Hitachi LE49S508

[krygods]

Re: Hitachi LE49S508

BL_ON is 0VDC at CON4 when everything is plugged in.

Resistance between collector and GND (Pin 3)? If so it jumps to 150 ohm and drops off right away.

[budm]

Re: Hitachi LE49S508

You need to have BL-ON signal (TV must be turned on) for the Q11 to be ON for it to supply 12VDC to the IC.
"If so it jumps to 150 ohm and drops off right away" When you say drops off, do you mean the resistance goes up higher than 150 Ohms or goes lower than 150 Ohms?

[budm]

Re: Hitachi LE49S508

I just re-read your post 1 again:
CON801
PS-O/F - 3.2VDC ps-on is OK.
PB adj - .14VDC, Dimming signal is also way too low.
PB O/F - 0VDC This BL-ON signal is not present from the main board.
GND
GND
GND
GND
+12v - 12.37VDC
+12v - 12.37VDC
+12v - 12.37VDC
+12v - 12.37VDC

I do not know why I did not catch that!

[krygods]

Re: Hitachi LE49S508

So this one has a main board issue. Possible to troubleshoot the main board?

[CapLeaker]

Re: Hitachi LE49S508

take the pin out from the main board, take a 1k resistor and jumper 5v to BLon.

[krygods]

Re: Hitachi LE49S508

I jumped BL_ON to +5V and there is now +12VDC between Pin 1 and Pin 3 of OB3350CP no standby light though TV doesn't respond to any button input.

[CapLeaker]

Re: Hitachi LE49S508

How much voltage are you getting on the PBadj. pin? If there isn't anything there, do the same trick on that pin too. Don't forget to take the pin out of the connector.

[budm]

Re: Hitachi LE49S508

"I jumped BL_ON to +5V and there is now +12VDC between Pin 1 and Pin 3 of OB3350CP no standby light though TV doesn't respond to any button input." But it sounds like you do not have cable between the power supply and the main board connected, when you do the force on, the wires for the signals must be disconnected so the force on signals will be be fed back to the main board.

[krygods]

Re: Hitachi LE49S508

I have everything connected, only thing disconnected is the BL_ON pin on the connector, it is unplugged and jumped to +5VDC with a 1K resistor. How else would I jump +5VDC to the BL_ON pin? +5VDC is coming from CON901 of the main board.

[budm]

Re: Hitachi LE49S508

OK, you will need to force the PB ADJ pin also since you are only getting 0.14V on that pin.
BTW, check the Voltage on LED connector to see what you get.
At this point we know that you have main board problem due to missing two command signals, no standby LED.

[krygods]

Re: Hitachi LE49S508

Ok so I am also jumping PB ADJ to the +5VDC?

[budm]

Re: Hitachi LE49S508

Yes.

[krygods]

Re: Hitachi LE49S508

Alright, back lights come on now, no standby light. Power at LED+1 is 204VDC. So we've narrowed it down to a faulty main board then?

[budm]

Re: Hitachi LE49S508

Yes, I should have seen those Voltage readings in your post 1, I am sorry for wasting your time troubleshooting the backlights section, but at least we now know how it works in more details in case it goes out in the future.

[fzabkar]

Re: Hitachi LE49S508

I would check U804 (+3.3V LDO), U807 (1.8V LDO), U805/L810 (+5V switchmode?), U700 (multi-output switchmode), U802/L805 (+1.15V switchmode?). Some voltages are standby voltages (+3.3V and +5V), while others are required by the SDRAM (1.8V) and SoC (+1.15V Vcore).

I have found several several service manuals for TVs using the MSD3393LU SoC:







System_Reset (pin #95 of SoC) should be low when the SoC is running and high when it is in the reset state.

Panel_On/Off is pin #94 of the SoC.

PWR-ON/OFF is pin #59.

FWIW, I recently helped someone repair a TV using a different MSD SoC. In that case the problem was a bad 24MHz crystal. The symptom was similar.

Edit: I think U700 may be a class-D audio power amp, not a switchmode supply. Sorry for the error.

[krygods]

Re: Hitachi LE49S508

hey no worries bud, not time wasted on this side. I'm learning more and more so I'm appreciative of the help even if we did do a little extra work in the end. I'll make a few offers on ebay for a main board I saw a few on there the other day.

On to the next TV.

[krygods]

Re: Hitachi LE49S508

fzabkar thanks for the info, i'll check into that when I have some free time. going to have to do a little research to fully understand all the info you provided.

[fzabkar]

Re: Hitachi LE49S508

I'm a little confused about the LEDs. The voltages of the two LEDs are in opposite states (3.3V and 0V), so one should be on and the other off. However, my understanding is that neither LED is on. ???

I'm also trying to understand which voltages are switched on/off by PS-O/F and PB-O/F.

Does PS-O/F control the 120VDC supply for the boost converter, and does PB-O/F control the booster itself? If so, does it make any sense for one to be on while the other is off? Wouldn't both need to be on in run mode and both need to be off in standby?

[CapLeaker]

Re: Hitachi LE49S508

Alright, back lights come on now, no standby light. Power at LED+1 is 204VDC. So we've narrowed it down to a faulty main board then?

Yep, like I said earlier... however, it is always good to force on the PSU and check things, before you are spending new $$$ into a set.
budm helps so many folks out in here, it's easy to forget a small detail specifically if bits and pieces of crucial info is spread over pages.

[budm]

Re: Hitachi LE49S508

"Does PS-O/F control the 120VDC supply for the boost converter, and does PB-O/F control the booster itself? "
PS-ON is used for turning on the rest of the power supply, IE, PFC Voltage booster circuit, the switched 12V, etc.
The BL-ON is used to turn on the LED driver circuit, in this case it is used to turn on the switched transistor to supply the 12V to run the boost converter/LED controller IC (The LED power supply needs boosted Voltage to work).
the LED power supply puts out about 120VDC and that gets boosted again to over 200VDC for driving the LEDs