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Sega CD

Atari Lynx I: Sudden Death! Voltage Too High?

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Hi folks,

 

I have a Lynx I that I performed the McWill mod on, replaced all electrolytic caps, and replaced all the usual transistors (Q11, Q13, Q4). I've put maybe 3-4 hours on it since the mod. No issues.

Yesterday, I received my Lynx GameDrive and immediately began to party down with it. All was good for the first hour or so of use. I was playing the "Lynxed by Desire" demo and reached the point with the rotating 3D dodecagon or whatever when, suddenly, the dodecagon started "painting the screen" with every frame or so frozen to the background while it continued to rotate. Then the music stopped...and the screen shifted so it wrapped around the screen about 50%, accompanied with some random blinking pixels here and there. "What a weird demo," I thought... After staring at this frozen screen for a few seconds, I realized this was not normal, and turned the Lynx off. I powered it back on and was met with a rapidly blinking "Insert Game" with more odd blinking pixels.. But the flash cart was still inserted. I removed the flash card and was surprised to see that it still started without a game inserted!!! I thought maybe a pin in the cartridge slot was bent. Nope... "Oh no" I thought. Turning on and off the unit, the system alternated between the glitched "Insert Game" screen, static multicolored "noise", and something in between.

 

At this point, I opened up the unit thinking maybe something shorted. All my wiring looked fine, nothing stood out...but after powering the unit on and poking around a bit, I noticed that I was reading 7.7V across the vias that once caressed pins 1 & 2 of the power module. Uh oh. That should be around 5V, right? I immediately shut off the system in fear of the worst. I'm wondering if the only reason why I was getting 7.7V instead of 9V was because I was running off of batteries and the voltage was sagging.

So my poor once-super-powered Lynx I is sitting in front of me, guts hanging out and hanging onto life by a thread. Does anyone have any ideas on what might be the culprit? My suspicions are on an untimely demise of U6 which has some decent corrosion due to battery acid, but the (accessible) traces test fine with a DMM. I'm just a little tripped out because usually Lynxes wont power up at all...while this guy will power up with nothing inserted! I'm also afraid to power up the unit and possibly hurt it worse than it may already be.

 

Has anyone heard of or tackled this issue before? If so, any pointers on what devices I should check?

 

Thanks!

Edited by Sega CD

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Posted (edited)

I finally fixed my Lynx. In case anyone bumps into this thread in the future and has similar issues, here is a run down of what happened...

 

I ended up replacing U6 with a NOS Motorola MC14069B from eBay almost immediately after posting this thread. I'm not completely sure what happened, I think something changed (I think now it didn't turn on at all?), but the Lynx was still defective.

 

I then purchased and replaced Q13 with a replacement 2N3906 transistor. After this change, I got my power control back again, but the voltage was still far too high at ~7.7V. This was lower than other folks on here have reported when encountering fried zeners but I figured the McWill mod may have been loading it down a bit with it's regulator. Since I didn't find any shorts, I attributed this to another bad zener diode... I depoped the zener and threw it in my GM328 device tester and, yep, it was completely open. This was, of course, a replacement 1N5229B zener from a Console5 kit so I was amazed to see it died again! Surprisingly, I found that Mouser has the correct OEM-spec 1N5991B zeners in stock currently and bought a few. (Get them while they're hot!)

 

Once that was done, the console powered up and has been working fine for hours to my surprise. It works perfectly even after running for a while at such a high voltage, the screen was just a mess if colored blocks! I'm very lucky.

 

tl;dr The entire power supply on my Lynx 1 failed even though it was already refurbished.

 

Oh, a side note... I left in the lower resistance R56 to test my theory that the McWill display and flash cart are drawing more power (or causing unusual ripple in the power supply) that may be loading the power supply down more than usual. By increasing the voltage slightly above factory levels, hopefully current thru the supply will decrease, leading to lower strain (although with a tad more heat generation as a side effect). So far so good?

Edited by Sega CD

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Thank you for updating, I'm sure it will help someone in the future!

Odd that the zenner failed so soon after replacement, but you are luck that failure and the resulting increased voltage into the custom CPU's didn't kill one or both of em.

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