CurtPalme.com Home Theater Forum

[gjaky]

I ran a strange -but not so serious- problem with my NEC 6PG xtra. I use it regularly in 720P@72Hz, but now I started to play with 1080i-60Hz. When I set up the new preset I copyed the convergence data from my 720P preset. All was great until I set something with the brightness, and the AKB turned on, and it messed up the white balance on 1080i, and since then I can't get the same white balance with the same settings in 1080i and 720P. Beside this the pj works fine, and my 720P preset is left untouched. Can someone explain what is happening?
Addition: the blue tube is driven very hard at 1080i, setting the blue black level to 0% still get too much.

[gjaky]

Okaay it seems this AKB thing affects my 720p setting as well... so when I turn on the pj everything is fine colorwise, but if I turn on AKB, the white balance jumps toward to a much colder shade. The last time I left the AKB on was about 50hrs ago, also AKB should keep white balance not messing up. After turning off the AKB the picture remains cold, but reselecting the input it jumps back to the original whitebalance setting.
Also if the AKB is engaged and I'm in the wite balance menu the white balance varies widely by it's own, if I exit from the white balance menu it gets stable again.
So far I've reseated the boards in the back cage, pushed all the pots (in case of contact problems) but it's the same.

[Tinman]

Well, I have just replaced about 25 rotten capacitors in my PG10plus. (Runco 990) White balance is working nice and stable now. The Video output boards have a few caps that are prone to leaking at this age. The Extra uses the same board, basically, with the final drivers remote mounted on the neck boards instead of a big heatsink on the video board. ALL PG series projectors are seeing leaking capacitors by now. The amazing thing is how long they keep working fine until something actually manifests itself.

Point is, these sets are at the age where this should be looked into.

Marc

[gjaky]

Oh well, I'll look at them when I'll have more time, until that I'll stay away from AKB
Thanks for the suggestion.

[gjaky]

I took a closer look at the gain ctl and the video out boards, even tested all caps in the blue section but no visual leak, measured and perfect capacitance and ESR with all caps, however this is a heat related problem: right after powering up the AKB control is working fine and as the pj warms up it shifts the blue black level more and more. Is there any point to recap the gain ctl board as well?

[CasetheCorvetteman]

Yes.

[CasetheCorvetteman]

But it seems more like you might be getting a bad solder joint Gjaky, like as if its getting a high resistance when the machine warms up.

[gjaky]

[CasetheCorvetteman]

This is above me now mate, you may remember i had a simular issue with my 9PG a while ago where the red was very dim at start up, and would then come good after the rig warmed up abit. I swaped every board except the little HV board in the back corner, and had no luck at all.

How many caps on the neck boards in the XTRA?

I know you tested all those caps and found them to be fine, but that is not at operating temp, id think it would be unlikely they would break down abit as the temp gets up, but i dont think its out of the question either.

I never did really get a dead certain fix on that issue with my 9PG, but pressing KELVIN would correct it at cold, perfect colour, then when warmed up, very bright red. Pressing KELVIN when warmed up would make colour fine again, and so i left it at that. Leaving the AKB turned on would mean it would stay fine all the time, but those lines are at the top. Replaced all the capacitors on the VIDEO OUT and that did reduce it abit. The variation between hot and cold was alot less.

Im not sure how simular my issue is to yours, seems abit different though.

[gjaky]

I remember that thread.

There are only four electrolytic caps on the neck board.

In my case the white balance is perfect unless I turn on AKB, so the problem is with the AKB circuit for sure. Unfortunately I am not fully aware with the operation theory of the AKB circuitry. I think the top line represents a constant drive signal for all three tube, and the machine measures the beam current (or something similar) of the constant drive portion of the screen and it calculates the emission loss of the tubes somehow, and correcting the drive considering the white balance settings given in the menu. It seems the wave board (or system board) have very wide control range over G2 (aka. black level), because if I turn G2 to 0%, AKB can drive blue G2 to light up the raster, while maintaining the blue white level (or at least almost). So my guess there is really a contact problem somewhere in the blue sensing circuitry which make it thinks the blue current is less, than it is in reality so it cranks up G2 to equal the error, this is most likely the case because with activated AKB the black level always varying a bit. The problem now is I don't know where is the actual sensing (and how it is) happening..

[CasetheCorvetteman]

Yeah see on the Plain and PLUS there are none on the neck board. Probably all i did do was fix some bad joints forming and replaced some caps on their way out, although majority tested out of spec.

What you say sounds plausable, i dont know how it all works or what it relys on to work correctly, so i cant really comment one way or the other.

I just wonder if there is a bad connection with any of the little plugs, or if they are dirty and need cleaning or whatever, see again in my case, i had the boards in and out a few times, and it got less, so maybe the removal and replacement of those connections cleaned them up a touch.

All speculation really isnt it!!

[Tinman]

I remember Doug telling me that the blue neck board was a common problem with the Xtra. One reason I stayed away from it.

Never did figure out what made them go bad.

Marc

[CasetheCorvetteman]

Are those neck boards the same on all 3 tubes with an XTRA? Ive never looked close enough. ( never needed to!! )

[gjaky]

Yes, all three neck boards are the same in construction, except for the installed cable length which makes them almost unswapable (for example: you can put B neck board on green, but you can't put G neck bd on blue tube)
To be honest I had one blue neck board failure with this 3500hrs ran machine, I only used this for ~400hrs and the failure came after <50hrs after buying, it sat in a very unfriendly storage room for a long time. In my case the video out IC went bad, and one protector diode went short, I don't know why. One big fan is only cooling the blue neck board, while the other two neck boards are not actively cooled (I remember from my 'marquee' era the blue neck boards produced much more heat than the other two there also -I don't know why)

Good news:
Yesterday I resoldered a bounch of things (again) on Neck board and on the video out board and since then it works fine, with turned on AKB, and finds the right color balance with the 'infected' presets too.

[CasetheCorvetteman]

Thats good mate, hopefully youve tracked it down eh!!