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cowdog360

How To: Installing 5V Regulator Mod in an Atari Lynx II

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So I decided to document the Lynx II 5V regulator mod because a lot of people have done it, but a lot of the documentation is in german.

 

Background: This is how to install a 5V Regulator or DC-DC converter into your Lynx II to improve the 5V regulation. The original parts are prone to failure and aren't a great design in this day in age. When the original parts fail, the regulation circuitry fails and pumps 9V into the rest of the circuitry - not good. The original 5V mod called for a LM7805 regular which runs hot and there are a lot better options.

 

What you need to do this mod:

 

5V Regulator: A 1.0amp or better 5V DC-DC converter module. You can use various diferent regulators, but I chose a Recom R-785.0-1.0. You can get these at digikey (http://www.digikey.com/product-detail/en/R-785.0-1.0/945-1038-ND/2256218%20or%20Mouser%C2%A0http://www.mouser.com/ProductDetail/RECOM-Power/R-7850-10/?qs=YWgezujkI1LK5NzKL%2Fc9sg%3D%3D) or Mouser (http://www.mouser.com/ProductDetail/RECOM-Power/R-7850-10/?qs=YWgezujkI1LK5NzKL%2Fc9sg%3D%3D)

 

Diode: You'll need a diode as reverse voltage protection, but you can re-use one you remove, or replace it with something modern like a 1N4001.

 

Tools: You will need a soldering iron, a desoldering iron (or pump, or solder wick, etc), a hobbyist knife/scapel, hot glue gun. Of course you'll need solder and hot glue.

 

Wires: Some small gauge wires, I used pieces from a CAT5 ethernet cable.

 

First off, you'll want to make sure you have a 5V converter, like the RECOM. It's a 3 terminal device. On the left, terminal 1 is Voltage Input, the middle is ground, and the right is 5V output.

IMG_0038_zpsmvfqgfiy.jpg

 

Open up your Lynx, and take out the logic board. You will want to examine it right near the Brightness Knob and AC power jack. There are 3 sections of parts you are going to remove from the board, they are highlighted in red. You're going to be removing D9, D11, D13, Q8 (near TP18), and the inductor coil below L14.

IMG_0041_zpssyhoxo4r.jpg

 

To remove these parts, I just used my soldering iron, some fine tweezers and the hobby knife to pry them up as I heated up each component. The inductor will have to be desoldered from the bottom of the board (it has 4 pads). You're going to want to save one of those big diodes for reuse.

IMG_0044_zpsf7fnrkk8.jpg

 

Flip the board over so the the battery terminals are facing up. You want to find the large solder pad right below the top leftmost pad on the board.

IMG_0047_zpsh3e7srby.jpg

 

Now comes the fun part. You need to sever the trace from the board heading to the pad with your knife. If you look very closely you can see the trace in the board (it's green and tough to spot). Dig in good with your knife. It will look like this when done:

IMG_0048_zpswaqmnrpb.jpg

 

Flip the board back over. Now you'll need to install a jumper wire in the top two pads where the inductor was, and a diode in the lower two pads. For the jumper, just use some copper wire or a lead of of some other component (like a resistor or old LED). For the diode, you'll have to put some solder down on those pads to plug up the holes. Very carefully hold the diode in place and solder it in. Make sure that the black stripe is facing to the right. If you reverse this, things will not work.

IMG_0049_zps7lw1h7m1.jpg

 

Now, take some of those wires, and you're going to need to solder them to 3 of the 4 diode pads you removed. I've marked this diagram in colors VIN, GND, and VOUT. I used a yellow wire for VIN, a black for GND, and red for VOUT.

Voltage_zpsl3lb8ofg.jpg

 

Now flip the board over and grab your regulator module. You will need to also have a short section of wire to run from the upper left pad near the cut you made to the VIN (left) terminal on the regulator. The regulator will actually have two wires soldered to VIN. You of course then solder up GND to the middle and VOUT to the right. Secure everything with some hot glue and it should look like this:

IMG_0053_zps8dclhbrf.jpg

 

Here's a look at what it all looks like done. This Lynx also has the McWill LCD mod which is why you see the other wires:

IMG_0054_zpsvmekqtec.jpg

 

IMG_0055_zpshb26utfy.jpg

 

Power it up and test. If it doesn't work, check all your connections and double check that trace cut to make sure it was good.

 

I'll probably add more to this as I experiment a bit more.

Edited by cowdog360
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No problem, just thought I'd give back a little. Now I'll also mention that some other people and the German site mention using a LD1117S50TR regulator which is SMD, smaller and a lot cheaper (about $.50 instead of $7). The issue that I've read is that it outputs a max of .8A, whereas the other regulators are good for 1A. That might cause some issues with the McWill LCD if the regulator is undersized, which is why I went with the Recom.

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As said before:

 

DO NOT PUT THAT LD1117S50TR LINEAR REGULATOR IN YOUR LYNX

 

It will not work since it will overheat.

Some quick calculation:

 

Input voltage Uin=9V and the output voltage Uout= 5V

Let's say the 5V load Il = 500mA and i think that's even a bit conservative.

The power that needs to be dissipated by the linear regulator = (9V-5V)*500mA =2W

The amount of heat that will be generated is specified by the thermal resistance in the datasheet.

For the SOT-223 package this is 110°C/W

So the total amount of heat-up = 110°C*2W = 220°C

 

Since the maximum junction temperature = 125°C it should be clear that this is never going to work (for a long time)

 

If I'm not mistaking someone here tried it before and was complaining that his Lynx was always resetting.

That's because the regulator always goes into thermal protection until it cools down and outputs again in an never ending cycle.

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Lynx with the new LCD tops out at about 0.3A which is well below LD1117's max limit but the voltage different is the problem. I've tried it and I couldn't use it so I went with a switching regulator instead.

 

LD1117 series is meant to be used with Lipo batteries, not as a full voltage regulator

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Holy cow. I was just looking into this as I bought mcWills lcd mod. The instructions sucked so I was gonna pass but this is awesome!

Crap, I already did the mcWills mod (just finished in fact). What are the odds that I'll kill it if I try the regulator mod? Lol

And I need the upgraded speaker and a new front cover and....($10000000 later and she's finished!)

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Holy cow. I was just looking into this as I bought mcWills lcd mod. The instructions sucked so I was gonna pass but this is awesome!

Crap, I already did the mcWills mod (just finished in fact). What are the odds that I'll kill it if I try the regulator mod? Lol

And I need the upgraded speaker and a new front cover and....($10000000 later and she's finished!)

I did McWill's LCD on both Lynx's and went back afterwards to do both the 5V regulator and a Q12 replacement. Probably not a bad idea to replace Q12 while you're in there.. it's $1.

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I initially came to this forum specifically for McWill's LCD mod, but noticed talk about a regulator mod. I was completely confused and intrigued by everything I read till now! Thanks cowdog360 for making things clearer.

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I did McWill's LCD on both Lynx's and went back afterwards to do both the 5V regulator and a Q12 replacement. Probably not a bad idea to replace Q12 while you're in there.. it's $1.

 

Which part do you recommend for replacing Q12? Sometimes trying to sort thru Jameco and Digikey is almost as bad as browsing Bests website :P

 

 

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I drew in red line where to cut it, just dig in through with sharp knife and using magnifying glass to make sure you did cut through and deep. If you have a multimeter, set it to ohms, low range (like 100 ohms or less) and put probes on the 2 large solder spots I indicated with arrows. If it shows 0 or a few ohms, you need to work on cutting a bit more. If it is open, it should be set.

 

For running a wire to the new regulator, I used component side (other side from your picture) and soldered directly on the battery + leg on the PCB and ran the wire across to the location of new regulator. Keeps the back side clean and neat. :D

 

http://i.imgur.com/VBgNuaW.jpg

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Firstly I'd like to thank cowdog360 for taking the time in putting together this most excellent post of which I will be undertaking this weekend (hopefully).

 

I've just got a quick question.....

 

The diode that is used for the reverse voltage protection, does this just short out the supply if a reverse voltage is applied or does the current flow through the diode to the rest of the Lynx.

 

Thanks again for all your help. :-)

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Right I've gone and had a good look at the schematic and the Lynx 2 board. The diode mentioned above for reverse voltage protection, the current flows through this from the power supply.

 

The "inductor coil below L14" is actually L14. You could keep this in place and instead run a diode (or a schottky diode for less forward voltage loss) in line with the connection from the output of D9 (labelled VIN above) to the input of the power reg. It's one less part to remove plus you get the benefit of the inductor coil smoothing any ripple in the power from the power supply.

 

Also looking at the schematic you could leave the D11 diode in place and solder the "GND" and "VOUT" wires directly to it. This is a diode straight across the power rail so that it will short any reverse voltage that may be present.

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Hi, I'm new here :) I got an Atari Lynx recently and decided to perform this mod to be sure it works well for many more years.

 

It all worked well apart from I notice something weird. My Power LED flashes when I use batteries, but not the very first time I turn it on, only the second time and every time thereafter. If I pull the batteries and wait a minute then install again, the same happens. First power on is fine, but thereafter the light constantly flashes.

 

I use rechargeable Eneloop batts which have been fine before the mod and have been checked to be fully charged. I even tried with a second set I had and some Non Rechargeable Alkaline Types and got the same issues. If I turn the screen off for a second then back on the problem goes away, so I can stop it, but its a little bother that i'd like to fix if its possible...

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The flasher circuit warns us when the battery level is a little low. Rechargeable batteries typically tops out at 7.2v for 6 packs AA, below the normal 9v for non-rechargeables.

 

I've scanned and posted schematic of Lynx II a couple months back, and I'll copy the relevant section:

ddAb8Zc.png

 

The line on top right goes to connector that connects to LED on the membrane. I am not sure which part sets the "low voltage" threshold. With the new 5v mod, one would think Lynx 2 can do OK as low as 6.5v so if someone knows what resistor to change, I'm sure many of us blinker-hater would love it.

 

A more hard fix would be to remove transistor Q11 and wire straight through to ground, it will be steady only.

Edited by 7800fan
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I have this problem with regular alkaline batts as well. I don't have a psu to test if it does the same when plugged in. Turning the screen off then back on again momentarily fixes the problem, but after some time it starts again.

 

It must be something to do with a resistor somewhere as you said 7800fan. I thought Q11 controlled the power button, without it would the lynx not turn on or off properly? If anyone knows which resistor is controlling the flasher circuit and what might be a better value, that would be great.

 

Does anyone else have this issue after performing the mod?

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It should not happen if you have a clean 5V signal.
S-8054 is reponsible for the voltage detection. Don't know what voltage it triggers on since the exact submodel is not specified on the schematic and never seen the exact part model referenced anywhere.
Measure the 5V with a meter. My guess is its below 5V

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I have this problem with regular alkaline batts as well. I don't have a psu to test if it does the same when plugged in. Turning the screen off then back on again momentarily fixes the problem, but after some time it starts again.

It must be something to do with a resistor somewhere as you said 7800fan. I thought Q11 controlled the power button, without it would the lynx not turn on or off properly? If anyone knows which resistor is controlling the flasher circuit and what might be a better value, that would be great.

Does anyone else have this issue after performing the mod?

Did you use a linear voltage regulator?

The circuit in the schematic is both a low voltage detector and a ripple detector.

It would not surprise me that your linear regulator is overheating. This in turn causes a voltage ripple because it the regulator is going into protection mode.

Switching off the lcd causes a lower current draw which in turn cools down the regulator fixing the problem temporarily.

Previously in this thread I advised against replacing the original switching power supply by a linear one.

Edited by StijnDW

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The 5 volt line coming from the recom Regulator is measuring a steady 4.99V. The eneloop batts are at 7.63V, the regular alkaline batts at 8.92V.

 

Very weird then, it should not happen. Something triggers the AC detection circuit. Maybe some HF component on the DC line generated by the switching regulator.

Bit harder to analyse.

For all it mathers it could also be the LED itself

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