1st gen Atari Lynx had power, but no more!

[RallyMK1]

Hey guys, I know there are a lot of posts about power issues with the Atari Lynx, so I apologize for making another one.
Anyway!
I have a 1st gen Lynx that initially did not power on. I did a cap kit, cleaned the edge connector, and got it to power on no problem. 
I didn't touch it for about a week. When I got back to it, it was no longer powering on. 
I ran a 5v connection directly to C23, and confirmed the system still works, but the power buttons do nothing. 
I cleaned the contacts, no change. 
I ordered the power stage rebuild kit from console5, and replaced Q11, Q13, Q4, ZD1 and R56. Still, the power buttons did nothing. 
After re-checking my work, I found that I had C25, down at the bottom of the board, installed backwards. I removed it, tested it, confirmed it was ok, and reinstalled it correctly.

Still, power buttons do nothing, but I can confirm the system is able to power on if the legs are shorted on Q11. 
What should I test and replace next?

 

Thanks for any help in advance!

[+-^CrossBow^-]

My next guess is U6, but search the forums as there is information on additional things to check in helping to determine if that is the path to go down next.

[RallyMK1]

Thanks, from what I read, that might be the next step. I've gotta figure out if that backwards cap wrecked anything. 

[+Stephen Moss]

On 1/13/2023 at 7:41 PM, RallyMK1 said:

I didn't touch it for about a week. When I got back to it, it was no longer powering on. 

Sounds like it could be a bad solder joint or other connection issue to me, it happened to make before but a change ambient temperature or subsequently doing the screws up a little tighter results in PCB movement and suddenly no connection. If you removed the front panel flex circuits from their connector ensure that that were re-inserted correctly. 

 

On 1/13/2023 at 7:41 PM, RallyMK1 said:

I ordered the power stage rebuild kit from console5, and replaced Q11, Q13, Q4, ZD1 and R56. Still, the power buttons did nothing.

Why?

You had no solid evidence to indicate that the issue lied there, find the fault first then fix it, trying to do it the other way around can end up creating additional problems to solve.

The fact that it still does not work afterwards could mean that there was nothing wrong with it to start with or that you did a bad job of it, or potentially both in which case you would have created an additional problem to solve on top of the original fault. 

Every time you rework a PCB you risk causing damage such as broken/lifted tracks and pads, particularly if you are not very good at soldering/de-soldering, so best not to do anything unless it is absolute necessary. 

 

On 1/13/2023 at 7:41 PM, RallyMK1 said:

Still, power buttons do nothing, but I can confirm the system is able to power on if the legs are shorted on Q11. 

  

That works but that/the headphone GND hack are unwise as it results in parts of the circuit that should be running at 5V running at 9V, which can potentially cause damage due to doubling the power dissipation in some components.

Next time connect a 5V source across C39 or C50 (C41 & C40 respectively, Lynx 2) instead, something you might have known had you taken the time to read other posts on the subject first. Just double check you have the polarity correct before switching on, for the 470uF C39 (C41 Lynx 2)the positive terminal is usually marked on the PCB and the negative terminal is usually marked on the case of the capacitor

 

As Crossbow said read the other posts on the subject, the answer you need is likely to already be there.

[RallyMK1]

This was an updated I posted, but it never got approved by a mod:
The power button conductive pad is no longer conductive? Testing continuity from the button traces, I get a beep at both TP17 and TP18, so the contacts on the board make it that far at least. If I press the actual power button, there's no continuity between TP17 and TP18. If I use the pad from a known working button, I get continuity. The system still does not turn on, so there's more going on than just that rubber power button, but that sure is a weird problem. I tried cleaning it with alcohol and rubbing it across a piece of paper, but it didn't revive it. How weird. 

 

Quote

Sounds like it could be a bad solder joint or other connection issue to me (...) If you removed the front panel flex circuits from their connector ensure that that were re-inserted correctly. 

I did look for bad joints, and re-flowed a couple areas. One bad one was the DC jack, so I replaced that altogether. This is a 1st gen without the front panel flex connector.

 

Quote

Why? You had no solid evidence...

Very true. It was a shotgun approach that I should have waited on. 

 

Quote

Next time connect a 5V source across C39 or C50 instead

I'll try that today. I've got a USB wall plug that I'll wire up and report back on. 

 

I did read through previous posts, but a lot of them cover the 2nd generation, and while I'm good a soldering, I'm bad at reading schematics, so it's all a learning process. This guy still powers on when I apply the USB 5v power to C23, so I'm hopeful I can get it up and running again. 
 

Thanks for the help on this. 

[+Stephen Moss]

On 1/16/2023 at 5:24 PM, RallyMK1 said:

I did read through previous posts, but a lot of them cover the 2nd generation, and while I'm good a soldering, I'm bad at reading schematics, so it's all a learning process. This guy still powers on when I apply the USB 5v power to C23, so I'm hopeful I can get it up and running again. 

I don't always do it but I try to remember to add component reference for both the Lynx 1 and 2 to both in my replies where they differ between units, I have not gone through the entire schematic but as far as I can tell the only differences are that where the Lynx 1 has Mikey which outputs mono audio with a mono audio circuit, the Lynx 2 has Hayato which outputs stereo audio and so has a a corresponding stereo audio circuit. I believe everything else is the same, certainly the power stage circuits are identical.

 

When you say "powers on" when 5V is applied to C23 are you certain i.e. do cartridges run? As far as I can tell C23 is part of the circuit that provides power the the display so the display may do something but I cannot see how that would feed back through to power anything else. As I said power C39 (C41 Lynx 2) with 5V if the problem lies with the power stage then Lynx should work correctly and run whatever game cartridge is inserted games as normal.

If it passes that test and you have steady hands then go back to supplying the Lynx from Batteries/and external power unit and use something conductive like a paper clip or other thin piece of wire to connect Pin 11 of U6 to Pin 14 of U6 (Turn On) and Pin 7 of U6 (turn Off) for about a second to see of that turn the Lynx On and Off turn and whether or not the set On and Off state persists when you remove the connection, try no to short/connect to adjacent pins.  

[RallyMK1]

Quote

When you say "powers on" when 5V is applied to C23 are you certain i.e. do cartridges run?

Yes, with a cart in the slot it boots to the game when I have the USB 5V connected directly to C39. 

 

With batteries (confirmed working) inserted, if I short Pin 11 to 14 on U6 like this:

7   6   5  4   3  2  1
|                        C

8 9 10 11 12 13 14

            |_______|

 

Nothing happens at all. 

[+Stephen Moss]

Assuming your drawing is wrong as it shows 11t o13 it could be an issue with the On/Off latch U6 because if done correctly that should toggle the Lynx On and Off.

Check the voltage across pins 7 & 14 of U6, should be approximately 9V (on) or 12-14V (off).

 

If that is OK then check Lynx Off...

10 = 9 - 14V

11 = 0V

12 = 0V

13 = 9 - 14V

 

If you correctly short pins 11 & 14 for a second or two they should change to...

10 = 0V

11 = 9 - 14V

12 = 9 - 14V

13 = 0V

 

 

[RallyMK1]

Quote

Assuming your drawing is wrong

It must be displaying differently in a different browser. In chrome, I have it drawn going from 11 to 14. 

On to the testing:

Batteries in, not turned on
7 to 14 = 8.48V

 

10 = 8.48V

11 = 1.1mV

12 =  1.1mV

13= 8.39V

Then, shorting 11-14 to turn it on still does not do anything. 

[+Stephen Moss]

Well if none of those voltages are changing then to my mind there are only few possibilities remaining...

1. C83? (C38 Lynx 2) is shorted to ground preventing pin 11 being pulled high, try measuring the resistance between U6 pins 11 and 7(GND) of U6
2. A bad connection to pin 11 of U6, you could try re-soldering it, perhaps do pins 10 to 13 just while you are there. 
3. U6 is faulty.

Item 1 seems the less likely option as there probably would have been a small spark as you would have been effectively shorting out the batteries if that were the case, but check it anyway.

[RallyMK1]

Sorry it took me so long to get back to this. Work has been busy. 
I have replaced the conductive pad on the ON and OFF buttons, so if I hold ON, I get continuity between TP17 and TP18. 

U6 7-11 = 100kΩ

 

I think it may be that U6 has failed, possibly due to my backwards cap install. I'll get that ordered and see where that gets me.

 

[RallyMK1]

New U6 chips came in today. 

After removing the old one, I found that the pads looked awfully corroded on the left hand side.

Once that was polished up and I confirmed continuity, I soldered on the new U6, and voila! We have a fully working Lynx again. 

Thanks for the help with narrowing down the offending part. I learned a lot of lessons in the process, and I'll be sure to be less of a shotgun repair tech in the future. 

[+-^CrossBow^-]

👍