Sylvania LC420SS8 shutting down on protect(?)

[iKitsune]

Re: Sylvania LC420SS8 shutting down on protect(?)

I just look at the board layout on page 48, I can see jumpers (protect 2) J134, 135 that go over to the right side of the board and connected to D801 and D228 which are not shown in the diagram, are those section of the board stuffed with parts?

No, that section of the board is pretty sparse, and neither of those points is populated.

[budm]

Re: Sylvania LC420SS8 shutting down on protect(?)

That is way too low, you can see that it has 100K (R3117) resistor between the protect pins (64) and ground. You are testing it with the TV unplug?
It can be bad MLCC (MULTI-LAYER-CERAMIC-CAP) C1111 (1000pF) that is connected on pin 64.
Oh by the way, what do you read on the Anode side of that Diode?
I think we are getting close.

[iKitsune]

Re: Sylvania LC420SS8 shutting down on protect(?)

That is way too low, you can see that it has 100K (R3117) resistor between the protect pins (64) and ground. You are testing it with the TV unplug?

Yes, the set is unplugged when I'm doing resistance testing. The measurement was between pin 64 of the IC and the frame ground.

[budm]

Re: Sylvania LC420SS8 shutting down on protect(?)

I suspect bad c1111 or worst case, internal short in the IC. I would try removing the cap.
Something is really loading down this line.

[budm]

Re: Sylvania LC420SS8 shutting down on protect(?)

Another interesting find on this model.
https://www.badcaps.net/forum/showth...SS8#post253049

[iKitsune]

Re: Sylvania LC420SS8 shutting down on protect(?)

I suspect bad c1111 or worst case, internal short in the IC. I would try removing the cap.
Something is really loading down this line.

Wellp, I'm retarded. My meter had a dead battery, so all the resistance values are out the window. Retest with a fresh battery: 99.34 kOhm.

[iKitsune]

Re: Sylvania LC420SS8 shutting down on protect(?)

Another interesting find on this model.
https://www.badcaps.net/forum/showth...SS8#post253049

Removed D655 per the service bulletin, and there was no change to the set.

[budm]

Re: Sylvania LC420SS8 shutting down on protect(?)

That is just for the buzzing problem, not relate to what you are working on, I just point that out for FYI.
So you need to check to check the DC reading again then on Portect 1,2,3,5,6.

[iKitsune]

Re: Sylvania LC420SS8 shutting down on protect(?)

That is just for the buzzing problem, not relate to what you are working on, I just point that out for FYI.
So you need to check to check the DC reading again then on Portect 1,2,3,5,6.

Ugh, my laptop battery runs out at the worst time, sorry for the long delay on response. My remark about the diode removal wasn't that I expected it to fix it, I'm just documenting *everything* I do to this unit.

I comprehensively rechecked all the voltages I'd measured yesterday.

PROTECT1: 2.57
PROTECT2: 0.88
PROTECT3: 2.97
(spent half an hour looking for protect4, lol)
PROTECT5: 3.25
PROTECT6: 2.99
VT+33v: 31.8
LCD+12v: 11.99
+6v: 7.28
+2.7v: 2.17
AL+3.3v: 3.19
P-ON+6v: 5.48
P-ON+9v: 8.84
+3v: 3.07
+4v: 3.87
+24v: 23.1

I was looking at the schematic again, and on page 33, the voltage chart for CN201 says PROTECT2 should be 0.9v, which is pretty close to what I'm reading.

[budm]

Re: Sylvania LC420SS8 shutting down on protect(?)

OK, it looks like we ned to look at the Protect 3 (24v present detection), you can lift one end of the detector diode D757 and see if you will still get error condition, it the error is gone then we can concentrate on the 24v power supply circuits next.

[iKitsune]

Re: Sylvania LC420SS8 shutting down on protect(?)

OK, it looks like we ned to look at the Protect 3 (24v present detection), you can lift one end of the detector diode D757 and see if you will still get error condition, it the error is gone then we can concentrate on the 24v power supply circuits next.

Fault remains with D757 lifted.

[budm]

Re: Sylvania LC420SS8 shutting down on protect(?)

So it still flashing the code? So far I do not see any info on the flashing error code in the service manual. Something else is triggering the error some where. I hope it is not corrupted EEPROM problem.

[iKitsune]

Re: Sylvania LC420SS8 shutting down on protect(?)

So it still flashing the code? So far I do not see any info on the flashing error code in the service manual. Something else is triggering the error some where.

Yeah it's still flashing, but it's a constant fast flash, not a code. I don't see codes either, and that's why I feel like I'm missing something obvious. Right now my thought is one of the control ICs on the mainboard, sadly. The voltages coming off the power section all look good.

Opinion time: If it is the mainboard (and assume I'm not set up to do PQFP or BGA rework), would this set be worth putting an eBay / ShopJimmy mainboard in, or should I just haunt Craigslist and look for one someone smashed the LCD on? Looks like a mainboard on ShopJimmy is around $135.

[iKitsune]

Re: Sylvania LC420SS8 shutting down on protect(?)

As an aside, I've already tried "obvious" things, like separating the T-con from the digital board, and separating the panel from the T-con with the T-con still connected to the digital board, to see if that changed the fault.

[budm]

Re: Sylvania LC420SS8 shutting down on protect(?)

Not sure either for 42" TV to be worht it or not.

[iKitsune]

Re: Sylvania LC420SS8 shutting down on protect(?)

Not sure either for 42" TV to be worht it or not.

I've got an idea involving IC3101 I'm going to try later, though. It's a Renasas uC I'm somewhat familiar with, I think it might have a problem.

[iKitsune]

Re: Sylvania LC420SS8 shutting down on protect(?)

Or one of the inputs to it does. Something coming across the power board from CN202 could be forcing it down; disconnecting CN202 (which only carries audio and a couple control signals) changes the behavior - the only thing so far that has! The unit blinks 3 times and then promptly shuts down instead of sitting there for 10 seconds blinking and trying to start up. For as lovely as this service manual is, a list of blink codes would help me out.

Edit: Durp, bet it's PROTECT3.
Edit edit: PROTECT6, I can't read. That shoots down my theory of it being a PROTECT line triggering either way.
Edit edit edit: 10 seconds, not minutes.

[iKitsune]

Re: Sylvania LC420SS8 shutting down on protect(?)

So it still flashing the code? So far I do not see any info on the flashing error code in the service manual. Something else is triggering the error some where. I hope it is not corrupted EEPROM problem.

I'm back to thinking regulation; I accidentally bumped my thumb against the tab of the AL+3.3v regulator on the power board, and it was alarmingly hot. (IC220). Any thoughts on if this could be a regulation issue? The input feeding the 3.3v regulator was almost 20% high. Most of the voltages are right on the edge of being 10% out of spec, some are more.

[budm]

Re: Sylvania LC420SS8 shutting down on protect(?)

It should be too hot to touch, if you cannot leave the finger on it for mare tha 10 seconds, that will be hot. How high is the input voltage?

[iKitsune]

Re: Sylvania LC420SS8 shutting down on protect(?)

It should be too hot to touch, if you cannot leave the finger on it for mare tha 10 seconds, that will be hot. How high is the input voltage?

The schematic and the datasheet for the regulator say it should be 6.3v. I'm reading 7.2v.