Another Toshiba 42HP66 NO PICTURE, SOUND OKAY

[Truncatedhose]

Greetings!

I am new to the forum and I see a lot of these models with this symptom. I'm working on one that is stumping me and hoping to get some help. I suspect the Y-SUS, however none of the fuses are bad, which makes me a little doubtful. The IPM heatsink never gets warm, while conversely the Z-SUS heatsink DOES indeed get warm. I would suspect a bad IPM on the Y-SUS, but the lack of a blown fuse makes me wonder. Can anyone offer any help?

I also pulled the Y Drive/buffer out and measured it for shorts, but it seems to be fine. My next step is to pull the Y-SUS and check the IPM for shorts using this guide:

http://blog.coppelltvrepair.com/2011...s-ipm-for.html

I will see what I find.

When the IPM blows, do the fuses sometimes remain intact?

Okay, so I pulled the Y-SUS board and the Y-SUS IPM measures okay in the 6 tests Coppell TV lists. I can't seem to be able to find a problem on the Y-SUS. I then pulled the Z-SUS and it's IPM also checks okay.

If anyone has run into one of these sets with no bad fuses, but symptoms of a bad Y-SUS, please reply! Thanks!

[Shinju]

Re: Another Toshiba 42HP66 NO PICTURE, SOUND OKAY

Its going to be the Ysus/IPM out of the 2 I have had both suffered from a blown IPM and the fuses on the Ysus were fine.

Capkid, if he has time to post can tell you these LG Ysus suffer from this on these Toshiba panels.

I would start there.

[Truncatedhose]

Re: Another Toshiba 42HP66 NO PICTURE, SOUND OKAY

Its going to be the Ysus/IPM out of the 2 I have had both suffered from a blown IPM and the fuses on the Ysus were fine.

Capkid, if he has time to post can tell you these LG Ysus suffer from this on these Toshiba panels.

I would start there.

Thanks for the quick reply! Glad to hear that this has happened before and the fuses were fine but the IPM was still bad. The TV's owner DID report that classic loud pop or "fire cracker" noise when the set went out.

What do you think about the test that Coppell TV talks about? I was concerned when the IPM seems to test fine according to those tests between certain pins for shorts.

[Shinju]

Re: Another Toshiba 42HP66 NO PICTURE, SOUND OKAY

I don't know, I get panels from sources that I never interact with the original owners as they drop them off to get recycled.

Coppell seems to be a pretty place and a good knowledge base.

If you have another LG matching YSUS that you know works you can try putting it in and see. Do you get any screen prime? turn the lights off and power on the set and see if the panel primes at all (faint glow).

[Truncatedhose]

Re: Another Toshiba 42HP66 NO PICTURE, SOUND OKAY

I don't have any exact boards to put in and test, but I will put the boards back in and see if there is any prime at all. I looked for that originally, but didn't look REAL close with the lights off. It didn't seem to have any glow, but I will look again very carefully this time and see.

[Truncatedhose]

Re: Another Toshiba 42HP66 NO PICTURE, SOUND OKAY

Okay, I can't see any glow at all, so I would say no prime. Does this back up the bad Y-SUS diagnosis?

Are there other tests I can do to confirm that I don't have a bad main or control board or something else? Is there a way to leave certain boards unplugged to make sure it's not the Z-SUS or the Buffer? I forget which models you can and can't do that safely on.

[Alastair E]

Re: Another Toshiba 42HP66 NO PICTURE, SOUND OKAY

I have had both Y-SUS and Z-SUS IPM's failed, No shorts and no blown fuses on different sets.....
--So yes its possible that a faulty IPM cannot be tested by looking for a short or a blown fuse....

Only way to test an IPM is dynamically, ie--locating its inputs and the outputs, attach a load--say, a 12V bulb at 50W to a 12V battery, a separate 12-15V supply for the driver chips inside the IPM and a sig-generator running at around 20-60KHz square-wave at 5V P-P to drive the thing to conduction.....

One of the four IGBT stages (Assuming YPPD-J018C typical of a LG 720p set) of the IPM MUST be driven by an AC signal or it will appear as faulty, (Internally, AC Coupled) so might as well use the sig-gen to drive 'em all during the testing.

--For good measure, you can hitch a scope to the output and see how cleanly the thing is switching.

IPM's sometimes--say, 50/50 fail O/C Ive found, so no obvious measurable failure with 'cold-tests'.....

[Truncatedhose]

Re: Another Toshiba 42HP66 NO PICTURE, SOUND OKAY

I have had both Y-SUS and Z-SUS IPM's failed, No shorts and no blown fuses on different sets.....
--So yes its possible that a faulty IPM cannot be tested by looking for a short or a blown fuse....

Only way to test an IPM is dynamically, ie--locating its inputs and the outputs, attach a load--say, a 12V bulb at 50W to a 12V battery, a separate 12-15V supply for the driver chips inside the IPM and a sig-generator running at around 20-60KHz square-wave at 5V P-P to drive the thing to conduction.....

One of the four IGBT stages (Assuming YPPD-J018C typical of a LG 720p set) of the IPM MUST be driven by an AC signal or it will appear as faulty, (Internally, AC Coupled) so might as well use the sig-gen to drive 'em all during the testing.

--For good measure, you can hitch a scope to the output and see how cleanly the thing is switching.

IPM's sometimes--say, 50/50 fail O/C Ive found, so no obvious measurable failure with 'cold-tests'.....

Thank you kindly for all the good information, good sir! I don't know if I could safely or easily set up such a test jig or if it would be time/cost effective. I am thinking I will have to go with the "Y-SUS heatsink is cold and the Z-SUS heatsink is warm, hence the Y-SUS is not operating" hypothesis. I think I will order the Y-SUS as I can get a rebuilt board for about $50.00 surprisingly.

If anyone else wants to chime in before I do so, that would be tremendous!

On a side note: I am also dealing with the larger 50HP66 right now (I see one of these in my shop for repair about twice a month) and it had the "flashing, dark raster" symptom that usually is a Y-SUS, but after swapping with another Y-SUS, I get the exact same symptom as the 42HP66 we are talking about here and I think the board I swapped in has a different kind of failure than the failure that causes a "flashing, dark raster". I had kept it for a couple years in a box labeled "unknown boards". Of course the 50HP66 and 42HP66 Y-SUS boards are not interchangeable, otherwise I could swap things even more.

As far as 50HP66 Y-SUS boards, can anyone confirm if the 6871QYH039A and 6871QYH039B are indeed interchangeable?

[Alastair E]

Re: Another Toshiba 42HP66 NO PICTURE, SOUND OKAY

Well--The warm/cold IPM heatsink is a fair test as any I guess, at least with no other visible faults it does indicate that the (Cold) IPM isnt passing any current...

A check of the voltage across that row of red film-caps can sometimes indicate problems with the ER side of the IPM--Or in the case of the 50" The dedicated ERC IPM....

On the 50" sets Ive seen (Not many, about 3) That had issues, two had faulty ERC IPM's on the X-SUS boards.
--They ran stone cold, while the SUS IPM's were warm--The third set had a short SUS IPM and was gutted for parts for the other two!.....

As far as I know--there shouldn't be any problems switching a 'B' for an A suffix board in these sets...
--When you finally suss whats wrong and get the set running--Its well worthwhile changing all the 33uF and 68uF surface-mount caps around the DC/DC Converter stages, Use 100uF and 47uF caps as replacements. These caps are in the DC/DC converter run off the main 5V line deriving two floating 15V and a floating 5V supply that run the IPM's amongst other things.....

[mmartell]

Re: Another Toshiba 42HP66 NO PICTURE, SOUND OKAY

What's wrong with the caps/values already there ?

[Truncatedhose]

Re: Another Toshiba 42HP66 NO PICTURE, SOUND OKAY

Well--The warm/cold IPM heatsink is a fair test as any I guess, at least with no other visible faults it does indicate that the (Cold) IPM isnt passing any current...

A check of the voltage across that row of red film-caps can sometimes indicate problems with the ER side of the IPM--Or in the case of the 50" The dedicated ERC IPM....

On the 50" sets Ive seen (Not many, about 3) That had issues, two had faulty ERC IPM's on the X-SUS boards.
--They ran stone cold, while the SUS IPM's were warm--The third set had a short SUS IPM and was gutted for parts for the other two!.....

As far as I know--there shouldn't be any problems switching a 'B' for an A suffix board in these sets...
--When you finally suss whats wrong and get the set running--Its well worthwhile changing all the 33uF and 68uF surface-mount caps around the DC/DC Converter stages, Use 100uF and 47uF caps as replacements. These caps are in the DC/DC converter run off the main 5V line deriving two floating 15V and a floating 5V supply that run the IPM's amongst other things.....

Thank you, Alastair E. What voltage should I look for on that row of caps on the 42HP66 and on the ERC IPM on the 50HP66?

[nwmgnt2011]

Re: Another Toshiba 42HP66 NO PICTURE, SOUND OKAY

ysus board 6871qyh039b

no fuses blown, i found though one white pin GND/+5V/GND/VNSC/OC1/OC2/DATA/STB/GND/CLK/GND

the 2nd GND does not ground, but the VNSC pin grounds continuity with ground. is that my short?

if so what in pic do i need to change?

[nwmgnt2011]

Re: Another Toshiba 42HP66 NO PICTURE, SOUND OKAY

here is the pic of the ysus where i think i found a short