CurtPalme.com Home Theater Forum

AFryia · Posted: Sat Mar 21, 2015 8:06 pm Post subject: Gain & Bias Issue

I just finished tweaking grey scale on my VPH-G70. I got her to <4de but I do have some concerns; what do you make of the following?

The GAIN are set G=253 R=145, B=170. Manual says to run green max or 255, but I get better grey scale knocking it down a bit.

Where my concern is with BIAS; G=0, R=60, B=MAX. Up until now GAIN and BIAS have always been the same order of magnitude.

I run;

Contrast - 70
Brightness - 39

.. so I'm surprised the G&B bias are at extremes. What could be the cause.?

gjaky · Joined: 05 Jun 2010 Posts: 2790 Location: Budapest, Hungary

Those are only numbers the AKB (ABG or whatever it is called in the sony) circuit has also effect on these numbers so unless you not probe the actual cathode and G1 voltages we can't say anything sure. But assuming all numbers directly corresponding to the actual voltages the blue cathode is wearing out therefore needs more drive, the green tube may show some sign of contamination therfore harder to shut it down, but also could be aging capacitors, bad (loose) connectors and so on...

CasetheCorvetteman · Joined: 09 Nov 2008 Posts: 6319 Location: Australia

Do you have the blue defocused enough?

AFryia · Posted: Sun Mar 22, 2015 1:27 pm Post subject:

CIR Engineering · Posted: Sun Mar 22, 2015 4:29 pm Post subject:

What firmware version do you have on your G70? I think the final firmware uses AKB (auto cathode balance), but that the easily firmwares allowed direct access to the G2 settings. If you have the firmware that allows for G2 setting than you should do that before you try grayscale. If you have the version that supports AKB, than you should run the AKB for 20 minutes, turn it off, and then do your grayscale.

You can upgrade your firmware, but I seem to recall liking the older firmware better. I also seem to recall that you can't go backwards easily with the G70 firmware's.

It's been years since I have worked on a G70 so it's getting fuzzy for me.

Also, on the G70 you should set your brightness to 50 and your contrast to 80 and leave it there. They set your GREEN gain to between 190-225 and then keep it there. Adjust your RED and BLUE gains to balance the high grayscale. Adjust your bias for RED, BLUE, GREEN such that you reach the correct black level when all three also make D65 gray. Start be setting green so that you can just barely see a 1-2 IRE bar and then adjust RED and BLUE around it.

all will interact so it's important to keep GREEN gain constant while you work. The older the tubes the higher you will need to set GREEN gain when you start to get a good white point.

Leaving brightness and contrast at their defaults of 50/80 will yield the best gamma curve for the G70.

Good luck!
craigr

AFryia · Posted: Sun Mar 22, 2015 5:25 pm Post subject:

Craig,

Thanks for the tips I try them next weekend.

As for the firmware I can switch back, I have a complete set of B boards (I think its B for PROMs and CPU) in my service/spare chassis. I switched to the newer version for the improved memory management. Both firmware have the AKB control.

You learn something new every day; I didn't know to turn off the AKB for grey scale.

Thx! Thumbs Up

CIR Engineering · Posted: Sun Mar 22, 2015 8:31 pm Post subject:

CIR Engineering · Posted: Sun Mar 22, 2015 8:38 pm Post subject:

Here are a few links to AVS where Bruce was helping folks with G70 issues like yours.

http://www.avsforum.com/forum/16-crt-projectors/568806-set-g2-sony-g70.html

http://www.avsforum.com/forum/16-crt-projectors/723254-g70-g2-gain-bias-settings.html

http://www.avsforum.com/forum/16-crt-projectors/614395-g70-g2-setting-anyone.html

AFryia · Posted: Mon Mar 23, 2015 10:53 pm Post subject:

I'll quickly try resetting brightness and contrast to default and give that a go. If that doesn't do it I'll switch back to the old firmware and see if it is any better.

Dumb question Shocked

The old firmware lets you adjust the G2, but where are the settings stored? Is it seperate from the firmware on a different PROM? How did the factory adjust G2 with new firmware?

CIR Engineering · Posted: Mon Mar 23, 2015 11:15 pm Post subject:

CIR Engineering · Posted: Mon Mar 23, 2015 11:23 pm Post subject:

Also, the Dallas chip is socketed and the firmware IC is soldered.

craigr

mac · Joined: 07 Nov 2012 Posts: 143

Battery backup S-ram chip(also called dallas) is ic308 on YB board. It is a M48Z128Y.
ic103 on the YA board is the program ROM chip.
G2 control chip is ic400 on the YB board.

CIR Engineering · Posted: Tue Mar 24, 2015 1:28 pm Post subject:

Thanks Mac!

I was hoping you would jump in Smile

craigr

AFryia · Posted: Sun Mar 29, 2015 3:46 pm Post subject:

Craig Thanks!

I stayed with the new firmware and started with your recommendations. Grey scale is good again, de 1.07 avg, max 2.15. Gamma is a little high 2.4 avg, 2.9 at the bottom working down to 2.2 at 100IRE.

I do not use a video processor. What can I do to leveling off the gamma especially the lower IRE?

Contrast 80
Brightness 50
Bias R=208 G=77 B=192
Gain R=104 G=225 B=111
Temp: Preset
ABG: Off
Memory #10
Brightness Uniformity: Standard
Color Uniformity: Standard
Screen: 2
Clamp: Auto

CIR Engineering · Posted: Sun Mar 29, 2015 4:41 pm Post subject:

AFryia · Posted: Mon Mar 30, 2015 10:59 pm Post subject:

CIR Engineering · Posted: Tue Mar 31, 2015 1:51 am Post subject:

John's board is the perfect one to have for the G70. It will do 1080p 60Hz with almost no attenuation in BW. You only can run RGB, but that's a worthy compromise.

John's card won't do 1080p 72Hz, but neither will your G70 (well), so no matter.

The card is designed for RGB 0-255. I usually go ahead and run them at 16-235 and adjust bias and gain to compensate. It sounds like that's what you've done so it should be well setup.

craigr