Philips 37PF7321/98 cannot turn on

[john_doe]

Re: Philips 37PF7321/98 cannot turn on

silly question
are you sure it is 125 and 95 or did you maybe not see a decimal point which might make it 12.5 and 9.5 ?

No error. It is 125vDC and 95vDC.

How can I check the supply voltage from the transformer?

[bammbammfran]

Re: Philips 37PF7321/98 cannot turn on

Is the supply coming from the transformer?

try unplugging the 4 pin plug at 1304 that comes from the power supply and see what that does

[john_doe]

Re: Philips 37PF7321/98 cannot turn on

try unplugging the 4 pin plug at 1304 that comes from the power supply and see what that does

Still 125v and 95v.

We take a rest and continue tomorrow.

[bammbammfran]

Re: Philips 37PF7321/98 cannot turn on

Still 125v and 95v.

We take a rest and continue tomorrow.

from the bottom view, I thought there was a part at 3509 that could have caused issues, but it isn't there

yes that voltage comes from the transformer
I do not know if the diode at 6504 could be causing this ?

you can try to compare resistance on that diode against the 6140 one
they are different but this might tell us something ?
also check the caps at 2508 and 2140 if you have a cap tester mode

we might have to try to reconnect where we cut the trace at the gate of the 7531 to see is a draw on that voltage will reduce the voltage
I would do that with one of your spare fuses and some wire

another way to put a draw on that line that might give us an answer, would be with a 12 volt automotive bulb wired to the 95 and to a ground

[budm]

Re: Philips 37PF7321/98 cannot turn on

That is high voltage and very low currents section used for tuner (34V tuning voltage), the max load on that line is little less than 2000 Ohms (R3509), and other high Ohms Bias resistors for MOSFET q7131, 7531.
I would check the voltage on C2118 (12V) to see if that voltage is also too high.
It is either error in measurement or it has lost regulation which will make all the output on the windings to be too high.

[bammbammfran]

Re: Philips 37PF7321/98 cannot turn on

there is no cap at 2118 and since 5112 and 6113 are not there even the pads will not show power

Just to keep things interesting: This schematic has a lot of parts shown that are not even on the board !!

[budm]

Re: Philips 37PF7321/98 cannot turn on

So there is no 12VSTBY section then? You sure do have lots patient on helping troubleshooting this thing then.
Follow-up, I just look at the picture of the top side, lots of NO LOAD components, sucks.

[bammbammfran]

Re: Philips 37PF7321/98 cannot turn on

yep !! Missing a lots of stuff that is shown in the datasheet
pdf below is just part of it that I marked

Long story !! Short
power supply was not fully turning on, tracked to relay not turning on because 7531 gate was not charging. {Had no voltage and not grounded}
I was thinking of running 5 to the gate, but we decided to try grounding it first (thought it was safer - NOT) {This was all before I had seen an actual schematic}
Grounding the gate turned the 7531 on, but then the gate jumped to 20v and 7531 froze up so removed 7531, replaced it and cut the gate trace since it was pumping 20, then the gate trace started showing 84v and then after a snafoo on the high power side is now showing 95v

so I am trying to figure out what on the 12v line could cause that voltage increase like that after grounding it ?? One would think that something would have blown out and we would have lost voltage instead of getting 7 times more. (maybe something to sell to the power companies !!)


time to cut our loses ?
I just found one on ebay (I had found some last week, but they either did not have the audio section or that had more stuff ??) all with the same numbers ???
I JUST found this one by accident and THE PRICE IS RIGHT !!
http://www.ebay.com/itm/AUDIO-STANDB...item27d0d91f28


Still !! Would have liked to know ! WTF happened

[budm]

Re: Philips 37PF7321/98 cannot turn on

Q7531 is the N-ch and is hooked up as Source follower so grounding the Gate should not turn it on, since the Source which is the out put for the sw5V, that means the GATE Voltage must be at least 5V + Thresshold voltage (typical around 3V) so the min voltage at the Gate must be at least 8V, in this case it uses 11.7V turn on the MOSFET.
This Q 7531 can be shutoff by two devices, one is the PS_ON/OFF Q7532 which will ground out the bias voltage (~35V) through R3121, 3153 through D6133, Q7532 to ground when Q7532 is turn on, this transistor should be off when TV is ON , and it is on when the TV is OFF.
The second shut off is the protection circuit in case the 5V3 goes beyond 6V, which will cause the Zener Diode Z6149 (6V ZENER) to conduct which will turn on Q7140,which will Ground the Gate to ground (Collector of Q7140 is connected to Gate of Q7531.
So the OP must have grounded wrong place since that GATE is made to be grounded if there is problem with 5V3 supply.
Since you indicated that there is no Gate bias voltage, then you need to find out if Q7532 or Q7140 is stuck on (being turn on, or shorted) or not. Or those 3 bias resistors R3121, 3153, 3159 are open.
Also the Clamping circuit D6148, R3142, R3175. D6148 is normally off, if it is on (if +11V not present) then you will have voltage divider consists of R3121 (22K _+35V feeding side) + 3153 (22k) + R3159 (47) + D6148 (0.6V) + R3142 12K (Ground side), that means the Voltage at the Gate will be about 5~6V (Vf of D6148 +V drops of R3142).

[bammbammfran]

Re: Philips 37PF7321/98 cannot turn on

Thanks Bud
I figured grounding the gate would not hurt it, but for some reason, It did fire up ?? OP said that he did the same once replacing that 7531 and it turned on again , but the gate trace was cut at that point, so it did not seem to short it out this time
but that 7531 still seems active even with a gate voltage trace cut out ??
right now it is showing 5 on the drain 5 on the source and 6 on the gate .

Hum, Now that I type this, I wonder if the diode between the gate and source is causing a loop, so grounding it again should shut it down ?

still wouldn't explain the 95 volt issue


This is making good use of some idle brain cells and maybe killing off a few others !!

[budm]

Re: Philips 37PF7321/98 cannot turn on

If the GATE is floating, it can easily be turned on just by touching it with your fingers because it has high impedance and the internal cap gets charged up, it is similar to when you touch the audio input jack of the amplifier and you can hear the hum though the speaker.
He should look at the 5V3 volt line to see if it is higher than normal since it is generated by the same transformer. He should also check the DC voltage along that bias resistor string to see what they have on each legs starting at the top resistor R3121.

[john_doe]

Re: Philips 37PF7321/98 cannot turn on

yep !! Missing a lots of stuff that is shown in the datasheet
pdf below is just part of it that I marked

Long story !! Short
power supply was not fully turning on, tracked to relay not turning on because 7531 gate was not charging. {Had no voltage and not grounded}
I was thinking of running 5 to the gate, but we decided to try grounding it first (thought it was safer - NOT) {This was all before I had seen an actual schematic}
Grounding the gate turned the 7531 on, but then the gate jumped to 20v and 7531 froze up so removed 7531, replaced it and cut the gate trace since it was pumping 20, then the gate trace started showing 84v and then after a snafoo on the high power side is now showing 95v

so I am trying to figure out what on the 12v line could cause that voltage increase like that after grounding it ?? One would think that something would have blown out and we would have lost voltage instead of getting 7 times more. (maybe something to sell to the power companies !!)


time to cut our loses ?
I just found one on ebay (I had found some last week, but they either did not have the audio section or that had more stuff ??) all with the same numbers ???
I JUST found this one by accident and THE PRICE IS RIGHT !!
http://www.ebay.com/itm/AUDIO-STANDB...item27d0d91f28


Still !! Would have liked to know ! WTF happened

I would love to get a replacement standby audio board just to make comparison, but they do not ship to where I am.

Yes, bammbammfran has incredible patience! I thought he would have given up guiding me long ago. Even if we can't get the tv up and running, knowing that someone is willing to spend his precious time to guide me although he gets nothing back in return, humbles me.

Thank you very much, BAMMBAMMFRAN!

[budm]

Re: Philips 37PF7321/98 cannot turn on

Please check the DC voltage on caps C2510, C2512 for the 5V3 standby to see what you have.

[bammbammfran]

Re: Philips 37PF7321/98 cannot turn on

this one is more money but it looks like they will ship to you for $5US

http://www.ebay.com/itm/GENUINE-AUDI...62b1b#shpCntId

[bammbammfran]

Re: Philips 37PF7321/98 cannot turn on

some info for bud

More missing stuff !!
The 34 volts for the tuner isn't coming off of this section of this board
I first looked at the boards on both sides and saw no direct connections via traces and or jumpers , so I started looking for parts and guess what.. the 7511 mosfet and 6511 diode are not there !!
Looks like that power is probably coming direct from the power supply via a cable to run the tuner

[budm]

Re: Philips 37PF7321/98 cannot turn on

Darn, I think its time to get a new board.

[john_doe]

Re: Philips 37PF7321/98 cannot turn on

this one is more money but it looks like they will ship to you for $5US

http://www.ebay.com/itm/GENUINE-AUDI...62b1b#shpCntId

I will get this board. Thanks Bammbammfran for searching.

[john_doe]

Re: Philips 37PF7321/98 cannot turn on

Please check the DC voltage on caps C2510, C2512 for the 5V3 standby to see what you have.

Both are both 5v. C2508 is 85v.

[bammbammfran]

Re: Philips 37PF7321/98 cannot turn on

The power supply does in fact supply the 35 volts from the 7 pin plug out that is on the side of the board with the round red fuse.

So with all the parts that were not installed on that model standby board at the factory, it looks like that 12 volt line (which is now 125) that is created from the transformer pin 6 may have only one purpose, and that is to power up the 7531


Hey, we are down to 85 volts !!
Seems to be the issue is right near that transformer
possibly the transformer or the 6504 diode , possibly the 2507 cap ?
if you want to keep playing and since we can get a replacement, remove the 6140 diode and see if the 125 stays there at the 2508 capacitor, if volatge does stay, try removing the 2507 caps one or both legs and if still too high of voltage, put the diode from 6140 in place of the 6504

[john_doe]

Re: Philips 37PF7321/98 cannot turn on

The power supply does in fact supply the 35 volts from the 7 pin plug out that is on the side of the board with the round red fuse.

So with all the parts that were not installed on that model standby board at the factory, it looks like that 12 volt line (which is now 125) that is created from the transformer pin 6 may have only one purpose, and that is to power up the 7531


Hey, we are down to 85 volts !!
Seems to be the issue is right near that transformer
possibly the transformer or the 6504 diode , possibly the 2507 cap ?
if you want to keep playing and since we can get a replacement, remove the 6140 diode and see if the 125 stays there at the 2508 capacitor, if volatge does stay, try removing the 2507 caps one or both legs and if still too high of voltage, put the diode from 6140 in place of the 6504

I have measured the diode 6140 and 6504 out of circuit and using the diode mode on the tester, they both have 0.4v and the resistance are 1.7 Mohm in only 1 direction.

I cannot get any voltage from the transformer on the secondary side. Using pin 10 as ground, pin 6, 7 and 8 are 0v. Is this correct?

Transformer's primary side pin 3 and pin 5 are 334v.

Cap 2508 and 2140 are ok, I measured out of circuit.

With all connectors removed except 1306, C2508 drops to 54v.