Lowry GS32FHD in Standby

[dick_barton]

Hello All,
A friend has just dropped off his Lowry GS32FHD TV which he said was stuck in standby.

Mainboard 17MB35-4 060109
Power supply 17PW26-4 V.1

One turning it on it operated perfectly for about 15 minutes with no noticeable problems before switching itself back into standby.
Using the remote to turn the set back on, after a short delay the backlight flicker on/off and the set immediately returns to standby.

With the power supply disconnected from the mainboard the standby voltages are present.

Jumping PS_On to 0V and BL On/Off to +5V using 1K resistors brings on the backlights with no issues.

Have looked at the data in/out lines of the SPI chip (25L1605D) with an oscilloscope I can see data buzzing on the data in/out lines so I don't believe it to be a failed chip.

Reconnecting the power supply to the mainboard I have the following voltage when switching on out of standby given as an attachment.

I suspect it is a power supply fault with the 24V inverter supply being 22.8V and the 12V supply to the board being only 10.9V.
Voltage at D898 is 329V in standby and 335V out of standby. Schematic says 400V and would explain why the 24V and 12V supplies are slightly lower than they should be.

Would I be correct in saying this is a PFC circuit problem.

Does anyone have a better schematic for this model (17PW26-4 V.1) since I find it hard to navigate around.
Thanks

[CapLeaker]

Re: Lowry GS32FHD in Standby

I agree. The 12V/24V rails are off in voltage and the PFC is off (as not turned on). Your are just on plain rectified mains. Check VCC and gate drive on the PFC. Be careful probing around with the oscilloscope in the primary circuit. But I think you know that already.

I think the PFC may be on the back side of the board (IC802 FAN7529)?
Never mind I found it.

[dick_barton]

Re: Lowry GS32FHD in Standby

Thanks for the confirmation Capleaker. I'll do a component test around that area to begin with and check for any doggy connections in the light that it initially ran for 10-15mins when first powered up.

[budm]

Re: Lowry GS32FHD in Standby

Check PFC Diode D898 (1N5406, next to the Bridge rectifier) for shorts.
Also check D822, 833 next to PFC Q813.

[dick_barton]

Re: Lowry GS32FHD in Standby

Thanks Budm,
Lifted the components out to test D882, D883, Q813 & D898 and all test OK.

[ReeceyBurger123]

Re: Lowry GS32FHD in Standby

Disconnect Psu from mb and apply power with no resistors on anything, you should have 12v,3.3v,5v,24v rails. Had this issue shorted hdmi chip on the mb.

[CapLeaker]

Re: Lowry GS32FHD in Standby

Disconnect Psu from mb and apply power with no resistors on anything, you should have 12v,3.3v,5v,24v rails. Had this issue shorted hdmi chip on the mb.

He already forced it on Reecy...

[CapLeaker]

Re: Lowry GS32FHD in Standby

pin 5 is PFC_OFF btw so probe that too.

[dick_barton]

Re: Lowry GS32FHD in Standby

pin 5 is PFC_OFF btw so probe that too.

Hello CapLeaker
Will do thanks.
Shouldn't the PFC voltage remain stable at close to 400V when it fires up?
If I look at the 400V rail with my meter set to AC volts I can see the voltage peak up to 390V, drop, 390V, drop or is this the PFC IC switching on and then shutting down, switching on, shutting down.
I'll 'scope it in the morning and see what is going on.
Thanks

[CapLeaker]

Re: Lowry GS32FHD in Standby

if the PFC works correctly, you should have 390V DC on the main filter cap.

[dick_barton]

Re: Lowry GS32FHD in Standby

if the PFC works correctly, you should have 390V DC on the main filter cap.

Thanks CapLeaker.
I've 'scoped the controller chip and the waveforms are completely up the creek.
The supply voltage is fine 14.5V. Waveforms below.

I've found a cheap replacement on Ebay and have ordered it. This will allow me to give the TV back and fault find the psu in my own time giving me a spare board.


The waveforms were taken with a x200 probe so 1V on the scale = 200V
Thanks to all for your help.

[dick_barton]

Re: Lowry GS32FHD in Standby

The replacement power supply has just been fitted and set is now up and running.

[dick_barton]

Re: Lowry GS32FHD in Standby

Just for information.

This was an odd fault. I could force the backlights on without the mainboard connected. I could run the set with the backlights disconnected but obviously sound and no picture but I could not run both.
I believe that CapLeaker was correct and it was a failure but not total failure of the PFC circuit.

[vinceroger69]

Re: Lowry GS32FHD in Standby

Thanks for posting the update/fix some boards can be a pain too fix so a board swap is what i usually do too, the old psu with time you maybe able to repair or as always they are usefull for spare parts etc.

[dick_barton]

Re: Lowry GS32FHD in Standby

Hello vinceroger69, Thats my intention to fix it in my own time and have a spare.

[vinceroger69]

Re: Lowry GS32FHD in Standby

Hello vinceroger69, Thats my intention to fix it in my own time and have a spare.

Yes thats what i try to do too and i can learn from more troubleshooting stages etc and i like the challenge too im sure you will fix this given time.

[dick_barton]

Re: Lowry GS32FHD in Standby

Final update.

I removed R817, R818, R819 (all in series) due to having odd readings when in place. Off the board they measured correctly at 619K each. Cleaned up the pads on the board and resoldered the resistors back in place and now all the output voltages are correct.
3.35V, 11.97V, 24.7V with no other boards connected

Looks like I may now have a spare board.

[armoured_smiler]

Re: Lowry GS32FHD in Standby

Hi, Please can you tell me did the resistors still have 'odd' reading when back in place?

"I removed R817, R818, R819 (all in series) due to having odd readings when in place. Off the board they measured correctly at 619K each. Cleaned up the pads on the board and resoldered the resistors back in place"

[dick_barton]

Re: Lowry GS32FHD in Standby

If I recall they do give odd readings when in circuit and it is best to check them out of circuit to confirm their correct values.