Philips 32PFL3505D/F7 No Power

[neilc6]

Shares boards with 32PFL3515D/F7 Power board is A01F2MPW

Service manual with schematics available https://www.manualslib.com/download/...l3505d-F7.html

Fuse is not blown. No 34VDC at the output of the transformer.

Diodes D601-604 not shorted on primary side. D638 not shorted as mentioned here on previous thread here https://www.badcaps.net/forum/showth...2pfl3505d%2Ff7

Checked a few diodes around the transformer and not shorted. I should check every one.

I am open to replacing the whole board but nothing available on SJ or ebay. Any suggestions? Are the usual suspects shorted diodes?

[jondoe]

Re: Philips 32PFL3505D/F7 No Power

The service manual suggests if there is no 34VDC;

Check if there is any leak or short-circuiting on the
primary circuit component, and service it if defective.
(C605, D601, D602, D603, D604, Q601, Q602,
Q603, Q604, IC602, T601)


Is there power reaching the big fat capacitor on the hot side?

[neilc6]

Re: Philips 32PFL3505D/F7 No Power

I was checking continuity on some traces and found an open circuit between the pin 1 connector going to the inverter board and the big cap. I then notice the PCB is actually cracked in that section. You can see some cracks in the pic between the power resistors and big cap. Since it is a single sided board, I will bridge some connections with wires to see if it can be fixed without replacing the whole board.

Edit: The jumpers worked. I had to jumper all three lines on the inverter power connection to the lower part of the board acrosss the crack. The reason there was no power is because the ground had been broken between two parts of the primary circuit.

[jondoe]

Re: Philips 32PFL3505D/F7 No Power

I didn't notice the crack till you mentioned it, thats odd, must have had some trauma?

[neilc6]

Re: Philips 32PFL3505D/F7 No Power

I let it run for a couple of hours, turned it off and when I turned it back on, the logo came up and it shut off. There is another thread on this problem in this forum without a solution.

I found this post in a philips forum archive -
"I found the problem in my 32PFL3505D/F7. When the philps logo is displayed the backlighting is turned on. The backlight is powered by it's own board called the inverter board. There are several error signals that can shut the set down. One of them, PROTECT3 is generated on the inverter board when it detects a problem. That could be that a bulb is our or if an over-voltage is detected.

On my set the overvoltage was tripping about 1 second after backlight power was applied. That was just long enough to see the philips logo. It appears the main DC power on the inverter board was supposed to be about 85V. Mine was around 100V, which is right at the OV protection voltage.

It appears that the design did not allow for component aging. It's also quite possible the voltage was always high, but not quite high enough to trip the OV protect. I was able to set my voltage back down to the upper 80V range by adding a resistor. If the components continue to age, this may only be a temporary solution. (of course the only permanent soln would be a better design.)"

So I need to figure out what he did to drop the voltage down.

[neilc6]

Re: Philips 32PFL3505D/F7 No Power

I took some measurements and confirmed the PROTECT3 line goes from 0V when the backlight is on to 0.9V when it shuts down. The power rail is set on the inverter with a 100V zener so the post I quoted confuses me. There should be 82V on an optoisolator dropped down with a resistor as marked on the schematic.

I found some youtube videos in repairing a backlight problem by replacing a transistor I think but not sure if it's the same issue since I don't speak Spanish. https://youtu.be/TIPYn3m7s90

Also not sure if inverter board replacement will fix this. Contact SJ and they aren't offering technical support.

[neilc6]

Re: Philips 32PFL3505D/F7 No Power

Followup since I was able to repair this TV. The schematic prints nominal voltages on transistor pins and has block diagrams which greatly helps debugging. The PROTECT3 line on the inverter board should be 3.4V and can be pulled down low by three separate circuits (Q1600, Q1621, Q1972). In this case Q1972 was on during power up. The circuit here samples the 100V power rail through a divider (0.31x) and drops it down through a 33V zener D1971 (30.32 - 31.88V from the datasheet). The measured voltage at the zener cathode was 28.7V so the zener had conducted at below spec. Removing D1971 should confirm the TV won't enter protection mode.

[RCA2000]

Re: Philips 32PFL3505D/F7 No Power

And the CAUSE.. of the shutdown, which is due to the inverter B+ going to OVER 100 volts..(when it should be 82 volts)..is a BAD Q)-1970 transistor.

If this transistor is checked it WILL likely show Ok...BUT..it is failing in a THERMAL way..when it is COLD..evidently it does NOT conduct enough..allowing excessive voltage to the optocoupler IC 930..as it WARMS up...this voltage WILL DROP..but NEVER quite to the 82 volt level..more like 90-93 volts..but MAYBE low enough..to NOT cause shutdown.. I suspect this is why the set will "sometimes stay on" if one repeatedly turns it back on after it shuts down..the transistor warms slightly and conducts a bit..dropping the B+ to a BIT under 100 volts..so the set stays on. Heating the transistor WILL show it changes as it gets hot--and cooling will show the reverse.

[RCA2000]

Re: Philips 32PFL3505D/F7 No Power

The power rail is set on the inverter with a 100V zener so the post I quoted confuses me. There should be 82V on an optoisolator dropped down with a resistor as marked on the schematic.

Pretty sure...that "100 volt zener diode" right off of the output of the B+ supply on the inverter board is for a CROWBAR..as a "just in case" the B+ goes out of control. This is so it does not get to a catastrophic level. The zener WILL SHORT...if the voltage tries to go much above the 100 volt level...and shut the set down altogether.

Control of the b+ level is established through Q-1970...which controls an optocoupler IC-1930.. A voltage divider off of the B+ line, along with zener d_1970, a5.6 volt zener, sets the bias for Q_1970..

[turbo9000]

Re: Philips 32PFL3505D/F7 No Power

Thank you RCA2000 & neilc6, this was precisely the problem with my DS4A 32PFL3505D/F7. The symptoms identically matched the ones outlined by neilc6 and, sure enough, after taking a hairdryer to Q1970 as per RCA2000, the set powered on.. with a B+ of around 93V.

Q1970 is listed as a KTC3200-GR-AT/P, which seems to be discontinued - "There were issues with the early production of the KTC3200's, especially when used in a driver application with current approaching their SOA ratings - they tended to fail!
KEC at the time claimed that it was due to impurities - we'll never know: KEC then brought out the KTC3201 as a revised die/process - this worked fine." from http://www.diyaudio.com/forums/parts...ml#post3842750

Local suppliers don't carry the KTC3201. When it comes to repairs of this nature I'm certainly not knowledgeable enough to evaluate a part substitute. What could I use instead?

[turbo9000]

Re: Philips 32PFL3505D/F7 No Power

After some hunting & datasheet comparisons, I went for an NTE26, carried by a local supplier (a1parts.com) for $2.10 - can't go wrong! B+ now sits at 82V and the set runs just fine. Many thanks once again!