Sega Game Gear diagnostics help needed

[technomacer]

Hello folks,

 

I am working on a Sega Game Gear (VA1 main board that, like most of them at this point, had leaky caps that I replaced with one of the many cap kits available on the net. The problem I am having is that, despite replacing the caps, the screen just shows up black. Some folks have had luck with reflowing the caps they replaced but of course I couldn't get off that easy. I was wondering if anyone had and experience with diagnosing issues with these units?

 

Here is what I have done so far:

• Replaced all caps on the sound, power, and main boards
• Checked continuity between the new caps and the next component in the circuit
• Measured the output of the power board (both 5v pins seem good as well as the 34v pin for the backlight)
• Checked that the backlight works (that one is obvious since it either comes on or it doesn't)
• Measured some of the points on IC1 as well as other points on the 5v rail and noticed that it is getting about 4.88v. Not sure if the voltage drop is expected or if that means there is an issue?

 

I found a schematic for this unit online but with my limited electrical engineering skills, I have no idea how to tell what things need to be present for these units to start. I would love to learn how to troubleshoot these issues (and how to better read that schematic) so any help anyone can offer would be greatly appreciated!

 

Here is a link to the schematic: Game Gear VA1 Service Manual

[+Stephen Moss]

I don't have any experience of the Game Gear but all computer systems need three key things to operate which should be the first things to check for...

Power - if power is not getting to part of the circuit or to all power pins on a device (particularly the processor, VCC & GND) then nothing will work. Check every power pin on a IC and connector but only the first component to which any point marked 5V or 35V is connected on the various sub-circuits otherwise you will be there for hours if you check it gets to every component. I would start at 5-3 DC-DC converter and the voltages on CN1.

Clock (Xtal) - difficult to check without an oscilloscope but a reading other than 5V or 0V on a DVM (multi-meter) is a likely indicator that the clock is running. Check it gets everywhere it needs to.

Reset - Resets are normally active low (0V, indicated by a line above it), it should be that at power one but quickly rise to 5V after a short delay to allow the power supply to stabilise and then remain there unless a manual reset is performed with the power on. Check it is correct everywhere it goes to.

 

So unless you get any better advice form someone experienced in Game Gear repair who may know specifically where to look I suggest you start by checking the items above as best as you can.

[technomacer]

Thanks Stephen! I ordered the AC wall adapter for it so I don't have to keep draining the batteries while I spend some time probing the board. Hopefully that will be in soon so I can start probing at it for a while.

[gamegrid2084]

A black screen usually means that the Game Gear cannot read or does not recognize any cartridge in the system. You should see the same result if you turn on the GG without any game in it. Troubleshooting this is made more difficult (or easy) depending on whether you have a unit with TMSS. TMSS (TradeMark Security System) presents itself to you in the form of a blue screen whenever you put a game in and start the system. The screen background is blue and there is white text that says "Produced by or under license from Sega Enterprises LTD" (or something like that). How does that help? Well, when the system is having trouble reading games, sometimes it can read some games easily and others not so much ... but, it usually will recognize that a game is in the system and you will see the blue TMSS screen (even if the game doesn't work after that). However, that is also not 100%, but it would help if you knew what you were expecting to see. If you don't have TMSS, then you won't see the blue screen and the game would just start up (or not, if the system can't recognize it). That makes things a bit harder. Some things to try:

 

1) Make sure you have more than just 1 game to test. Even if it works fine in another GG, the game may not be recognized easily by your newly recapped system. For me, Sonic the Hedgehog 2 seems to be easily readable even in Game Gears that you otherwise would have to insert -> take out -> insert-> take out -> insert ->... a cart until it sees the cart and plays the game.

2) Make sure that it's not some weird screen problem. If it recognizes the game, then you should hear game audio. Give the game you inserted enough time to play sound.

3) Check the voltage across the +/- of C1 (the 33uF 6.3+v cap). It should also be around 5v (and 4.88v is fine). That cap gives the cart the +5v it needs to run. The 5v line should hit 2 pins in the cart slot.

4) Make sure the brightness wheel does something. Moving it from minimum brightness to max brightness should still change how "black" the black screen is.

5) If want to get really serious, then you'd want to rule out cold solder joints in the cart slot. I have encountered this in only one out of 100 GG systems, so it's unlikely.

6) If all else fails and a visual inspection doesn't show any damaged traces, components, etc.. Then you'd have to work from your 1ASIC or 2ASIC chip(s) and start tracing from there...

7) One last thing to try is to completely disconnect your sound board and see if the rest of the system works. Don't ask why, it's just come up as a solution more times than I have expected.

 

If you have any questions, I'm happy to try to help.