This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

[Paul678]

.....Until he saw my Craig's ad for broken TVs........
His TV has sound, but no picture.

The repair kit on Ebay consists of both the Master and Slave
inverter boards:

http://www.ebay.com/itm/TOSHIBA-37AV...-/170554383879

And there apparently are substitute inverter boards:

http://blog.coppelltvrepair.com/2010...cement-in.html


The Ebay kit is about $100 with the shipping, so
that's a bit pricey, but isn't there a decent chance it's
only a blown fuse, like on the Sceptre I recently worked on?

And since he was about the throw the thing away
anyways, am I being an asshole to offer him $5??

[PlainBill]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

.....Until he saw my Craig's ad for broken TVs........
His TV has sound, but no picture.

The repair kit on Ebay consists of both the Master and Slave
inverter boards:

http://www.ebay.com/itm/TOSHIBA-37AV...-/170554383879

And there apparently are substitute inverter boards:

http://blog.coppelltvrepair.com/2010...cement-in.html


The Ebay kit is about $100 with the shipping, so
that's a bit pricey, but isn't there a decent chance it's
only a blown fuse, like on the Sceptre I recently worked on?

And since he was about the throw the thing away
anyways, am I being an asshole to offer him $5??

I'd give him a sawbuck, a double sawbuck if he includes the remote.

PlainBill

[tom66]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

And no need to replace both boards. Most likely just one is failed and if it's a transformer or MOSFET, that should be easy to locate.

[Paul678]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

And no need to replace both boards. Most likely just one is failed and if it's a transformer or MOSFET, that should be easy to locate.

Do you think there's a good chance I can repair
the bad inverter at the component level?

It looks like most people sell the Master and Slave
together, no separately, so that would be pricey.....

[tom66]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

Do you think there's a good chance I can repair
the bad inverter at the component level?

It looks like most people sell the Master and Slave
together, no separately, so that would be pricey.....

Yes, I'm pretty sure you could repair it yourself.

[Paul678]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

Ok, the fella gave it to me for free!

Cracked it open.....the main fuse on the power
supply is MISSING! I could have swore the fella
said no one has worked on this, but I'm not sure how
a fuse can dissappear.

The fuse is labeled T 4.0A H/250V.

Should this one be a fast or slow-blow?

Ceramic or glass, or it doesn't matter?\

And should I be looking for shorted out bridge rectifier diodes,
or shorted filtering caps?

[tom66]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

Ok, the fella gave it to me for free!

Cracked it open.....the main fuse on the power
supply is MISSING! I could have swore the fella
said no one has worked on this, but I'm not sure how
a fuse can dissappear.

The fuse is labeled T 4.0A H/250V.

Should this one be a fast or slow-blow?

Ceramic or glass, or it doesn't matter?\

And should I be looking for shorted out bridge rectifier diodes,
or shorted filtering caps?

Should be time delay. That's what the "T" indicates.

I bet the guy opened it up, took the fuse out and tested it (probably found it was okay) and forgot to put it back in or lost it and didn't know what to replace it with. But a free TV, can you complain?

Filter caps rarely short; but a simple check would be to replace the fuse (buy a pack of five or so.) If it blows straight away (this is a safe failure mode), you have a power supply problem, which is usually fairly simple to find. (Shorted MOSFET, shorted bridge rectifier, etc.)

[Paul678]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

Should be time delay. That's what the "T" indicates.

I bet the guy opened it up, took the fuse out and tested it (probably found it was okay) and forgot to put it back in or lost it and didn't know what to replace it with. But a free TV, can you complain?

Filter caps rarely short; but a simple check would be to replace the fuse (buy a pack of five or so.) If it blows straight away (this is a safe failure mode), you have a power supply problem, which is usually fairly simple to find. (Shorted MOSFET, shorted bridge rectifier, etc.)

SWEET! It's a shorted D4SB S6:



I'm trying not to get too excited here! But if it's
just this rectifier and a fuse, life would be swell!!!

[tom66]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

SWEET! It's a shorted D4SB S6:



I'm trying not to get too excited here! But if it's
just this rectifier and a fuse, life would be swell!!!

Nice. How did you determine the short? Could be a shorted MOSFET, for example, between the + and - pins.

Are you sure about that part? That's a 60V device. It would go pop on 115V mains which is 160V peak. Should be at least a 200V device, preferably 400V or 600V.

And I'm trying to figure out how you'd have sound but no picture with a shorted bridge rectifier and blown fuse.

[budm]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

You should diconnect all the load from the power supply first, yif you have shorted load, it could damage the new rectifiers, as TOM said, you have shorted loads.
You should use GFCI outlet when work on line powered products for safety.
http://s807.photobucket.com/albums/yy352/budm/Tools/
By the way, where uis this D4SB S6 is located?

[budm]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

I agree with Tom, per spec. this 60v bridge rating is not right at all, It should be 4~500v rating.

[Paul678]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

Nice. How did you determine the short? Could be a shorted MOSFET, for example, between the + and - pins.

Are you sure about that part? That's a 60V device. It would go pop on 115V mains which is 160V peak. Should be at least a 200V device, preferably 400V or 600V.

And I'm trying to figure out how you'd have sound but no picture with a shorted bridge rectifier and blown fuse.

I always verify shorts by removing the component completely
from the circuit. I've had a shorted filter cap past a voltage regulator, that
made the rectifier look shorted in-circuit, so I'm well aware of this.
The peak for 120V would be about 170V, so yeah, I'm thinking whoever removed the fuse, may have done some more dirty work, like installing incorrect parts (the pads on the bridge indeed looked sloppy)! Luckily, the lady at the parts counter gave me a KBU4J, which has a peak reverse voltage of 600V.

Yeah, I could have sworn he said he still had sound, but
clearly this wasn't the case.......

My optimism is fading......but I'll let you know what happens....

Thanks for the input....

[rpgruss]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

There are two rules about people getting rid of broken TVs.

1) If they tell you what's wrong, they are wrong or are lying
2) If they say it's an easy fix, they are lying

I've fixed 25 TVs and monitors, and only one time was the seller correct about the failure.

If the bridge rectifier shorted, don't be surprised if more things are broken upstream. I have an epic thread going here about fixing a power supply that blew it's rectifier, looking back every single fault can probably be traced to that. The damage so far is the standby controller, couple resistors, and possibly the power factor controller...

[Paul678]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

Ok, the power supply is fixed!

Totally screwed up that someone put in the WRONG
bridge rectifier! haha!

Ok, now all PS voltages are normal, remote control works,
and manual ON/OFF button works correctly....but still no
picture, even though healthy +24V is getting to both
inverters.

The Master:







The Slave:






All +24V pins are good. Plus:

DIM pin = +2.2V
INV pin = +5

And one signal is +0.7V on the 10 line
synchronizing ribbon, while all the rest
are 0 Volts.

I found only one +24V fuse on each
board, and they are both good. The +24V
gets sent to what I believe is the drains of
Q1 and Q5 (in third picture), but when I
try to measure an AC voltage on the
primary side of the transformers, I get
nothing. So apparently the switching
action is not there.

Any advice greatly apprectiated....

[rayrod81]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

It is most likely the driver IC on one of the inverters that has gone bad. Sometimes one (or more) of the FETs go bad as well. I had one of these exact TVs and the Slave had a bad driver IC but the FETs were good. $10 and one BD9897FS IC later the TV was working great. Check the resistance across the FETs on both the master and slave. If you find a short or low resistance reading then that will confirm the IC is bad and needs to be replaced. I believe you can find a repair kit with the IC and a couple of the FDD8447L FETs for around $15 or less depending on where you order from.

[tom66]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

Philips also released a repair kit for certain inverter boards to prevent the problem from occurring again. Might be compatible with this inverter?

[Paul678]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

It is most likely the driver IC on one of the inverters that has gone bad. Sometimes one (or more) of the FETs go bad as well. I had one of these exact TVs and the Slave had a bad driver IC but the FETs were good. $10 and one BD9897FS IC later the TV was working great. Check the resistance across the FETs on both the master and slave. If you find a short or low resistance reading then that will confirm the IC is bad and needs to be replaced. I believe you can find a repair kit with the IC and a couple of the FDD8447L FETs for around $15 or less depending on where you order from.

Thanks much, Rayrod. I found 2 bad FETs on the
slave board. I assume because of the synchronize
ribbon, if one IC or board doesn't work, then the other
will not turn on either, which is why I didn't see
any switching on either board, right?

Wow, it's as low as $3.80!

http://www.ebay.com/itm/1PCS-X-IC-RO...item3a71270002

But the ship time is too long from China to the USA, so I don't mind
paying $9 more:

http://www.ebay.com/itm/HIU-813-M-HI...item25602e5f3d

Coppell recommends here that you replace ALL 4 mosfets,
even the ones that test good.

The Slave IC chip looked bad to me, because even when I disconnected
the bad FETs, one of the gate pads had continuity to multiple pins.
On the Master board, each of the 4 gates went to one pin, which
looked normal.

Ok, the pitch on this chip isn't as bad as Plasma Y-sustain buffer
ICs, but they are still pretty small! How did you handle the
rework? Since I don't have a hot-air station, I'm probably
gonna cut all the leads at the chip, remove the chip, and then
remove each cut lead from the pads. Hopefully I don't tear
any pads off. I'll try to solder the new one in by hand....it
won't be easy. Professional solderers get your respect when
you try to do their job!

Worse comes to worse, I'll just buy this one:

http://www.ebay.com/itm/HIU-811-S-Ba...item2a1a21a78e

[randtek]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

For removing these ICs, you should order a product called "Chip-Quik". It is a "solder" alloy that has a very low melting point. You just add a bunch of it all around the chip, it dilutes the regular solder. Then, you can run your iron around all of the pins quickly to melt it all, and lift the chip off of the board. I have used this product or about 15 years. I believe it is the safest method for removing many ICs and other SMD devices.

[budm]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

I cut the leads on the IC when I need to remove the bad one. I would also repalce all 4 MOSFET's at the same time. They use Bridged output setup topology for driving the inverter transformer.

[cmj21973]

Re: This Guy was About to Put His Toshiba 37AV500U Into the Dumpster.....

SM soldering is like painting. It's all in the prework before painting/ soldering.
Just take your time and don't be in a rush.

http://www.bing.com/videos/search?q=...st=0&FORM=LKVR