Reply With Quoteloopyloo (21-07-17)
You could ignore the PFC circuit (Q601,602) as it's just reactive compensation and the main HVDC 340V is getting through OK
Need to check that IC101 is getting VCC of 12V on pin 12 (without getting your fingers burnt) - it's derived from the 3.5V standby supply and turned on by opto IC503 and Q501 when POWER_ON goes high 3.5V
The opto could be bypassed by placing a temporary short across the photo transistor pins 3,4 IC503 to force VCC on.
If VCC is on and no Q101/102 switching happens then IC101 is likely fried but good news is a replacement only costs a few dollars
O - and use the series lamp while doing all this to limit the amount of potential shrapnel if things go sideways
EG Q101 & Q102 both turned on simultaneously would be a direct short across the 340V supply and you'll just get a bright lamp without the smoke and damage
Last edited by Skepticist; 21-07-17 at 11:01 PM.
loopyloo (21-07-17)
Followed your directive ... No 12v on IC101Originally Posted by Skepticist
I'll check pin 5 of T501 next.
Need to pull up POWER_ON to +3.5V rail to get the 12V VCC supply to turn on if that switching cct is all OK
Pin 5 of T501 will be alive and well high frequency chopped waveform if the 3.5V supply is working - better place to check would be the collector of Q501 or pin 4 of opto IC503 for >12V DC
Last edited by Skepticist; 22-07-17 at 04:14 PM.
loopyloo (26-07-17)
Nothing on Q501's collector.
Couple of questions :
The triangle symbol is ground isn't it ?
The cut-off corner of the regulators denotes pin 1, true ?
at the risk of being wrong, that could be ground but not chassis but a floating gnd. The chamfer end I would think would be 1, It is on a rectifier. What regulator? datasheets?
loopyloo (26-07-17)
true and true
Sometimes they'll make a distinction between circuit ground and chassis ground as you'll see on the schematic there's a different 'earth' symbol on the secondary side to the one on the primary side. In this case the primary side 'earth' is not actually connected to the mains earth and it's simply the -ve side of the rectified mains that's common to everything (on the primary). The different grounds are connected only by an LC circuit (LB105 in series with CY107) so you need to use the correct ground reference for side of the supply you're measuring voltages on because those 'grounds' are essentially floating.
No voltage on Q501, is that when the 3.5V DC supply is present?
and any sign of activity on that pin 5 of T501? (the frequency and waveform is likely to give strange readings)
All the VCC supplies on the primary side are derived from that winding on T501 (pins 4 & 5)
Last edited by Skepticist; 22-07-17 at 10:58 PM.
loopyloo (26-07-17)
Sorry yes, slip of the keyboard.
I did mean rectifier.
Yeah well I miss read the diagram then cos if I reference to to the rectifier (-) Q501 has 16v on it.true and true
Sometimes they'll make a distinction between circuit ground and chassis ground as you'll see on the schematic there's a different 'earth' symbol on the secondary side to the one on the primary side. In this case the primary side 'earth' is not actually connected to the mains earth and it's simply the -ve side of the rectified mains that's common to everything (on the primary). The different grounds are connected only by an LC circuit (LB105 in series with CY107) so you need to use the correct ground reference for side of the supply you're measuring voltages on because those 'grounds' are essentially floating.
No voltage on Q501, is that when the 3.5V DC supply is present?
and any sign of activity on that pin 5 of T501? (the frequency and waveform is likely to give strange readings)
All the VCC supplies on the primary side are derived from that winding on T501 (pins 4 & 5)
No wonder I was having trouble getting readings. I saw the grounds but it didn't click with me that they were different symbols.
I'll go back and do some rechecking now.
Last edited by loopyloo; 22-07-17 at 11:27 PM.
Looking a bit better then - now just need to make Q501 turn on to supply VCC to IC101 & IC601 and see if the VCC voltage holds up. IC101 should start switching the FETs to produce the 12 & 24V outputs if all is ok
loopyloo (23-07-17)
I can see 1 volt on IC 101 pin12 and 1.6v on IC601 pin8.
There is 15v on C509 +side.
PS : I just noticed I forgot to plug in the motherboard cable which has the wire links for poweron and driveon. The above voltages are the same whether it is plugged in or not.
Last edited by loopyloo; 23-07-17 at 01:50 PM.
Starting to look like IC101 (and probably IC601) is fried as that's a major short cct
I'd be trying to isolate the 2 from the VCC supply to test them individually so the supply (and switch cct) as well can be tested for proper function
If you're comfortable with SMD work try then removing IC101 from the PCB without damaging the rest of the circuit (major challenge) and if u decide to try repairing it and I'd be simply abandoning the PFC circuit altogether by disconnecting it from VCC and the 340V bus.
Try lifting the VCC pin off the track to check the IC for the short before trying to desolder the entire package (just to be doubly certain the fault's in the IC and not a peripheral component)
loopyloo (24-07-17)
Thanks for staying with me on this one. I would like to get this going in it's original condition if possible cos I want it in my loungeroom.
I lifted pin12 IC101 but no difference. I'll try IC 601 next. I'm not sure the chips are short unless they become short once powered. I ran the meter over them (power off of course) and couldn't find any short pins that way.
Seems like there's 2 problems since "power_on" is on all the time as well.
The components surrounding Q501 were right next to where the original wipeout occured. I already replaced ZD502 with a 1W version from Jacar (was 500mW) and I think I'll replace C504 and C509 just because.
By the way, SMD C203 (from 3.5v supply) is cracked. Looks much worse when viewed from the side.
Last edited by loopyloo; 24-07-17 at 03:26 PM.
That's the way - eliminate every possible source of the short before going for removal of the smd ICs
I'd be checking how VCC holds up without the ICs connected just to be 100% certain both or either one is the problem
The PFC circuit is what I'd class as non-essential especially when fault-finding and, if the fault is in that particular circuit, I'd just disable & bypass it permanently (very non-green I know
Last edited by Skepticist; 24-07-17 at 09:17 PM.
loopyloo (26-07-17)
Swapped out the cracked cap C203 for a 102 ceramic disc, and changed C504, C509 and C510 since it is right next to the others.
No change to the measurements.
Then I lifted pin8 of IC601 and now things are different. Gotta do some more voltage checking and I'll put IC101 back into circuit to see what happens.
Any more suggestions ?
Could turn out to be lucky after all
Does IC601 read as a short with the ohmmeter across VCC & GND with the pin lifted?
PFC circuit can be completely disabled by lifting 1 end of LB601 and keeping pin 8 of IC601 lifted off the track
Last edited by Skepticist; 25-07-17 at 10:59 PM.
loopyloo (26-07-17)
No it doesn't read as short.Could turn out to be lucky after all
Does IC601 read as a short with the ohmmeter across VCC & GND with the pin lifted?
PFC circuit can be completely disabled by lifting 1 end of LB601 and keeping pin 8 of IC601 lifted off the track
Curious and curiouser
But it still looks like the problem (for VCC at least) is in the PFC circuit and is only present with IC601 VCC pin 8 connected? So that IC looks very guilty to me.
Time to fire it up (via series lamp) with just IC101 connected to VCC?
loopyloo (28-07-17)
What's with the LED (green rectangle) ? ... Is it to show stb voltage on ? It never lights.
I can't find it on the schematic.
I went back to the beginning to start with measurements.
Some are obvious but I'll put em here anyway.
All of the following are with the motherboard connected as normal and pin8 of IC601 lifted.
Voltages on the left are stb mode / right are after hitting the 'power on' of remote.
Power on pin = 0/3.5
F101 = 336
Q101 drain = 336/336
Q101 gate = 0/0
Q102 drain = 0/0
Q102 gate = 0/0
T101 pin4 = 0/0
ZD102 cathode = 0/0
Q601 drain = 336/336
Q601 gate = 0/0
Q601 source = 0/0
Q602 drain = 336
Q602 gate = 0/0
Q602 source = 0/0
D510 cathode = 15.6/16
C510 (+) = 15/15.5
C509 (+) = 14.8/14.8
ZD502 cathode = 14.8/14.2
D201 anode = 0/0
D201 cathode = 3.5/3.5
C202 (+) = 3.5/3.5
IC502 pin1 = 3.3/3.3
IC503 pin1 = 3.5/1.2
D251, D252, D259 and Q251 all remain at 0 volts.
The TV reacts the same as before , LED on the front is red at power up then flashes twice when the go button is press. It never turns white (TV on) but it could have been previously disabled in the menu for all I know.
Just ordered an L6599D. Should be here tomorrow and hopefully get some reaction out of the bottom half of the circuit.
Last edited by loopyloo; 27-07-17 at 04:16 PM.
The only LED I can see on the SMPS board is LD701 which appears to indicate activity on IC701 SMD single chip microprocessor with diagnostic interfaces (serial/IIC etc)
It looks like the supply for that circuit (DRV_VDD) requires the 12V supply active so we have to get that (and the 24V) going to progress any further.
The way I'd approach it is to work on the power supply board with it disconnected from the the rest of the TV circuit to reduce the possible red herrings until the power supply is sorted out
Connecting POWER_ON to +3.5V with a temporary jumper wire should force the supply to start up with a good IC101 fitted, then any secondary side problems will present themselves (hopefully none)
The 12V output (main supply) is regulated via opto IC102
Last edited by Skepticist; 27-07-17 at 10:18 PM.
loopyloo (28-07-17)
Yeah Q101 and Q102 are relying totally on IC101 so I'd say it's definitely worth replacing.
No wonder I couldn't see that LED. I didn't look further down for it.
IC101 will be here tomorrow. Interestingly, I could have pulled one from another board, but I wasn't sure how well that pink glue would be holding the chip down. Might have just ended up destroying it. I have a home made copper tip for my iron that I use to desolder IC's one side at a time, but it won't work if the chip's glued down. The other way might be my hot air station but will it destroy the chip ?...maybe.
I can buy a replacement board for around 50-60 bucks but I want to see if This can be worked out first, besides, I'm not sure of the mainboard condition yet, but my guess is it's ok.
Anyway tomorrow will tell a lot. I hope.
Last edited by loopyloo; 27-07-17 at 10:52 PM.
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