LN32C450E1DXZA Main board fixes?

[ngth82]

Re: LN32C450E1DXZA Main board fixes?

I ended up parting the TV out. A new (to me) main board goes for $60+ dollars. The ROI on this 32" unit just isn't there.

I left the panel running for several hours with the power/main board cable disconnected. This automatically forces the CCFL backlights on. They didn't turn off at all. Main board is highly suspect.

It just wasn't worth the investment and i got a scrap metal picker to pick up 4 TV's and 7 TV stands... time to cut the clutter.

Thanks for the help though!

Thread closed.

[ngth82]

Re: LN32C450E1DXZA Main board fixes?

Hey Budm, yeah that seems to be fairly elusive. I'll keep digging though.

Maybe i'll come across a LN32C450 with a broken LCD and i can swap parts into it.

[budm]

Re: LN32C450E1DXZA Main board fixes?

I have not found any schematic for the main board or even the block diagram to show what signals it wants for the main board to operate.

[ngth82]

Re: LN32C450E1DXZA Main board fixes?

I looked at this some more. But i haven't been able to gain much additional insight (really haven't had much time either).

I'm currently in search of the inverter board schematics for this Chi Mei V315B5-L06 panel, but I haven't been able to find it. I'm currently curious if one or more of the lamps is reaching end of life and is faulting, then in turn the main board shuts it off.

As i said previously, if the cable between the MAIN and PSU is connected, the lamps would stay on. So it could be a possibility. I want to see how the fault signal (5V_DET) is hooked up on the inverter.

The power board is a BN44-00338B (attached). Page 2 shows CN803, pin 4. On the power board silk screen, that is marked 5V_DET. In the schematic it is "INV_ERROR". This is pulled up by default. According to the panel spec sheet, the normal state of this pin is low when the inverter is operating correctly.

On the power board, INV_ERROR is routed to the base of the QT853 NPN. The collector sits at about 5.4V. The emitter is connected to GND. The collector is connected to CN802, pin 2 which goes to the main board.

• When INV_ERROR (CN803, pin 4) is high, QT853 is "ON" and pulls 5V_DET at CN802, Pin 2 low.
• When INV_ERROR (CN803, pin 4) is low, QT853 is "OFF" and 5V_DET at CN802, Pin 2 high.

Previously (Post #10), I pulled INV_ERROR low through a 100 ohm to GND and it didn't make any difference. Interesting data point. If the INV_ERROR pin is satisifed (e.g. no error condition), then the main board should have stayed on..

This looks like it's pointing back to a bad main board.

PS, looks like the pin i was calling "HSVON" was "H-SYNC" (not used on the power board CN802.8 connector).

[ngth82]

Re: LN32C450E1DXZA Main board fixes?

Good morning Budm -

Correct, the service manual that i have doesn't have the board schematics for the main, inverter or SMPS. The link that you provided are all the items i've downloaded before, but no schematics are in them.

I was not able to find a direct hit for a LN32E450E1 on my standard go-to sites: elektrotanya.com, eserviceinfo.com or toms-service-manuals.com

Cosmetically, this unit is in really good shape. ... I'll keep on looking.

[budm]

Re: LN32C450E1DXZA Main board fixes?

I did not look at your service manual yet, so the one you have does not have the schematic for the main board?
Did you try elektrotanya?
https://elektrotanya.com/showresult?...oria=&kat2=all

[ngth82]

Re: LN32C450E1DXZA Main board fixes?

That 5V_DET (normally LOW) output of the inveter board is being converted to HIGH to satisfy the the main board (main board is looking for HIGH for normal condition), if there is true inverter error then the backlights will not come on and stay on.
At this point it is the matter of troubleshooting the main board to find out why PS-ON is turned off.

Hi budm, do you have any good leads on the main board schematic? I have not been able to find one. Thank you!

I’m going to turn in. More tv debug Sunday.

[budm]

Re: LN32C450E1DXZA Main board fixes?

That 5V_DET (normally LOW) output of the inveter board is being converted to HIGH to satisfy the the main board (main board is looking for HIGH for normal condition), if there is true inverter error then the backlights will not come on and stay on.
At this point it is the matter of troubleshooting the main board to find out why PS-ON is turned off.

[ngth82]

Re: LN32C450E1DXZA Main board fixes?

Yeah, that's what i would expect as well, however that doesn't appear to be the case.

This is what i did:
The 5V_DET signal goes between the power board and the inverter board (see the overall pic in POST #4). I disconnected the 5V_DET signal on the inverter board side (just slid the pin out from the plastic connector body). I tied it to GND through a 100 ohm resistor. I thought this would take care of it. 5V_DET on the PSU to MAIN board side STILL rises up to 5V before decaying. In the service manual, this is listed as INV_ERROR.

I thought 5V_DET was routed straight through from connector CN803 (inverter side) to CN802 (main board side). But that is not the case. It goes through a NPN inverter circuit implementation. Please see the attached PIC.

To my understanding, when INV_ERROR is HIGH, the NPN QM852 turns on, thus pulling 5V_DET LOW.
When INV_ERROR is LOW, QM852 is OFFso it should sit around ~5V.

Right now, i have INV_ERROR LOW; so 5V_DET is HIGH to the main board, but the behavior doesn't change at all. I still see the backlights flicker a few times and the PS_ON signal is short (370ms)

[budm]

Re: LN32C450E1DXZA Main board fixes?

Hi Budm -
(Interestingly enough, you've attempted to help another member or two on this forum with this EXACT tv).

I found the panel spec - CHI MEI - V315B5-L06 -
Section 3.2.3 shows DET_5V = high (4.5V to 5.5V) is the abnormal state. 0V to 0.8V is the normal state.


I guess this may point to an error in the panel inverter board.

If that is the case then when you pull that pin low then the PS-ON should stay present.
But you also indicated that you are able to get the backlights to come on and stay on.

[budm]

Re: LN32C450E1DXZA Main board fixes?

So those signals may not be the cause of the problem then.
I did not download the service manual to study it yet.

[ngth82]

Re: LN32C450E1DXZA Main board fixes?

Hi Budm -
(Interestingly enough, you've attempted to help another member or two on this forum with this EXACT tv).

I found the panel spec - CHI MEI - V315B5-L06 -
Section 3.2.3 shows DET_5V = high (4.5V to 5.5V) is the abnormal state. 0V to 0.8V is the normal state.


I guess this may point to an error in the panel inverter board.

[ngth82]

Re: LN32C450E1DXZA Main board fixes?

Hi Budm -

without modification, both HSVON and 5V_DET both go high when i push the power button. (PIC4 and PIC1, respectively)

Here's the result of your ask. Signals were pulled high to A5V/low to GND through a 100ohm series R:

5V_DET=low, HSVON=low ==> no behavior change
5V_DET=low, HSVON=high==> no behavior change
5V_DET=high, HSVON=low ==> no change (per comment above)
5V_DET=high, HSVON=high ==> no change (per comment above)

[budm]

Re: LN32C450E1DXZA Main board fixes?

"A5V IS PRESENT and reads ~5V." That is what I expected.
The PS-ON may have been force off due to error signals.
You can try by disconnecting those two error signal pins and then try pulling them high or low combination using 1K on each pin connected between A5V and the pins on the main board side to see what will happen, to pull low you just GND it through 100 Ohms resistors.
You will have 4 combinations to do:
HIGH HIGH
LOW LOW
HIGH LOW
LOW HIGH

[ngth82]

Re: LN32C450E1DXZA Main board fixes?

Post #4 and Post #6 have incorrect information about A5V. A5V IS PRESENT and reads ~5V.

I had the scope set on an edge trigger from a single sequence. Since A5V is always on, i won't see a rising edge on the scope when i turn the unit on via the power button. The next thing to do is try and figure out why it shuts down ~370ms after issuing PS_ON.

A5V is present.

Re post #7 - it does not appear to have a temperature dependency. Heating/cooling the board doesn't change the TV behavior.

[budm]

Re: LN32C450E1DXZA Main board fixes?

BTW, Does heating and cooling the board have any affect?

[ngth82]

Re: LN32C450E1DXZA Main board fixes?

Hey Budm -

Thanks for chiming in. I'm always appreciative of your input.

The service manual is attached.

I'll look in to A5V..
Yes, PS-ON comes up to ~0.7V then turns off ~370ms later. Please see "PIC6 -PS_ON.jpg" in post #4

I did not see anything regards to HVSON/5V_DET in the service manual

[budm]

Re: LN32C450E1DXZA Main board fixes?

A5V is the the Standby 5V so it should be present ans steady at 5V.
B5V and B13V are switched power supplies that will be turned on when the PS-ON is present.
So does the PS-ON signal come up to around 0.7V and then drops down to 0V?
Some of PS-ON signal can be as low as 0.7V just enough to bias on the switched Transistor to turn on the Opto to turn on the PFC and the rest of the power supplies.
The 5V_DET and the HVSON look to be error signals, I do not know if it is active HIGH or ACTIVE LOW, but since you have service manual, what does it say about thses two signals?
May be you should upload the service manual.

[ngth82]

Re: LN32C450E1DXZA Main board fixes?

I have a few updates to provide. I spent a little bit of time with my old 100MHz scope and poked around the ribbon cable between the power and main boards.

Pics of the boards are attached.

The connector pinout is shown in Pic0.

PIC1 shows 5V_DET active for ~360ms before turning off. It's a single shot.
PIC2 shows BLU_ON active for ~370ms before turning off.
PIC3 shows the initial charge and decay of E-PWM
PIC4 shows HSVON(?) - ~380ms
PIC5 shows B5V - 5V@ ~370ms
PIC6 shows PS-ON - ~325ms, the voltage level is ~734mV.
PIC7 shows B5V (in column 1) - 5V, 370ms
PIC8 shows B13V - measured out to be 12.6mV peak with my DMM. ~370ms



Note 1: There is another 5V pin on the connector pin out that is called A5V, but i don't see it rise on the scope, even with the trigger level low. The service manual has a diagnostics flow chart box that references A5V.... I'll investigate this one.

Note 2: The PS-ON signal initially seemed a bit low to me. But i measured the PS-ON pin on the Power supply with the cable between the PSU and the main board disconnected. It shows ~734mV (and interestingly enough, thats enough bias to turn the backlights on).


~350-380ms after the PSon signal is asserted, it turns itself off. Time to chase why that part is happening. The fault seems to be on the main board not being satisfied during start up.

[ngth82]

Re: LN32C450E1DXZA Main board fixes?

Hey #freakaftr8, thanks for the reply.

No audio, no picture with the usual poking around with a flash light.

If i look at the main board, the optical audio out doesn't appear to be "on" either (no red glow from the output).

With the main board connected, pushing the power button would result in the high voltage transformer turning on a few times, as noted by the flickering of the CCFL tubes, then it would stop.

The backlights work with the main board *disconnected*.

The PS-ON signal does not remain high when you have the main + power boards connected to each other.