSFETs and switching diodes seems ok.
The vertical board is made by sanken and has this SPF9001, found pinout and it doens't measure bad in any way, I was betting on a SMD cap but they aren't shorted.
On the picture of the board itself i circled what controls VA(SC6700) and VS.

[tom66]

Re: LG 60PG70FD plasma power supply no VA/VS + rebooting

Have you checked all fuses and power resistors?

[Biruslapio]

Re: LG 60PG70FD plasma power supply no VA/VS + rebooting

I did and redid that, all are matching their color codes, there is ony one fuse(main AC input) and it is good.

[Beau28713]

Re: LG 60PG70FD plasma power supply no VA/VS + rebooting

Have you checked all solder connections for the the VS circuit. I had a samsung plasma doing the same thing and i couldn't find any issues. I checked the solder connections and found a bunch of cold solder joints and cracks. Reflowed the connections and set powered up. Been using it now for 2 years without any issues.

[Biruslapio]

Re: LG 60PG70FD plasma power supply no VA/VS + rebooting

I have now resoldered everything, zeners, resistors, ICs, found two problems, a 100nF SMD at SPF9001 board was measuring 80nF,replaced, and two diodes were just touching their rivets, not soldered to them or the boards at all, that didn't solve or change the problem.
Strange that both VA and VS go up to 0.41V, same voltage.
Messing with their trimpots changes nothing.
I will now try to measure VCC for the VS controller.

[ben_att]

Re: LG 60PG70FD plasma power supply no VA/VS + rebooting

Hello,

I have a similar model, the tv was unplugged and left for approximately 6 months and was working fine when unplugged. Just tried to use it and it doesn’t work.
I have the exact same board and have a similar issue where it cycles on/off twice before shutting down completely in which case the only way to get it to power up again is to disconnect the AC and allow the caps to discharge.

If I trigger M5V and RL ON the relay will stay energised and I can measure all the other voltages fine (5V, 12V, 16.5V) except VA and obviously VS.
if I put 5V on VS ON and have my meter on VS and GND I read 190VDC for about 1.5 seconds before the unit shuts down and I have to unplug and discharge the caps before I can try again. So I’m assuming given the above there must be some sort of protection circuit related to the VS supply? What voltage should I be reading on VA?
The 1uf MKT caps on the 240 side were bad and replaced those but no change.
Does anyone have any detail on what could cause it to shut down?

Thank

[Biruslapio]

Re: LG 60PG70FD plasma power supply no VA/VS + rebooting

Your issue is different from mine, I get no VS, it is always 0.41V.
PFC problem maybe, or leaking components, replace all the 8 optocouplers first.
I'll swap SC-6200, seems like the only thing that may be causing this issue aside from the main processor, there are 2 optocouplers which never activate(31V between C-E) and goes to VCC of SC6200 and KIA393P, but they already have 20V stable, I don't understand what they are for.

[Biruslapio]

Re: LG 60PG70FD plasma power supply no VA/VS + rebooting

Just bought and replaced SC6200, waste of time.
The amount of swear words I've said to this PSU can't fit in this post, but whatever, I'll just buy a working one, good waste of money on numerous components, the fault now may be either SPF9001, SC6700, KIA393P or the main chip, this all can be resumed in one word, SANKEN, which made these PSUs with only shady top of the line components that can't be found anywhere.

I noticed something, everytime i try to measure the voltage between C-E on two of the optocouplers primary side, the power supply stars behaving erraticaly,I tested it further and only putting any probe at the emitter makes it power cycle exactly as if I flip the VS-ON switch, I've read here too about one user having a really similar fault with a old samsung plasma PSU, but when he touched the opto the power supply started to work, opposite of my case.They lead to KIA393P and SC6200 Vcc pins, both which already have 19V,there is another 19.89V between C-E, I don't know if it should rise when VS-ON kicks in, it never moves activates.

At the image,i mean "until it is untouched".

This is the topic with the optocoupler issue https://www.badcaps.net/forum/showthread.php?t=50156