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View topic - GG in SMS mode. Is it flickering?

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  • Joined: 25 Feb 2013
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  • Location: Osaka
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GG in SMS mode. Is it flickering?
Post Posted: Wed Nov 03, 2021 8:46 am
I noticed that when put in SMS mode the GG the display appears to flicker/ sort of lightly flash white. Is it a problem with my setup or is it a common thing?
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  • Joined: 12 Apr 2005
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  • Location: London, United Kingdom
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Post Posted: Wed Nov 03, 2021 4:55 pm
Have you replaced the capacitors in your Game Gear? Flickering in SMS mode is quite common in Game Gears with failing capacitors in my experience.
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  • Joined: 25 Feb 2013
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Post Posted: Fri Nov 05, 2021 3:57 am
Yes, it is fully recapped with good (nichicon) caps
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Post Posted: Fri Nov 05, 2021 6:30 am
You may be onto something here. I tried on a different game gear and there's no flickering. It's not the caps, but it's something to do with the gg hardware nonetheless.
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Post Posted: Fri Nov 05, 2021 2:46 pm
I've had a couple of Game Gears that constantly flickered like crazy in SMS mode (but not in Game Gear mode) pre-capacitor replacement, and replacing the capacitors cured them. I'm not sure what the issue is and why yours is still flickering if you've replaced the capacitors, sorry!
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  • Joined: 25 Jul 2007
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  • Location: Melbourne, Australia
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Post Posted: Sat Nov 06, 2021 6:37 am
The LCD will flicker if there is a problem with the contrast/vertical sync circuit.

Starting with A, TPR1 & TPR2 should all be present, this is difficult to check without an oscilloscope because they are pulsed waveforms, but given the display works in GG mode I wouldn't expect them to be a problem.

Next is the 34v rail should be present and stable as that feeds into this part of the circuit.

You will see from the attached circuit diagram (from single ASIC, may be labeled differently on twin ASIC) there are quite a few capacitors, transistors, diodes, and resistors that feed this part of the circuit.

When SMS mode is enabled, the voltage to the contrast/vertical sync circuit is dropped slightly, if voltages to this circuit are bad then that is probably causing your flickering.

R35 should read 9-18v in GG mode, and 7-15v in SMS mode.

R46 should read 5-12v in GG mode, and 4-10v in SMS mode.

R47 should read 8-15v in GG mode, and 7-12v in SMS mode.
contrastcircuit.JPG (169.5 KB)
contrastcircuit.JPG

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Post Posted: Sun Nov 07, 2021 12:55 pm
Thank you for pointing out this section of the circuit!
It was the "charge pump section". Specifically, the trace between Q9's collector and C54 was damaged.
I would have thought the problem to be something closer to Q5, since that is the part affected mostly by the gg pin. The charge pump problem was there also for the GG mode. It seems, however, that the SMS mode shows the problem more markedly.
And it well matches the empirical observation by benryves. Probably usually the same charge pump is affected by the capacitors themselves, and not from the trace to them.
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Post Posted: Tue Nov 09, 2021 6:34 am
That is fantastic news and a win for LCD preservation.

I have a theory that many suspected faulty LCDs are in fact not faulty at all, and that people assume that no display after replacing caps means a faulty screen, but there's so many other contributors, the most common being damaged traces and vias.
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