Toshiba 32AV500U picture but no backlight

[retiredcaps]

Re: Toshiba 32AV500U picture but no backlight

I can't quite tell from the photos, but see if you can identify the secondary pins on the inverter transformer and see if they are within 3% of each other.

You are looking for something like this

http://www.lcdparts.net/TransformerD...ProductID=3494

[TechShui]

Re: Toshiba 32AV500U picture but no backlight

DakotaKid,

I'm working on a 42AV500U with the same exact problem.

The only difference being I haven't replaced the chips yet, because I'm considering replacing the whole board instead... I have a question: When you test resistance on the mosfets what are your readings?

My master inverter seems OK, all four mosfets give the same reading, 1.1Mega Ohms on the left leg of each FET, with 0 Ohms on the right leg of each.

The slave is a different story:
6k Ohms on left leg of Q205,
51.3k Ohms on left of Q206. (both have 0 Ohms on the right).
The remaining two mosfets on the slave board seem consistent with the master's readings (1.1M Ohms / 0 Ohms)

[DakotaKid]

Re: Toshiba 32AV500U picture but no backlight

My master FETs all ohmed out at around 1.3M Ohms from both legs and the slave Q205 and Q206 did as well. The left hand FETs on the slave board ohmed out at 0 so they were shorted. I am going to test my 9897 IC. I still have two brand new 9897 IC's to use if necessary. If you aren't comfortable replacing/soldering the SMD 9897 IC then I'd recommend replacing the entire board. I could be wrong but those readings on your master FETs don't seem good, you sure they aren't shorted?

Regarding testing the backlight...The backlight doesn't seem to show any distinct pattern when it comes one, maybe a bit dim though if anything. After pressing the power button the backlight flashes quickly once then off a couple of seconds then back on for about a second or two then goes off. The green power light stays on throughout and after all of this occurs.

Also...the voltage at the input to the transformers is about 5.5V when the TV is on but backlights are off after they fail to stay lit. If I measure that voltage as I turn the TV on it spikes briefly when the lights comes on before dropping back to 5.5V after the backlight fails.

I have attached inverter schematics that seem to be the same boards though these are labelled 812 instead of 813.

[budm]

Re: Toshiba 32AV500U picture but no backlight

Hi DakotaKid, do you have the service manual for this TV? I have been trying to get the diagram of the master/slave inverter circuits to see how they work in pair. Can you provide the link? Thanks.
By the way, when MOSFET shorted out, it can take out the output drive circuits inside the IC with it.

[DakotaKid]

Re: Toshiba 32AV500U picture but no backlight

I found a couple of different versions of the SM for this TV at elektrotanya but none include any schematics or diagrams of the inverters, only the interconnect block diagrams for the boards. It also does not include the interconnect between the master and slave. The schematics I attached for 812 M & S are the closest I have found.

[budm]

Re: Toshiba 32AV500U picture but no backlight

Do you have the Master in PDF?

[DakotaKid]

Re: Toshiba 32AV500U picture but no backlight

Do you have the Master in PDF?

attached as pdf. Hope this helps.

[DakotaKid]

Re: Toshiba 32AV500U picture but no backlight

Here is the transformer. I haven't yet figured out which pins are P and which are S.

[budm]

Re: Toshiba 32AV500U picture but no backlight

As you can see from the schematic, there are only 2 windings on the transformer. so you should be able to read the resistance on each windings, for example, the one on the bottom of the picture, on the right side you can see copper wires from the bobbin to the terminals.
Usually the high voltage side will have resistance of 500 Ohms and higher.

[DakotaKid]

Re: Toshiba 32AV500U picture but no backlight

Here is the updated picture of the transformer. Resistance measures .1 Ohms across the primary, 23.2 Ohms across the secondary high voltage side.

[retiredcaps]

Re: Toshiba 32AV500U picture but no backlight

Here is the updated picture of the transformer. Resistance measures .1 Ohms across the primary, 23.2 Ohms across the secondary high voltage side.

Try brute force way below. 23.2 ohms is way too low for a secondary resistance reading.

https://www.badcaps.net/forum/showpo...6&postcount=20

[TechShui]

Re: Toshiba 32AV500U picture but no backlight

My master FETs all ohmed out at around 1.3M Ohms from both legs and the slave Q205 and Q206 did as well. The left hand FETs on the slave board ohmed out at 0 so they were shorted. I am going to test my 9897 IC. I still have two brand new 9897 IC's to use if necessary. If you aren't comfortable replacing/soldering the SMD 9897 IC then I'd recommend replacing the entire board. I could be wrong but those readings on your master FETs don't seem good, you sure they aren't shorted?

Regarding testing the backlight...The backlight doesn't seem to show any distinct pattern when it comes one, maybe a bit dim though if anything. After pressing the power button the backlight flashes quickly once then off a couple of seconds then back on for about a second or two then goes off. The green power light stays on throughout and after all of this occurs.

Also...the voltage at the input to the transformers is about 5.5V when the TV is on but backlights are off after they fail to stay lit. If I measure that voltage as I turn the TV on it spikes briefly when the lights comes on before dropping back to 5.5V after the backlight fails.

I have attached inverter schematics that seem to be the same boards though these are labelled 812 instead of 813.

The two MOSFETs (Q205/Q206) on the left on my slave inverter are the ones that were shorted. In other words the same as your findings.

This seems to be a common issue, there's even Coppell repair kits on eBay that have the controller IC and five MOSFETS.


People are gouging the prices of the inverters, because they know they're in high demand

By the way, my TV is also a Regza 32AV500U, but the inverters are HIU-811

[DakotaKid]

Re: Toshiba 32AV500U picture but no backlight

Try brute force way below. 23.2 ohms is way too low for a secondary resistance reading.

https://www.badcaps.net/forum/showpo...6&postcount=20

I would be interested in seeing what others get when they test their transformers for resistance. I get 1300K Ohm from P->S pins but continue to get about 23 Ohms on both the master and slave transformers between S1 and S2. The brute force method yielded nothing different. This is a very straightforward two coil transformer so there aren't many different ways to check it. The other odd thing that I've seen on mine and all pictures of these boards is a whitish color residue that looks almost like a scorch mark around each of the middle transformer pins. Every time I search for any info on this TV I find info about this inverter problem and comments around the microfuse, FETs, control IC, two large caps, and (sometimes) transformers having been replaced. I am beginning to wonder if the entire circuit is so poorly engineered or built with inferior parts such that it blows everything from the fuse thru the IC, caps, FETs, and transformer. I have yet to read about many successful repairs of this TV / inverters. It also most likely explains why Toshiba changed to a re-engineered single inverter board mid production stream of this TV. Sorry but my patience is wearing thin. I know the answer is there but it sure is elusive.
DK

[electronicsurplus]

Re: Toshiba 32AV500U picture but no backlight

Sorry, I hope I am not hijacking this message or whatever it is called

I have a pdf a copy of the service manual for that television

A copy is also available on Tom's site, just uploaded


Jon
Electronic Surplus Recyclers LLC

Do you have the Master in PDF?

[electronicsurplus]

Re: Toshiba 32AV500U picture but no backlight

The Service manual is also available @

[retiredcaps]

Re: Toshiba 32AV500U picture but no backlight

I get 1300K Ohm from P->S pins but continue to get about 23 Ohms on both the master and slave transformers between S1 and S2.

The inverter transformer I pointed to in post #21 is only an example of what to look for. That is, the pins may vary as to which is the primary and secondary. 1300 ohms or 1.3K ohms sounds about right. You listed 1300K ohms, is that a typo?

If inverter transformer measure 1300 ohms on each board, then they are likely okay.

[DakotaKid]

Re: Toshiba 32AV500U picture but no backlight

Sorry, I hope I am not hijacking this message or whatever it is called. I have a pdf a copy of the service manual for that television

No worries. I have the SM pdf but the problem is that it doesn't have details for the inverter boards, only the connecting plug voltages. I posted board schematics for the inverters in an earlier post but it doesn't list capacitor values or expected voltages at test points. Since we are pretty certain that these TVs are failing due to the inverters and have found failed components on the inverter boards it is that detail that is needed. But, thanks for the info.

The inverter transformer I pointed to in post #21 is only an example of what to look for. That is, the pins may vary as to which is the primary and secondary. 1300 ohms or 1.3K ohms sounds about right. You listed 1300K ohms, is that a typo?

If inverter transformer measure 1300 ohms on each board, then they are likely okay.

It really is 1300K but that is measured across the Primary pins to Secondary pins. Across S1 and S2 measures 23 Ohms which leads me to believe the transformers are possibly bad which might in turn put the backlight into shutdown mode. Last night I measured the voltage at all pins on all IC's on both inverters. I will post that here when I can put it in a readable format. There is definitely a "screaming/hissing" noise coming from the Slave board transformer when the backlights briefly fire up. Unfortunately, the length of time that the backlight stays on is so brief that it's about impossible to get voltage readings except when it has already shut down.

DK

[budm]

Re: Toshiba 32AV500U picture but no backlight

Since the Master and Slave use the same transformers, I would swap them and see if the noise follows, you already replaced the IC and the MOSFET's on the Slave board already, right?

[TechShui]

Re: Toshiba 32AV500U picture but no backlight

...I will post that here when I can put it in a readable format. There is definitely a "screaming/hissing" noise coming from the Slave board transformer when the backlights briefly fire up. Unfortunately, the length of time that the backlight stays on is so brief that it's about impossible to get voltage readings except when it has already shut down.

DK

That's why you need a second person to press the power switch while you have the probes in place. Either that, or tape the black probe to the chassis (GND) of the TV, that way you can use one hand for the red probe, and your other hand free for the power switch.

I posted board schematics for the inverters in an earlier post but it doesn't list capacitor values or expected voltages at test points. Since we are pretty certain that these TVs are failing due to the inverters and have found failed components on the inverter boards it is that detail that is needed.

Umm, aren't the capacitor values marked on there? Did you mean these, in your photo > https://www.badcaps.net/forum/showthread.php?t=20371#3

Those two caps have 24V going thru them. Even if you're referring to some other capacitor, chances are good that it's also on the 24V rail, you can trace the circuit visually to make sure.

[retiredcaps]

Re: Toshiba 32AV500U picture but no backlight

That's why you need a second person to press the power switch while you have the probes in place. Either that, or tape the black probe to the chassis (GND) of the TV, that way you can use one hand for the red probe, and your other hand free for the power switch.

A good multimeter with aligator clips and min/max will capture the reading.