Sony KDL-32EX400 fault finding

[t4796]

Hi,

I have a 32inch sony EX400 that powers on with red standby light.
Pressing the power on results in the green light for a short time, then a red light that blinks twice.

I've got the power supply on the bench removed from the television with a switch between the STBY3.3V (pin1) and POWER ON (pin 3) of CN6401.

I have taken the following measurements:

------ STBY | POWER ON
C6325 340V 340V
C6117 7.75V 13.45V
C6118 8.05V 13.89V
Q6201 ------ S-G (2.195) S-D (0V)
PH6103 'power on' across pin1+2 stby (0V) on (1.15V)
PH6101 'AC off det' across pin1+2 stby (0.93V) on (0.95V)
PH6102 'ST-BY 3.3v reg' across pin1+2 stby (0.987V) on (0.987V)

I'd like to try and learn and am happy to take any other measurements anybody suggests.

Thanks for any suggestions

[budm]

Re: Sony KDL-32EX400 fault finding

Good clear pictures of both side of the board please.
If the circuit has PFC Voltage booster, the DCV on the main cap should be >360VDC when PWR-ON (PS-ON) is applied.

[t4796]

Re: Sony KDL-32EX400 fault finding

Thanks for the reply. Here are the pictures. The circuit has Sony A3809AM PFC chip which I see on all the schematics as CXA3809M. I do not see any change in the main cap (it stays at 340V) voltage when I short the 3.3v standby pin to the power on pin.

[redwire]

Re: Sony KDL-32EX400 fault finding

Can you measure the other PSU outputs on CN6401,2,3, like UNREG24V, REG12V to see if they come up. The 3.3V standby regulator seems ok.

[budm]

Re: Sony KDL-32EX400 fault finding

Pin 2 (MODE pin, active LO) of CXA3809M should go low when ps-on signal is applied to turn on the PFC circuit.
You should also check and see the VCC of the CXA3809M.
the switched REG12V, T-CON VCC, and the UNREG 24V power supply section (provided by transformer T6302) requires boosted Voltage from PFC to run.

[t4796]

Re: Sony KDL-32EX400 fault finding

Thanks redwire and budm here's my results:

T-Con VCC, REG 12V, UNREG 12V, all 0v or close enough stby or on.

Vcc @ CXA3809m 7.77V (stby) 13.48V (on)

Pin2 (mode)@ CXA3809m** 0.3mV (stby) -24.3mV (on)

** i took this measurement with red prob on pin 4 of PH6103 and black on -ve of main cap

pin3 (AC_detin) @ CXA3809m** 0.601V (stby) 0.576 (drops a bit initially then slowly to this figure dropping a mV or two every so often)

** i took this measurement after R6305 and black on -ve of main cap
*** i'm not sure how i should have measured this, since it's like the top half of the wave only isn't it and not the bottom? i measured it on dc volts.

Haven't had a chance to digest this yet, just finished

I measure the voltage across each diode D6104 and D6105 and i get 8.0V and 8.3V (stby)/ 13.5V and 13.9V (on). Why do they read different, is it the components after?

[budm]

Re: Sony KDL-32EX400 fault finding

The mode pin does not look like, I expect it to be HI (>2.5VDC) when TV is in standby mode.

[t4796]

Re: Sony KDL-32EX400 fault finding

It says in the CXA3809 datasheet the mode can be set to normal sequence by short circuiting to gnd, or that for standby mode it can be tied to vcc voltage or left open.

Left open is the way it looks in the schematic once you take away all the components marked 'non' which are not on my board. There really isn't anything external apart from gnd it can be connected to via PH6103.

I thought maybe the ac_detin isn't reading high enough voltage to startup the ic?
Is there a way to calculate what I should be seeing at the ac_detin pin? I got confused because one pin of the second smaller bridge rectifier is unconnected.

So there's rectified voltage independant of the main cap? with two diodes reverse biased??/resistor/small 16v cap to gnd, how can I calculate what I should be seeing at this point?

[budm]

Re: Sony KDL-32EX400 fault finding

"It says in the CXA3809 datasheet the mode can be set to normal sequence by short circuiting to gnd, or that for standby mode it can be tied to vcc voltage or left open." If you look at page 6, 11 of the spec sheet, you will see that it has internal pull-up resistor (50K) that is why you can leave it open the ground it with OTPO IC6301, so that mode pin should ne be showing 0V.
AC detection circuit, see page 21 and later.

"So there's rectified voltage independant of the main cap? with two diodes reverse biased?" Yes, and It is not highly filtered dc.

[t4796]

Re: Sony KDL-32EX400 fault finding

ok, so you are saying, the way it is connected internally it should be reading vcc when the circuit isn't connected to ground via the opto coupler and i may have a problem with the chip?

also, i found a foreign forum which had a picture of a guy who had to replace the zener off the ac_det pin that was why i was questioning that part of the circuit and what voltage i should be seeing at that point.

if it's mains, rectified then 1.3meg of resistors then a 12v zener and a regular diode reverse biased (and the resistor) and the zener failed i was trying to calculate the possible scenarios to see if 0.6v could indicate a faulty zener or not.

[budm]

Re: Sony KDL-32EX400 fault finding

It should be > 1/2 of VCC for HIGH when the OPTO is not activated by the POWER ON signal.
What resistance do you get between Mode pin and GND?

[t4796]

Re: Sony KDL-32EX400 fault finding

ok budm, i'll measure the resistance when i get home from work and post.

[t4796]

Re: Sony KDL-32EX400 fault finding

regarding mode pin i have 46.9k between mode pin (2) and ground.

regarding the ACdetin pin, using voltage divider between 33k and 1.32meg we calculated there should be around 8v at the acdetin pin but we have 0.6v. the confusing part is i have only 210v DC after rectifier (before 1.32meg of resistors) but we figure maybe my meter is unable to read it right because the post rectifier voltage is not filtered.

[budm]

Re: Sony KDL-32EX400 fault finding

So that means you should have 1/2 of VCC since pull-up resistor is 50K.

It is pulsing DC (HALF WAVE VOLTAGE and shown in the spec sheet of the IC) so your meter may not show the correct reading.
So all those 3 resistors have the correct resistance? How about Mode ACDET PIN resistance to GND?

[t4796]

Re: Sony KDL-32EX400 fault finding

Thanks for your replies bumd.

I believe the resistance on the ac_det pin to gnd is 32.6k from memory. I'm not sure of the exact resistance because I'd need to lift a pin of the IC to test. Can try that tonight.

The four series resisters from memory the two end ones read a touch lower than the two middle ones. like it might have been something like 31k 33k 33k 31k.

CXA3809M may take some time to arrive might order one now.

[redwire]

Re: Sony KDL-32EX400 fault finding

I would also check the MOSFET Q6301 for shorts and a few other parts around it. In other PSU's, I have seen the PFC MOSFET short, and pop the fusible resistor (i.e. R6321, R6319) and then damage the PFC controller IC.

[t4796]

Re: Sony KDL-32EX400 fault finding

thanks redwire,

i'll check those components out after work.

[t4796]

Re: Sony KDL-32EX400 fault finding

the components looked to be ok (I'd already removed the fet and tested out of circuit) and none of the resistors tested bad.

i ordered the cxa3809 ic and have been waiting for it to arrive, which it has.
i removed the old one carefully and replaced the new one. it was late last night, but i did have time for a quick measure and now i have the voltage at the main cap boosting up to 393v when in the power on mode!

i'll test for the other voltages tonight, but i expect they will be there. in my travels i found a document in spanish i think detailing a process for dealing with power supply issues with these sony units. i'll post it here tonight in the hope that it can help someone else. it also mentions checking for two particular diodes on the board, if they're not there i believe it says to add them (my online translation from spanish to english wasn't amazing).

would be interested to hear how you guys interpret it

feeling good it's almost resolved! thank you guys, i appreciate it!

[budm]

Re: Sony KDL-32EX400 fault finding

I also would like to know what Voltages you are getting on those pins that we made the measurement earlier, that will good info to keep for the future reference.

[t4796]

Re: Sony KDL-32EX400 fault finding

ok here's some before and after! almost everything, i was too tired to complete tonight. i've copied the old values into this post.

BEFORE WITH BAD IC6301

------ STBY | POWER ON
C6325 340V 340V
C6117 7.75V 13.45V
C6118 8.05V 13.89V
Vcc @ CXA3809m 7.77V (stby) 13.48V (on)
Pin2 (mode)@ CXA3809m** 0.3mV (stby) -24.3mV (on)
pin3 (AC_detin) @ CXA3809m** 0.601V (stby) 0.576 (drops)
T-Con VCC, REG 12V, UNREG 12V, all 0v or close enough stby or on.

AFTER IC6301 SONY A3809 REPLACED

------ STBY | POWER ON
C6325 339V 394V
C6117 12.45V 14.02V
C6118 12.41V 14.34V
Vcc @ CXA3809m 12.44V (stby) 14.04V (on)
Pin2 (mode)@ CXA3809m** 12.38V (stby) 93.8mV (on)
pin3 (AC_detin) @ CXA3809m** 5.36V (meter on DC) 1.83V (meter on AC)

Secondary voltages to follow when i've had a sleep