Safe Boot (Atari Lynx II)
If you have a possibly faulty Lynx II, due to how the power regulation circuit is designed (poorly) I would highly recommend the first thing you do is NOT plug it into batteries or power.
If the diode D13 fails, the R74 resistor is out of spec, Q12 internally shorts or many other simple failures on the power board, the entire system can receive over 9V, destroying the Suzy first usually.
Instead, I would recommend safely applying 5V to the system by bypassing the entire power circuit as mentioned in the Power Circuit article before this.
In short, use a bench power supply to apply ground to the metal shield solder point or shield itself, and 5V (not 9V!).
This should first boot your system up fully and if that works you will see the screen, game and audio all fully working. If you have a short you will see excessive power draw over 500mA and you need to fix that first.
Confirming Power On
With the basic power rail checked by injecting 5V, it is time to go back to the battery springs and connect your bench power supply to it.
๏ปฟRemove the speaker, front board, screen and game from the motherboard so it is just the motherboard.๏ปฟ
First short pins 31 and 33 of the cartridge slot together to power up the U6 hex inverters and allow power up testing without a game (as you could destroy the game if it is over-voltage).
With your bench power supply set to 5.5V (so 500mV more than before), and connected to the battery springs (ground probe on battery spring ground, positive probe on battery positive), get some tweezers short over TP17 and TP18 (or pin 6 and 7 of the front ribbon connector).
This should power your system up and you should see around 100mA power draw with nothing else connected to the motherboard.
If you do not, you need to fix your power circuit, go back and read the Power Circuit article.
Confirming 5V Regulation
Presuming you get the power draw as mentioned, it is time to measure the system voltage that all components on the motherboard will be receiving to confirm if the circuit regulation is working.
Using your multimeter in Voltage DC mode, put your black probe on the metal sheild ground, or the solder pad of the shield, and the red probe on the positive battery spring (where your bench power supply is currently connected).
You should measure 4.8V to 5V. If you see the full 5.5V that your bench is outputting, your system is very unsafe to power on and do not proceed until you find the issue.
The usual issue with failed regulation is the D13 diode is dead, R74 is not 130R, or Q12 is shorted. See this video on basic diagnostics and fixing that circuit, or the Power Circuit video link in the previous article.
If you do see 4.8V to 5V from the measurement, increase your bench power supply to 5.7V, then 6V, then then finally 9V, watching for the 4.8V to 5V measurement making sure it never increases.
If it does increase, stop and go back down until you find the fault on the power circuit.
Only once these steps are done should you connect the speaker, screen and game back to the system.
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