What are the 5v regulator mod?

[Mojado]

The actual regulating is done further down the chain, at zener diode. It's supposed to dump excess voltage to ground while maintaining 5v across the spot. (seems like inefficient design BTW unless I misread schematic) If the diode or resistor failed, you won't get 5v regulation.

 

I'm almost afraid to ask, does your Lynx still work with 6v power? If so, you're lucky. Many component usually fries easily when you dump 9v due to failed volt regulator.

I've been looking at this for a bit. . .the original schematic is not a linear regulator but rather a switching regulator. The 100uH inductor with the FET to its left, plus the diode, make for a switching regulator. I honestly don't see the need for this mod.

[Mojado]

Those are actually really good questions. I just wrote up a how-to for people who wanted to do it. However, the last few Lynx's I've stopped doing the regulator mod on, and just replace the D13 zener with a newer one just for reliability.

 

The main issue is that when the zener goes, the regulation fails and then you get 9V into the rest of the Lynx. So the modern 5V regulator is something people are doing for safety. What I've seen though with the way this mod is done is that the DC-DC converters draw power even when off, so the batteries drain out pretty quick compared to the original circuitry.

 

Ideally, I'd just keep the original circuitry and the best thing to do would be to develop a crowbar circuit to catch things if the voltage pops over 5V.

 

I'll have to sit down and really look at the circuit to answer the other questions you have.

Does anyone know what the "Color" pin does on the Mikey IC? That's where the "ac connected" pin goes. 0 volts when on batteries, 4-ish volts when on AC power.

 

The original power circuitry has a pretty nifty switching regulator. Don't know why folks are gutting it and putting another regulator that, as you pointed out, is on all the time whereas the original switching one is only on when the Lynx is on. Does the new regulator have over-voltage protection?

Edited May 30, 2016 by Mojado

[Mojado]

I know you're super happy with your power mod and its 1000 times better than zenor diodes. If you ever do another Lynx, try the switching voltage regulator I have shown above. You'll be pleasantly surprised by its performance.

Zener diode is only used as a voltage set point. Original atari lynx has a switching regulator. If you scoped Vgs on the FET next to the 100uH inductor, you'd see it switching.

Edited May 30, 2016 by Mojado

[bdoi]

@ cowdog360

I am about to do this mod. Do you don't advice me to do this mod?

 

thanks

[leonk]

I cant comment on original lynx as ive only been working on the newer model 2. But based on my experience of fixing a dozen of these and the leaked schematics found on console5, it does not have a switching regulator.

 

What PSU are you using to power your lynx when you measured? original AC to DC Atari Lynx transformer, or modern 3rd party switching PSU?? Your scope migjt be confused by your power source.

[Mojado]

I cant comment on original lynx as ive only been working on the newer model 2. But based on my experience of fixing a dozen of these and the leaked schematics found on console5, it does not have a switching regulator.

 

What PSU are you using to power your lynx when you measured? original AC to DC Atari Lynx transformer, or modern 3rd party switching PSU?? Your scope migjt be confused by your power source.

Can you link me the console 5 schematics, please?

[leonk]

Google is your friend.

 

http://console5.com/wiki/Atari_Lynx

[cowdog360]

@ cowdog360

I am about to do this mod. Do you don't advice me to do this mod?

 

thanks

Honestly, it is up to you. I don't know how much protection you're really adding with a new regulator, but you are for sure going to have more battery drain than stock. The main thing you may get from the regulator is if it fails, it may fail open and not cause 9V to go through the Lynx.. but I don't know exactly how those new DC-DC regulators fail.. if they fail that way.

 

Once we all get a better idea of the power circuitry on the Lynx, it will be interesting to see what we can all come up with. In the meantime, I'm just replacing the zener diodes in my Lynxes instead.

[7800fan]

AFAIK Lynx 2 uses emitter-follower design for transistor and zener diode regulation. If those fails, there's nothing to sink excess voltage and keep the 5v rail at 5v, full unregulated voltage will get dumped into all of Lynx chips and parts.

 

You could replace the transistor and zener diode now to prevent failure later or you could do the 5v mod with something that stops passing power when it fails like a basic 7805 regulator and similar switching regulator.

 

Or you could remove all those crap, install USB port, and use it with USB ports that has 1A+ output (such as phone chargers) and add in a 5v lipo charger + lipo batteries.

 

I'd love to do this one day. Good lipo can easily outlast AA's if you got large 3.6v lipo in the same space designed for 6x AA batteries.

[cowdog360]

AFAIK Lynx 2 uses emitter-follower design for transistor and zener diode regulation. If those fails, there's nothing to sink excess voltage and keep the 5v rail at 5v, full unregulated voltage will get dumped into all of Lynx chips and parts.

 

You could replace the transistor and zener diode now to prevent failure later or you could do the 5v mod with something that stops passing power when it fails like a basic 7805 regulator and similar switching regulator.

 

Or you could remove all those crap, install USB port, and use it with USB ports that has 1A+ output (such as phone chargers) and add in a 5v lipo charger + lipo batteries.

 

I'd love to do this one day. Good lipo can easily outlast AA's if you got large 3.6v lipo in the same space designed for 6x AA batteries.

Its funny that you mention the Lipo. Thats the next mod I'm looking at doing on one of my Lynxes. Use an Adafruit Powerboost 1000C with a pair of 18650 cells in series. What I'd love to do is design a 3d printed battery compartment replacement.

[Mojado]

@ cowdog360

I am about to do this mod. Do you don't advice me to do this mod?

 

thanks

 

What's your goal in doing the mod?

[Mojado]

Google is your friend.

 

http://console5.com/wiki/Atari_Lynx

 

Thanks. I didn't want to use google and risk us talking to different schematics. I didn't want to wind up doing negative work.

 

So the Lynx I and Lynx II have the same 5V regulators, and yep, they are switching regulators.

 

They use a standard buck converter, but do the switching on the bottom, as opposed to high side switching. Doing it this way they can use an n-channel FET instead of a p-channel, so their efficiency goes up. Here's the standard buck converter:

 

Here's the handjob I did on the schematics. The Lynx uses back to back round-robin inverters to latch the system's ON/OFF state.

 

So, here's how the Lynx's (I and II) switching regulator work

 

So you end up having the regulated 5V (from the switching regulator) hanging off the 9V line. You'll notice on the schematics that the 9V line is the same as the 5V line. The point where the diode and inductor meet will change from 9.7 volts and ~0V. If you measure the system's ground voltage to the battery negative (TP 16), you'll notice it reads about 4V. And if you measure Vgs on the switching FET, you'll see a square wave, indicating a switching power supply which uses the BJT/Zener to set the regulator's setpoint to 5V.

Edited May 31, 2016 by Mojado

[Mojado]

Honestly, it is up to you. I don't know how much protection you're really adding with a new regulator, but you are for sure going to have more battery drain than stock. The main thing you may get from the regulator is if it fails, it may fail open and not cause 9V to go through the Lynx.. but I don't know exactly how those new DC-DC regulators fail.. if they fail that way.

 

Once we all get a better idea of the power circuitry on the Lynx, it will be interesting to see what we can all come up with. In the meantime, I'm just replacing the zener diodes in my Lynxes instead.

 

Thoughts?http://atariage.com/forums/topic/236279-what-are-the-5v-regulator-mod/?p=3521278

 

[SwampFox56]

Wow, very cool info. Basically a buck converter (aka DC to DC step-down converter) stuck into a Lynx. Should get rid of pretty much all the heat produce by the Lynx. Thanks for sharing! :)2

[Mojado]

Wow, very cool info. Basically a buck converter (aka DC to DC step-down converter) stuck into a Lynx. Should get rid of pretty much all the heat produce by the Lynx. Thanks for sharing! :)2

Well, the mod replaces the Lynx's original regulator with a new one, but I'm seeing that the atari lynx CAME with a switching buck converter already (not an inefficient linear regulator as is asserted), so I'm saying this mod isn't necessary.

[leonk]

ok. But this still doesnt explain why it's pretty common for these units to fail. In all cases, the rail measures 9V (to the CPU!) The root cause is discovered to be a shorted zenor diode.

 

You can leave your console as is and hope that the zenor you have in your lynx doesnt short. Others simply decide to not take the chance.

[Orange-Phantom]

Funnily enough Mojado I came to the exact (or close enough) conclusions that you came up with in this earlier thread.

 

http://atariage.com/forums/topic/247305-old-stock-lynx-vs-new-mcwill-screen-recom-power-reg-power-consumption/

 

It is a high frequency switching regulator circuit, otherwise by the law of physics the excess voltage has to be dumped as heat. My voltage vs current measurements further confirm this.

 

Also I passed another one of my Lynxes to a fully qualified electronics engineer who has some 40 year plus experience, he checked over the circuit diagram and hooked it up to an oscilloscope too and yes the FET is switching.

 

The FET is the part that separates the 9v to the 5v side.

 

Further discussions with my friend said that the failure of the FET is most likely to be the source of the 9v into the Lynx. Years of it being high frequency switch can cause them to fail. He said he's repaired countless circuits such as variable speed controls etc where the FETs have slowly failed. He said there is no harm in replacing the Zener either.

 

I'm putting my Lynx back to stock as the Power Mod in my opinion as I've stated before is a backwards step. If you want to fix your Lynx new Power FET and new Zener diode (just to be sure).

Edited May 31, 2016 by Orange-Phantom

[cowdog360]

Funnily enough Mojado I came to the exact (or close enough) conclusions that you came up with in this earlier thread.

 

http://atariage.com/forums/topic/247305-old-stock-lynx-vs-new-mcwill-screen-recom-power-reg-power-consumption/

 

It is a high frequency switching regulator circuit, otherwise by the law of physics the excess voltage has to be dumped as heat. My voltage vs current measurements further confirm this.

 

Also I passed another one of my Lynxes to a fully qualified electronics engineer who has some 40 year plus experience, he checked over the circuit diagram and hooked it up to an oscilloscope too and yes the FET is switching.

 

The FET is the part that separates the 9v to the 5v side.

 

Further discussions with my friend said that the failure of the FET is most likely to be the source of the 9v into the Lynx. Years of it being high frequency switch can cause them to fail. He said he's repaired countless circuits such as variable speed controls etc where the FETs have slowly failed. He said there is no harm in replacing the Zener either.

 

I'm putting my Lynx back to stock as the Power Mod in my opinion as I've stated before is a backwards step. If you want to fix your Lynx new Power FET and new Zener diode (just to be sure).

 

I'm of the same opinion. On every Lynx I refurbish, I've been replacing the FET as standard procedure since they are about $1 US. I'm also going to just make it standard to replace the zener as well. Since these parts are pretty older and hard to find, these are the parts I've been using (Digikey part numbers):

 

Q12 MOSFET: 2SK2231TE16RQCT-ND

D13 Zener: 1N5229BFSCT-ND (this is probably the best equivalent I could find for the older zener, and works fine)

 

I'm really rusting on my EE skills, but just looking at that circuit originally it looked far too complex to be a "simple" power regulation circuit. Excellent work guys. I'll edit my 5V regulator mod post to let people know it is an option, but probably the easiest method would be just replacing that zener and FET to give you some peace of mind and maintaining the original circuitry.

[leonk]

Orange-Phantom: Your original testing was switching regular + McWill screen vs stock Lynx. Not keeping all variables the same here.

 

A better comparison would have been stock Lynx II vs Lynx II with the Recom switching regulator (I assume R-78?) and NO McWill screen! If you did this, you would have found the measurements to be pretty much the same. The R-78 brings a lot of good things to the table:

 

- 97% efficiency

- 9 - 48V input

- 3 million hours MTBF (>300 years!!)

 

The 3055E N-Channel MOSFET is a known failing component of the Lynx. I've replacement many of them. All you're doing is buying yourself another 10-15 years. Why not just fix it once, and never worry about it ever again? These consoles are only going to get more expensive with time. When 9V rushes through your Lynx CPU and your McWill LCD screen, how are you going to fix it then? (or would you even care)

[cowdog360]

Orange-Phantom: Your original testing was switching regular + McWill screen vs stock Lynx. Not keeping all variables the same here.

 

A better comparison would have been stock Lynx II vs Lynx II with the Recom switching regulator (I assume R-78?) and NO McWill screen! If you did this, you would have found the measurements to be pretty much the same. The R-78 brings a lot of good things to the table:

 

- 97% efficiency

- 9 - 48V input

- 3 million hours MTBF (>300 years!!)

 

The 3055E N-Channel MOSFET is a known failing component of the Lynx. I've replacement many of them. All you're doing is buying yourself another 10-15 years. Why not just fix it once, and never worry about it ever again? These consoles are only going to get more expensive with time. When 9V rushes through your Lynx CPU and your McWill LCD screen, how are you going to fix it then? (or would you even care)

 

I agree with the RECOM being a good choice.. but the issue is still that the way the mod is done it is causing extra power drain with the Lynx is off because the regulator never actually shuts down. It's a shame they didn't just use a standard power switch on the Lynx and instead got all fancy with soft buttons instead. I'm going to build a Lipo powered Lynx next though, using a powerboost 1000c for the charging/regulation circuitry. It will have the same issue though, drawing power at idle.

[leonk]

ah! got it. but this is true only if on batteries. On AC adapter it's a moot point.

[Mojado]

Orange-Phantom: Your original testing was switching regular + McWill screen vs stock Lynx. Not keeping all variables the same here.

 

A better comparison would have been stock Lynx II vs Lynx II with the Recom switching regulator (I assume R-78?) and NO McWill screen! If you did this, you would have found the measurements to be pretty much the same. The R-78 brings a lot of good things to the table:

 

- 97% efficiency

- 9 - 48V input

- 3 million hours MTBF (>300 years!!)

 

The 3055E N-Channel MOSFET is a known failing component of the Lynx. I've replacement many of them. All you're doing is buying yourself another 10-15 years. Why not just fix it once, and never worry about it ever again? These consoles are only going to get more expensive with time. When 9V rushes through your Lynx CPU and your McWill LCD screen, how are you going to fix it then? (or would you even care)

 

One of the first questions reliability analysts ask when coming up with an MTBF is, "What do you need the number to be?"

 

I looked at the Recom and they don't show you what's in the box. . .a little disappointed by that. Usually folks show you block diagrams of what's in there. The thing with power electronics is that it's a lot like railroad technology . . .ain't a lot of room for innovation, so the stuff from the 80s is still used today. A buck is a buck is a buck. I'm certain if you look inside the Recom you'll find a basic buck design with zeners for reference (everyone does that), a FET, inductor, diode, etc. . .except everything is packed in tightly. They have thermal shut off and overcurrent protection, but no overvoltage protection. So both Atari's and Recom are susceptible to over-voltage failures.

 

​The Recom has the same topology and same type of hardware (I'm assuming, since they don't tell you what's in their setup) and same failure modes so you don't really buy yourself anything by gutting the Lynx's power system and kludging a regulator in there that, as Cowdog points out, is on the entire time and draining your batteries.

 

The best bet, in my opinion (EE power systems guy in aerospace), is to do what Cowdog and Orange-Phantom said and just change out the power FET and zener diode with modern drop in replacements. I'd also replace the diode that's between the Power FET and the inductor (D14 on Lynx I), since that conducts load current when the FET is OFF while switching.

 

By the way, I'm calling BS on 97% efficiency. Since the load is relatively low, the parasitics are not going to be negligible when compared to the converter load. . .no way that's at 97%.

Edited June 1, 2016 by Mojado

[cowdog360]

Here's the other DC-DC converter that I've used, looks like the datasheet has more info: http://power.murata.com/data/power/oki-78sr.pdf

 

I don't see anything about overvoltage protection either. Maybe the controller chip has that implemented in it, maybe not?

[cowdog360]

@Mojado what do you think about adding an overvoltage protection circuit at the end of the power supply? I'd have to figure out where on the board to input it, but I'm thinking this could work pretty well:

http://cds.linear.com/docs/en/datasheet/436112fb.pdf

 

Then rather than changing the regulator, add this on for safety.

[leonk]

Why would overvoltage protection be an issue with these modern switching voltage regulators? They are rated at 7-36/48V! 36/48V is a lot more than any battery or AC/DC adapter can put out. Isn't the issue more with reverse polarity? But there are already diodes on the PCB to protect them from that happening.

 

The only other issue might be current.. The OKI-78SR docs say to use a 2a fuse and you should be set.