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Hi everybody,
I have recapped a Game Gear. The unit has now a black screen and the contrast wheel doesn't do anyting. The backlight is working correctly (I had to bypass the FU1 fuse). The games seem to boot up correctly, the sound from the unit is working fine.

I have already check with a multimeter the contrast wheel itself and it seems correct. I have try to reflow my new capacitors, without success. I have also reflow and test with a multimeter all the diodes and transistors. For now, I didn't see any broken traces.

Do you have any clue tlo help me with this issue ?

Thank you very much to your help !

There is probably a broken trace or via for the contrast circuit, it's not always visible you have to probe around for continuity, in particular the A, TPR1 and TPR2 signals.

Many thanks for your answer.
I have probed most of the traces of your schematic and, unfortunately, I have not found any broken trace or via.
Is there somes voltages that I can check, or some other tests that i can make to help me to locate the problem ?
If i am not able to resolve this, can I install a McWill lcd on this logic board or this issue will avoid it ?

I posted this at another thread but:

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.

There are some signals that can only really be checked with an oscilloscope to see the correct waveform.

Regarding the earlier signals make sure continuity between:

R41 and A on the ASIC
R43 and TPR2 on the ASIC
R44 and TPR1 on the ASIC

you can check which pins are A, TPR2, TPR1 for single and duel ASIC here:

https://retrosix.wiki/reading-game-cartridge#mk-2-asic-pinout

https://retrosix.wiki/reading-game-cartridge#cl-1-asic-pinout

Those three continuities are good.
However, I mesure incorrect voltages. I obtain 9.4v for R35 that seems quite good but only 3.4v for R46 and 7.9v for R47.

That would possibly suggest an issue with C54 & C55, or the two transistors they connect too.

I think that Q10 is the faulty I mesure only 0.95v on one junction with my multimeter in diode mode while I mesure about 1.8v on the same junction on a functional board.

The proplem does not come from the Q10 transistor.
I had swap the Q10 and Q11 transistors with ones from a for parts boards and it changed nothing. However, I have discovered that the "junction voltage" that I mesure doesn't come from the transistor wich doesn't have junction between these two pins but from somewhere else in te circuit. Indeed, I can make the same mesures on the pad with the transistor unsoldered. I have a junction voltage of 0.94v on Q10 and Q11 (see the linked for the pins that I mesure) on my board while it should be about 1.8v.

Capture d’écran 2021-12-20 à 19.22.26.png (162.2 KB)

I have re-checked all the diodes and transistor. I have found the same kind of issue on a Q6 junction (OL on my board vs 2.1v on a functional board). All the others mesures seems quite good to me.
Is there others components that I can check (I don't have an oscilloscope) ?
Thank you again for your help and time.

Capture d’écran 2021-12-20 à 21.06.52.png (177.31 KB)

This issue seems pretty hard to fix...
Will a McWill Lcd works despite of it or the contrast circuit need to be functional ?

I don't know the answer to that. My understanding is that most LCD mods will bypass the contrast circuit (but they still use the contrast wheel for brightness control and it may be necessary for at least a partially working circuit).

You are better off asking the vendor that question.

ok, thank you for your help.

Author	Message
n3rd Joined: 17 Dec 2021 Posts: 10	Game Gear Contrast wheel not working (recapped board) Posted: Fri Dec 17, 2021 6:09 pm
n3rd Joined: 17 Dec 2021 Posts: 10	Hi everybody, I have recapped a Game Gear. The unit has now a black screen and the contrast wheel doesn't do anyting. The backlight is working correctly (I had to bypass the FU1 fuse). The games seem to boot up correctly, the sound from the unit is working fine. I have already check with a multimeter the contrast wheel itself and it seems correct. I have try to reflow my new capacitors, without success. I have also reflow and test with a multimeter all the diodes and transistors. For now, I didn't see any broken traces. Do you have any clue tlo help me with this issue ? Thank you very much to your help !

thatawesomeguy Joined: 25 Jul 2007 Posts: 729 Location: Melbourne, Australia	Posted: Sat Dec 18, 2021 1:11 pm
	There is probably a broken trace or via for the contrast circuit, it's not always visible you have to probe around for continuity, in particular the A, TPR1 and TPR2 signals.

n3rd Joined: 17 Dec 2021 Posts: 10	Posted: Sat Dec 18, 2021 11:06 pm
n3rd Joined: 17 Dec 2021 Posts: 10	Many thanks for your answer. I have probed most of the traces of your schematic and, unfortunately, I have not found any broken trace or via. Is there somes voltages that I can check, or some other tests that i can make to help me to locate the problem ? If i am not able to resolve this, can I install a McWill lcd on this logic board or this issue will avoid it ?

thatawesomeguy Joined: 25 Jul 2007 Posts: 729 Location: Melbourne, Australia	Posted: Sun Dec 19, 2021 12:05 pm
	I posted this at another thread but: 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. There are some signals that can only really be checked with an oscilloscope to see the correct waveform. Regarding the earlier signals make sure continuity between: R41 and A on the ASIC R43 and TPR2 on the ASIC R44 and TPR1 on the ASIC you can check which pins are A, TPR2, TPR1 for single and duel ASIC here: https://retrosix.wiki/reading-game-cartridge#mk-2-asic-pinout https://retrosix.wiki/reading-game-cartridge#cl-1-asic-pinout

n3rd Joined: 17 Dec 2021 Posts: 10	Posted: Sun Dec 19, 2021 1:03 pm
n3rd Joined: 17 Dec 2021 Posts: 10	Those three continuities are good. However, I mesure incorrect voltages. I obtain 9.4v for R35 that seems quite good but only 3.4v for R46 and 7.9v for R47.

thatawesomeguy Joined: 25 Jul 2007 Posts: 729 Location: Melbourne, Australia	Posted: Sun Dec 19, 2021 1:15 pm
	That would possibly suggest an issue with C54 & C55, or the two transistors they connect too.

n3rd Joined: 17 Dec 2021 Posts: 10	Posted: Sun Dec 19, 2021 1:46 pm
n3rd Joined: 17 Dec 2021 Posts: 10	I think that Q10 is the faulty I mesure only 0.95v on one junction with my multimeter in diode mode while I mesure about 1.8v on the same junction on a functional board.

n3rd Joined: 17 Dec 2021 Posts: 10	Posted: Mon Dec 20, 2021 7:11 pm
n3rd Joined: 17 Dec 2021 Posts: 10	The proplem does not come from the Q10 transistor. I had swap the Q10 and Q11 transistors with ones from a for parts boards and it changed nothing. However, I have discovered that the "junction voltage" that I mesure doesn't come from the transistor wich doesn't have junction between these two pins but from somewhere else in te circuit. Indeed, I can make the same mesures on the pad with the transistor unsoldered. I have a junction voltage of 0.94v on Q10 and Q11 (see the linked for the pins that I mesure) on my board while it should be about 1.8v. Capture d’écran 2021-12-20 à 19.22.26.png (162.2 KB)

n3rd Joined: 17 Dec 2021 Posts: 10	Posted: Mon Dec 20, 2021 8:11 pm
n3rd Joined: 17 Dec 2021 Posts: 10	I have re-checked all the diodes and transistor. I have found the same kind of issue on a Q6 junction (OL on my board vs 2.1v on a functional board). All the others mesures seems quite good to me. Is there others components that I can check (I don't have an oscilloscope) ? Thank you again for your help and time. Capture d’écran 2021-12-20 à 21.06.52.png (177.31 KB)

n3rd Joined: 17 Dec 2021 Posts: 10	Posted: Sun Dec 26, 2021 11:59 pm
n3rd Joined: 17 Dec 2021 Posts: 10	This issue seems pretty hard to fix... Will a McWill Lcd works despite of it or the contrast circuit need to be functional ?

thatawesomeguy Joined: 25 Jul 2007 Posts: 729 Location: Melbourne, Australia	Posted: Mon Dec 27, 2021 6:16 am
	I don't know the answer to that. My understanding is that most LCD mods will bypass the contrast circuit (but they still use the contrast wheel for brightness control and it may be necessary for at least a partially working circuit). You are better off asking the vendor that question.

n3rd Joined: 17 Dec 2021 Posts: 10	Posted: Mon Dec 27, 2021 11:55 am
n3rd Joined: 17 Dec 2021 Posts: 10	ok, thank you for your help.

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