Toshiba 32AV502R

[Oznog]

Just got a Toshiba 32AV502R. The prior owner said it "used to take a long time to turn on, then it stopped turning on."

The power LED turns on and stays solid-on after I plug it in and press the power button on the side panel or the remote. But nothing else happens. There's no backlight and it doesn't look like the LCD is displaying underneath.

Jumped right in. The 24v, 12v, and 5v supplies are good and stable.

INV is 0.010VDC (apparently the mainboard doesn't want to turn on the backlight yet)
DIM in 0.064VDC.
PWR is 3.63VDC. (is this correct?)
ACD is 0.63VDC. (is this correct?)

I removed the connectors to the backlight & mainboard and powered the supply by itself.

5v is good, 12v and 24v are dead (expected).
ACD is 5.06v.
PWR is 0v.

I wondered why ACD was low when the board was attached (I don't know the way ACD is supposed to work). I see ACD is running through a 3.9K resistor on the power supply board. I unplugged the 110v and plugged the 2 board cons back in and powered it back up. There's 5v on the power supply board on the other side of that 3.9k resistor, so the mainboard is loading that one down to nearly 0v. It's not low because a signal found a problem in the power supply, because there's the same 5v on the other side of that resistor. The voltage has to be low because of current draw by the mainboard.

However... the PWR pin is still giving out power, apparently as as result of the mainboard. Is 3.63VDC correct for the PWR pin?

[budm]

Re: Toshiba 32AV502R

Can you upload good clear pictures of all the board and all the printing on the connector so we can see what the labels are? I would especially like to see the connectors on the inverter board. Also the model number of the LCD panel.
There are more than one version of this TV model.
http://www.shopjimmy.com/catalogsear...shiba+32AV502R

[Oznog]

Re: Toshiba 32AV502R

OK I see here someone posted a mfg's service brief:
https://www.badcaps.net/forum/showthread.php?t=23028

It says ACD shoud be 0.07v OUT of the supply board, and PWR is 2.4v INTO the supply board.

My first impression was that may be "close enough", but under more troubleshooting:
"Does a 2.4 volt on off signal appear at pin 13 of CN8 when the on/off button is pressed?"
NO-> "Is the Power Good (AC Detect) level less than .07V at pin 14 of CN8 when AC is applied?"

Well yeah it's less than 0.07v, not by a lot, but it IS less than 0.07v, which leads to "Suspect a problem with the SYSCON circuit located on the Main module."

Well great. but I was hoping for a simple power supply prob, I don't see anything about a SYSCON circuit.

[Oznog]

Re: Toshiba 32AV502R

Can you see this album?
https://www.badcaps.net/forum/album.php?albumid=77

[Oznog]

Re: Toshiba 32AV502R

I went to the mainboard and tried chilling all the caps with freeze spray. Tried chilling the whole board. No change.

Tried heating the whole board with a hair dryer. No change.

Hmm, didn't note this before, probably doesn't matter- the green power LED lights once for under 1 sec when I plug it in. When I press the POWER button, it lights solid and stays lit- curiously, pressing the POWER button again won't turn it off.

I did find another Toshiba manual:
ftp://remote.bobbyjonesinc.com/TOSHI...V/COMPLETE.pdf

Which has the exact model in the middle of the file (the pg numbers are wonky), the chart's the same though- PWR and ACD are out-of-spec.

[retiredcaps]

Re: Toshiba 32AV502R

In post #1, you wrote that ACD had 0.63V. As in 630mV. Is that a typo? Did you mean 0.063V or 63mV.

The flowchart says less than 0.07V or 70mV.

[Oznog]

Re: Toshiba 32AV502R

I meant 0.063v. I just read 0.055v a few sec ago.

There is a 3.3v regulator on the mainboard. That part is working correctly.

Looking through the little vent holes in the silver shielding box on the mainboard, I spied a 1.8v regulator inside there! However, it's also working correctly, darn it.

[Oznog]

Re: Toshiba 32AV502R

I see there's some "STA40T VTV-L4008" boards (same as mine) on eBay, but they mention being for 26", 37", or 40" AV502R TV's, and mine is a 32". Would it work or is the difference in screen size going to be a problem? Doesn't seem like it would be, the resolution and aspect ratio are the same, and the TCON board is what handles driving the LCD itself.

[budm]

Re: Toshiba 32AV502R

Never mind about the picture of the inverter board, Ifound the pinout of the connector.

[tom66]

Re: Toshiba 32AV502R

I've fixed a Toshiba 32WLT66S with an intermittent, slow to power up symptom. On the HDMI board, a 2.5V switching regulator had failed, giving about 0.1V out. I connected an LM317T linear regulator in its place (with heatsink) regulating from 5V and it powered right up, no problems.

[budm]

Re: Toshiba 32AV502R

Too bad the link to the service manual does not have the SCH for the boards.

[Oznog]

Re: Toshiba 32AV502R

I've fixed a Toshiba 32WLT66S with an intermittent, slow to power up symptom. On the HDMI board, a 2.5V switching regulator had failed, giving about 0.1V out. I connected an LM317T linear regulator in its place (with heatsink) regulating from 5V and it powered right up, no problems.

Well I wonder where we get 2.4v from here, the service info says the control board (mainboard) is what sources the 2.4v. I see the 3.3v and 1.8v linear regs.

2.4v is an uncommon voltage to actually use, the source is a mystery, and if you actually had 2.4v Vdd chips and a flaky reg passed 3.63v then you'll probably cause latchup and burn up the chip. Nothing's burned.

There MIGHT be another reg under the metal shield. I *barely* spotted the 1.8v reg under there.

[Oznog]

Re: Toshiba 32AV502R

Found more regs!

On the other side of the control board are two labeled "1117", that's a reg #.

They're U19 and U20, both TO-263. U19 is labeled:
"APL117
WL43U"
And has "weird" voltages (below)

U20 is near that, labeled:
"1117
-50PE"
and is 5.00v. So, "good".

There IS another reg under the shield! SOT223 U26:
"APL1117
BL62M18"
And it measured 1.8v Vout. Well it's got "18" in the part # so that's conclusive, although it's strange because there's a larger TO-263 reg putting out 1.8v under the shield that I saw before (that's U28, BTW).

U19 is "unusual", in that the pins are 1: GND/ADJ, 2(tab):Vout 3:Vin
And these measure 1: 7.8v 2(tab): 9.06v, 3: 11.91v.
I assume since there's no "4.3v" version of this part, that's not a voltage code, and thus this the adjustable version of the reg, the datasheet specifies "adjustable: no voltage code". The adjustable version's normal operating mode is 1.25v between Vout and ADJ, and 9.06v-7.8v=1.26v. And 9v is not an oddball value, either. NORMAL.

So despite the discovery of 3 additional regs, I don't actually have anything new to go on.

[Oznog]

Re: Toshiba 32AV502R

I found an APW7080 380KHz switching reg. It's got FB=0.8v which is what the datasheet says is normal operation, and the total Vout is 1.130v. The two divider resistors are labeled 622(6.2Kohm) high, 18C(15Kohm) low, which calcs to a target of 1.131v so that's correct.

[Oznog]

Re: Toshiba 32AV502R

Too bad the link to the service manual does not have the SCH for the boards.

Well what gets me is there's a flowchart here ending in "5 volt supply on the power supply module", "power supply module", "main module", and "SYSCON circuit located on the Main module".

Now that last one sure could use some explanation... and it's the one I need, apparently. Well narrowing it down to the mainboard is very helpful, but WTF is the "SYSCON circuit"??? It wouldn't seem to be worth mentioning if it were unrepairable and simply required replacement of the mainboard.

[randtek]

Re: Toshiba 32AV502R

Syscon is short for "System Control". It is just part of the main board. That information is just listed to help in diagnosing the bad board. Manufacturers no longer expect/intend for you to repair to the component level, and so their troubleshooting information is written to diagnose at board level. Schematics provided for today's TVs are grossly inadequate for diagnosing to component level, because they are not intended for that purpose.

[tom66]

Re: Toshiba 32AV502R

I expect this is mostly due to labour rates for TV repairs being so high, out of necessity due to the complexity of doing component level repairs. I try to do as many component level repairs as possible though.