BenQ 46W1 bad Y-sustain. what should test point pads read?

[sugar_ray]

have a BenQ46w1 second gen. plasma. been troubleshooting in my spare time. It has screen glow but no picture.

what i have done so far
-----------------------

-tested power supply board (good)
-borrowed an osiliscope and tested the buffer boards (variable voltage good)
-discovered a blinking (busy signal) red LED light on the logic board. according to a BenQ tech, this indicates the unit is in shutdown mode.
-confirmed that there is NO service menu or codes for this model
-99.9% sure the panel is still good. NO humming,cracks etc....


i picked up a good used logic board for $25. a swap did not fix the problem.

what looks suspect to me, and maybe someone with more experience can chime in, is the Y sustain board itself. I have access to a few of them that have a $59 price tag. Just want to further test before dropping some $$$$.
On the Y-sustain board itself (not buffers) it has about 6 solder pads labeled (TP1, TP2, etc...) I gather TP stands for "TEST POINT"

first question.....are these pads variable voltage or should a standard multimeter be showing something? using the meter I get ZERO reading off of TP1 and TP2. the other pads are throwing out voltage just nothing from 1 and 2?? when I test the Z sustain board it gets voltage from ALL TP pads.

gut feeling tells me to replace the Y sustain but would like to test further.

penny for your thoughts.........

[tom66]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

Here is what a Y-sustain waveform should look like, for reference:
https://www.youtube.com/watch?v=nGr5ydz9gTk

You should test the main outputs going to the buffer boards.

If the screen is glowing, the Y-sustain is -almost- certainly good.

[cliff_hootarski]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

In that video at the 8:36 time, did he say metric fuck ton of RF interference.
Is that an industry standard?

[tom66]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

In that video at the 8:36 time, did he say metric fuck ton of RF interference.
Is that an industry standard?

Yes, I did say that.
It's approximately equal to ten shit-tons of RF interference, or about 90dBµV (conducted.)

[cliff_hootarski]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

I'll keep this in mind. It could be usefull someday.

[sugar_ray]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

thanks for the tutorial. will re-borrow that scope and conduct more tests. it is one of those Chungwha plasma panels. rare, yes but the principles seem to be the same. while doing parts research. A lot of gateway stuff is compatible with this set.

QUOTE TOM: If the screen is glowing, the Y-sustain is -almost- certainly good.

all this is "best guess" work anyways. given a replaced logic board, good power supply and screen glow. what would your best guess be? Interestingly enouh.....If I unplug the power harness that leads to the sustain and power on the unit I "STILL" have screen glow even though no power is being applied to the Y board. does this tell me anything??

[tom66]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

I've done a little research on CPT plasma panels...

They made them from 2004~2006 then left the business to focus on LCD tech (they're probably kicking themselves now because plasma has moved into a niche of high prices and high margins whereas LCD is a race to the bottom.)

Some of the technology is similar to Hitachi/Fujitsu plasma panels (aside from TERES and ALiS), so perhaps some technology sharing/theft went on. Though a lot of innovative research and development was obviously done because they've got a very unique design. It appears to use no electrolytic bulk capacitors on the sustains -- very good for reliability & less of a shock hazard to work on. I've never seen so many FPGAs on one control/logic board -- low cost ones, but you can easily see the signal paths, so that's nice. And it doesn't look under-engineered at all...

SM for 46" Vizio based on CPT plasma panel (more than likely the same as yours):
http://www.tgohome.com/ServiceManual...&Search=Submit

I'm really not sure which side the buffers are on. The service manual is completely unclear -- it seems to suggest they are on the X-Sustainer (by the orientation of the TV), but this seems a little unusual. Can you locate the buffers? A picture is shown on page 41.

My bets are on the video board. The logic board is driving the plasma panel to display exactly what it is being told to: Nothing. An older plasma panel like this will glow due to the priming circuit, and that's generated on the scan board (the sustainer which connects to the buffers.)

[sugar_ray]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

thanks for another informative post tom. yes i can locate the buffers. they are attatched to the y sustain via ribbon cable all be it hidden under the internal speakers. not a big deal to get at them. buffers have good waveform or so it seems.

you mentioned your bets are on the "video board" would you be referring to the "digital main" video board that houses the DVI and VGA inputs? I am only assuming you don't mean the logic board becuse I swapped that one with a known good working one.

interestingly enough......the blinking red LED on the logic board, which according to BenQ techs, indicates a problem. , will not blink if i disconnect the power harness from the digital main. removing the harness removes the blinking RED LED which then switches to solid GREEN led. However, removing the power from the digital main also loses my screen glow.


when this model is working properly the LED on the logic will be solid green and not blinking red like it is now.

So I hope this is the video board you are referring to?? this is the one for my unit. Should aslo mention that audio is working fine. just no display

[tom66]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

Perhaps it is in "busy error" because it is receiving no video?

I do not think this chassis has a test mode, which is a shame. You can try scoping the outputs going to the logic board -- if you don't see anything there, I'd suspect that board in your post, which is the video board. I'm guessing this TV also has a separate board for analog video inputs?

[sugar_ray]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

when it was working and had NO video signal you would still have a display indicating no input etc..... and you could still activate the menu screen. this chassis has no test mode which sucks the big one!! YES there is a seperate board for the analog input. will scope lter this evening and if i find nuttin.......I will be on the "should i spend $50" and gamble on the video board fence??

thanks for all your input

[tom66]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

What I meant is the plasma control board (the logic board) may be signalling a busy event because the main board isn't sending it any video, not even an OSD saying "no video".

[sugar_ray]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

No worries Tom......I caught your meaning. thanks for the many less experienced users you have helped on these boards.

[sugar_ray]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

well Tom......a sad day indeed. My digital main board arrived $45. All excited I put it in with high hopes. just to see the damn red busy blinking light!! Still have glow and audio just no picture. If i disconnect the power harness from this board the busy light turns to a solid green (which is what we want for this model) but I then lose my glow.

RECAP: I replaced the logic card $25 and the digital main $45. $70 in and i think I will just have to accept defeat at this point?? I would really hate to scrap this set because with glow you would think it could be something worth saving?? Both sustain boards give off nice heat through the sinks after a few minutes of use. Other then the buffers which seem to measure ok on the scope I am at a complete loss. I have located a few locations that have virtually every board I would ever need for this set BUT at this stage I appear to be guessing WRONG. Not the end of the world by any means but a little disappointed I couldn't save her.

Guess the old saying goes......."most of the time it is cheaper to purchase a new one then it is to fix them" I know....I know....where is the fun in that??

But with 2 buffers connected to the the Y sustain board, 2 buffers connected to the Z sustain, and another connected to the logic board. It would be just too expensive to find this gremlin??

try talking me out of giving up??

[tom66]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

Have you scoped the Y-sustain output yet?
Giving up would be easy and simple but would leave you unsatisfied.

[sugar_ray]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

Have you scoped the Y-sustain output yet?
Giving up would be easy and simple but would leave you unsatisfied.

unsatisfied is the key word my friend!! i hate to lose, but I also hate to just throw money at it unnecessarily. Ok.....will re-borrow that scope and give it one last crack. Your suggesting a bad Y-sustain "output" will cause glow but no picture. In essence, a bad Y-out would require a replacement Y. I only half know what im doing with the scope so I shall snap some pics to get me on the right track. i thought (and could be VERY wrong) that if you have glow then your Y was almost always good??

[tom66]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

I just want to verify if the Y-sustan is producing the right signals. If it is, we can rule it out, along with the Z-sustain/X-sustain.

[sugar_ray]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

ok......Tom after a few days off I am bound and determined to crack this sucker!! I was able to talk with a tech guy from the place I have purchased my 2 parts from. Very knowledgeable and helpful. Just want to confirm a couple of things with you before proceeding. We were able to determine this is nothing more then "GATEWAY" boards or "AKAI" as BenQ never made their own displays back then. Just re-branded as Ben-Q

In a previous post you mentioned "This design of plasma panel has reversed naming. The X-scan (Y-sustain) looks to control the vertical scanning, and the Y-bulk (Z-sustain) looks to provide the alternate sustain electrode waveform."

At first this threw me off as I was looking at the board labeled "Y-Bulk" (left hand side of the first picture) and assuming that Y-Bulk meant Y sustain??
The board labeled X-scan has a ribbon cable coming off of it attached to the logic board and is my Y-Sustain correct??? Right hand side of the first picture.

My second picture shows a better view of the X-Scan (Y-sustain) board. It appears to have 2 buffers growing out of it. what I am not sure of, is which one of the 2 drives the video?? As a test.....I unplugged the buffers one at a time then turned the tv on. I can still get screen glow with one of the specific buffers unplugged. However whwn the other is unplugged I lose my screen glow. Would it be too much to assume the one with no glow while unplugged is the Y-buffer that drives the video??

The tech I spoke with (works on all makes and models) is fairly confident that since I replaced the logic board and digital main with no luck that the problem is either a bad Y-sustain or bad Y-Buffer. Both fairly inexpensive.

So with my scope can you (by looking at my pictures) indicate where i should be getting good waveform if any??

Lastly....almost all places that sell these used parts must also be assuming that Y-bulk mean Y-sustain??? cause that's what they are advertising them as!! On this rare model everything seems to be in reverse. good for me I guess, cause a Z-sust. usually sells for cheaper then a Y.

[tom66]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

Here is where I think you should probe.

Now, perhaps it is possible the design has moved the priming circuit onto the Y-bulk. This would leave you with a glowing screen, no picture, if the X-scan failed. Just a thought...

Those boards do look like buffers but since they're upside down I can't be sure.

I'd order by part code instead of "Y-sustain" etc.

[sugar_ray]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

the more I learn about this set the more I am discovering it is a "dinosaur" compared to recent displays?? Like why are there 2 buffers when most other sets only need 1 to survive??
One of them labeled "X-EXT L PCB" and the other labeled "X-EXT U PCB"

Here is a better picture of those 2 buffers when removed from the sustain board. I am trying to get documentation confirming that Y-Bulk = Z-sustain
and X-scan = Y-sustain on this model. Tom you sounded pretty sure in a previous post that this was the case?


My huntch says your right because disconnecting the power harness from the X-scan means losing my glow. If I unplug the power harness from the Y-Bulk I still get a glow.From what I have gathered you absolutely need your Y-sus. powered up to achieve glow. A non powered Z-sus. will still give you something as I seen through experimentation

anyways.....won't get around to probing until this weekend. That stupid thing called work, ya know!! Will try your advice and post my results now that I have an idea of where to probe.

P.S> Is there any specific reason you choose that location to probe? Just so I am learnin' somethin'

as always Tom.....your input is appreciated

[tom66]

Re: BenQ 46W1 bad Y-sustain. what should test point pads read?

One vs two buffers is simply a cost decision.
One buffer fails = Half picture still visible, easier to diagnose for the tech.
But costs more to implement than a single board.

It's only a WVGA display, so not HDTV. I don't work on these any more because they aren't worth much. I see them regularly listed for around £60~£70 here.

Chose that location for convenience. Easy to hook scope probe on to. You can see the large output plane there.