Philips 40PFL4707 SMPS fuse blown.

[genuineguy]

Re: Philips 40PFL4707 SMPS fuse blown.

Dear Forum Members
Some good news. I may have done some wierd debugging and burnt few components, but looks like I have managed to get the board finally working.
Apart from repairing, my intent was to study and understand the entire circuit so I did debugging separately, and this helped me to get a decent understanding of the circuit.

The entire primary and secondary is now connected, the fuse does not blow and I do get 3.3v at pin11 of CN501. As per the manual, this is correct behaviour. If I short the pin11 3.3v to P-ON-H1 and P-ON-H2, the SMPS will start in full power mode.

Now, a question
1. Do you suggest me to connect this board to the entire TV and have TV as a proper load and then start the TV ? Doing this scares me a bit as not sure if the SMPS is fully repaired and working in full power mode. and I have no intentions to damage the rest of TV
2. Or do you think I should connect a dummy load resistor across the secondary outputs to simulate the TV load ? I am slightly worried and thinking on these lines because if I start the SMPS in full power mode and if there is no load, there may be some surprises and blow something again in SMPS

[genuineguy]

Re: Philips 40PFL4707 SMPS fuse blown.

A generic philips training manual clearly says to short the P-ON-H1 and 3.3v so I shorted it and got perfect +24v at the main secondary output. So yes, the SMPS is now working. Will connect it to the rest of TV and report back final results tom. Good night

[genuineguy]

Re: Philips 40PFL4707 SMPS fuse blown.

Current status

1. The SMPS connected to the TV and it turned on. I played a movie on it for about 1 hour and it worked perfect. full volume

2. Unfortunately, there are still issues. If I turn off the TV and immediately turn on, it gets into the bootloop. Shows philips logo, turn off, again logo. If I wait for about 2 to 3 minutes and then turn on, the TV functions normally. Is this behaviour suggesting some faulty capacitor on the main board or even the SMPS ?

[CapLeaker]

Re: Philips 40PFL4707 SMPS fuse blown.

I would say it is a main board problem. Check the PSon. My guess is that if you force the PSU on, it will stay on all day and night. Maybe there is a firmware update for the main board?

[genuineguy]

Re: Philips 40PFL4707 SMPS fuse blown.

There is no firmware update for this model on the Philips support page. I had a very close look by a magnifying glass on the main board but could not see some basic obvious faults like a leaking/burst capacitor.

The behaviour now has changed a little bit.

1. Once powered on, the TV works fine even for 12 hours continuously
2. Using remote, turn off and immediately turn on, it shows the boot philips logo and then shuts down. After this no response to anything from remote, even the power button on backside of TV. I have to turn off the mains power, wait for about 45 sec ( and i hear a very feeble click sound near the boards) and then power on and every thing works fine..
Now, its no more boot looping at the philips logo.

[genuineguy]

Re: Philips 40PFL4707 SMPS fuse blown.

Some more updates.
I left the Tv running for another 12 to 15 hours non stop over night. Post that the TV is properly working. No more power off/stuck at the philips logo. I tried it several times and same result. I even turned off mains, waited for 30min and got perfectly working TV. no more boot loops.
I will keep it mains off for 12 hours to let it cool and try again. hope it works.

Not sure what happened. If it was a software glitch, may be the microprocessor got its counters reset properly in 12 hours continuous run and now works fine.
If it was something to do with some near end life capacitor or component, i think its got to life due to the heat/long on...

or may be the TV decided to behave well with me have mercy on my efforts

[genuineguy]

Re: Philips 40PFL4707 SMPS fuse blown.

After 3 years, I am back to the same forum with the same TV..

After my last post, the TV worked for few days and then had the same issue - Power On, philips logo, shutdown.
Kept the TV aside for another vacation experimentation. Never got time.

Last week, decided to give one more try... I see the following sequence
1. Mains power on
2. Front panel white led blinks 6 times
3. Philips logo display
4. TV shuts down immediately
5. Nothing happens
6. Have to power off and then wait for few minutes to experience same repetition.

Last two days, tried several times, only once the TV started and after 10 minutes it did auto shutdown as there was no input signal connected.

Does this indicate issues with SMPS or main cpu board ? Even if its faulty, how did it start once ?

[genuineguy]

Re: Philips 40PFL4707 SMPS fuse blown.

The current experiment log

1. Removed all connectors. Cleaned all three pcb with liquid cleaner. Cleaned all connectors externally and internally ( holes) using painting brush. Allowed everything to dry.
2. Reconnected
3. Started. This time, went past the Philips logo. I could connect a macbook via HDMI and play youtube videos on the TV for ~1 hours.
4. Using remote, entered service mode and initialized ( factory reset) the TV
5. For 1 hours of proper run, measured voltages. LED+24v was showing properly at 24v, AL+3.3v was at proper 3.3v and the P-ON-H1 was properly at 3.3v
6. After about 1 hrs, the screen shut down. The LED+24v is showing at 6v, AL+3.3v at 3.3v and P-ON-H1 is a 0v. This indicates the main cpu board has turned off the P-ON-H1 signal.
7. Power off, wait for 2 min. Power on... same philips logo and TV shuts down. Problem repeats.
8. Firmware is Code TVNB010_00_PF_XX91_BA PIC code U10_CM08:_40A_C7W_R_02. Did a google search and found no references if this firmware needs any upgrade.

requesting experts next steps to root cause the issue. I suspect the main board is bad and the SMPS is good. Capleaker advised the same. What if I manually put a wire from AL+3.3v to P-ON-H1 ? will the TV be on or is it risky ?

[genuineguy]

Re: Philips 40PFL4707 SMPS fuse blown.

Experiment Log

1. The boot loop continues to be an issue. At times the philips logo shows up once and then the screen goes blank. Nothing happen. Power off-on cycle is required to get to the logo again. Some times the philips logo shows in loop ... 3 times.. 4 times or even 10 times before the screen goes blank and loop stops

2. One wierd method I found to get the TV working. If I keep the TV power cable connected to the power socket on the wall and power switch OFF, overnight.. next day morning I turn on power switch, the TV goes past the philips logo and I can play youtube videos by a mac. This is wierd but its happening for last 3 days. I dont know how is this helping the TV to start

[genuineguy]

Re: Philips 40PFL4707 SMPS fuse blown.

Experiment Log

Decided to study the various pin voltages to get some clues

1.Mains power turn off.
2.All voltages dropped to zero except AMP+24v and AMP+21v( its actually AMP+12v). Both gradually went down and took several seconds to come to zero.. may be 30 sec. Power on and the TV started nicely. No boot loop. I think the AMP+24v and AMP+21v should go down to zero in 1 or 2 sec max. I suspected some of the resistors may have gone higher in resistance
3. R210 is 22K. Connected a new resistor 1.2K 1W in parallel to R210
4. R425 is 10k. Connected a new resistor 1.2K 1W in parallel to R425
5. After the above changes, tried at least 25 times. Every time I do a Mains power off, wait 5 sec, Main power on cycle, the TV starts 100% of the time. No boot loop is observed. Even if I turn off the TV using the TV power switch, or using remote power switch, the TV turns off and then if turned on using TV power switch or remote, the TV starts almost all the times (>90%). Only on few occasions, TV goes in logo boot loop
6. However, the sad news is that if I connect laptop using HDMI cable or VGA cable, the TV goes in boot loop if TV power switch or Remote power switch is used to turn off, wait 5 sec and turn on. However, if main power cycle is done, the TV ~50% times turn on and ~50% times gets in boot loop
7. Experts on various TV repair forums are suggesting that I should try to reflash the memory. I did a search all over internet but the firmware of this TV is not downloadable anywhere. Logically, if the memory sectors are bad, they should fail all the times. But my experiment show mixed success and failures

Any suggestions ?

[genuineguy]

Re: Philips 40PFL4707 SMPS fuse blown.

uploading the service manual for this TV for reference

[genuineguy]

Re: Philips 40PFL4707 SMPS fuse blown.

Experiment Log

1. Noticed IC3003 voltages not normal. Its a 5.5v regulator and takes P-ON+21v(12v) as input. During normal operation, Vin=12v, Vout = 5v, EN=3.3 to 4v. This is expected.
If I turn off the power switch on the TV, Vin=3.3 Vout= 0.8v EN=0v. This is not expected. If EN=0, the Vout should be 0v. This indicates slight malfunction of MP2305 IC3003 regulator. I have connected a 1K 1W resistor from P-ON+5v (Vout of IC3003) to gnd. This has made a positive effect. The Vout is now 0.22v. ( should go to 0v but it doesnt)
So the following sequence is now success
Mains power on
TV starts properly, 100% attempts. No bootloop
Wait for 10 sec
power off using TV power switch,
wait 6 to 8 sec
power on switch using TV power switch
the TV starts properly. No boot loop observed.
If I power on faster 2 to 4 sec instead of 6 to 8 sec, then bootloop is observed.

should i consider replacing IC3003

2. What is not yet resolved ?
Mains Power
TV now turns on 100% of the time
Wait 30 min to 1 hrs
TV switch power off
wait 10 sec
TV switch power on
Boot loop observed

[genuineguy]

Re: Philips 40PFL4707 SMPS fuse blown.

Experiment log

I suspect LED+24V in the SMPS is not holding on to 24v when the boot starts and backlight LED are turned on. If it does not hold on and drops, it will pull the protect3 line low and the CPU will get in protected mode.

I will try connected a separate 24V supply to the LED driver board instead of the TV SMPS.

[genuineguy]

Re: Philips 40PFL4707 SMPS fuse blown.

Good results. External connection of 24V supply was success. The TV no more got into bootloop. It turned on and worked for several hours.
My analysis seems was correct.

To solve the problem with out external 24V supply, I connect two electrolytic capacitor of 2000mfd to the LED+24V line ( there were two existing 1000mfd capacitor).

The boot loop has disappeared and TV starts perfectly.

Several forums on google suggested the bootloop is a firmware issue but atleast for my TV, it turns out to be a +24V power supply line issue.

[budm]

Re: Philips 40PFL4707 SMPS fuse blown.

I am curious, having all the connectors back in place and then check the resistance between circuit ground and
P ON+12/21
ALL +3.4/5.3
P-ON+24
AMP+24

[genuineguy]

Re: Philips 40PFL4707 SMPS fuse blown.

Very happy to get your attention budm. Here the readings

P-ON +12/21 ----------- 890 ohms
ALL +3.4/5.3 ----------- 700 ohms
AMP + 24 ----------- 940 ohms
LED+24V ----------- 296 ohms
P-ON+24v ----------- 295 ohms

[genuineguy]

Re: Philips 40PFL4707 SMPS fuse blown.

@budm
can you pls let me know your views. The TV is working fine. After many test attempts the boot loop is not seen even once.
I plan to put back the back-cover and send this TV to regular use.