7800 suddenly won't turn on

[shear_xear]

Hi everyone. I have a 7800 that powered on yesterday, but not today. I replaced the power regulator, swapped out the power jack, the large capacitor next to the power jack, put on a new power button, tried multiple power adapters that are known to work, and swapped out the MJE210 (transistor?). Still nothing. The old MJE210 started smoking at one point, if the tells you anything. I have a multimeter, but have never been able to figure out which setting it needs to be on when taking readings, Any help would be greatly appreciated. Thanks!

[+DrVenkman]

Quick question: why did you do all that work on the machine before trying to diagnose what's going on with it first? If the transistor was smoking, was that before or after you started performing surgery on the board?

 

I *strongly* suggest you spend a little while on Youtube watching videos to learn how to use your multimeter for basic stuff like continuity testing, measuring DC voltage, and measuring resistance. Then you can figure out what's wrong with your 7800.

[7800fan]

Did you make sure the 7800 adapter was plugged in and the AC outlet is on if it's switched? Also a couple of 7800 I've had, they had problem with power switch button not working. Those button gets worn out and may need to be replaced.

[+Stephen Moss]

This thread may help you diagnose the problem.

[shear_xear]

The button was replaced and the power adapter was plugged in. I will check out the thread, thanks!

[tep392]

Double check all your power adapters with the voltmeter before doing any more testing. If the original power adapter failed and smoked a component in your 7800, then it subsequently might not have worked with the known good adapters. Don't assume the original adapter is good. You will want to toss that adapter if it's bad.

 

I don't mean this to sound insulting, but if you don't know how to use a multi-meter, then you probably aren't qualified to fix the console. You might just want to find someone who can fix it for you.

 

Good luck.

[shear_xear]

I have looked at videoes on how to use the multimeter, but have yet to fine any that don't skip over the very basics of how to use it. I have fixed about ten 7800's in the past without one, but I know that it would be invaluable to be able to use it. The power adapter that I use has worked perfectly for almost two years without causing any sort of smoke to occur. I'm actually using it now and everything is working perfectly on a different 7800.

[tep392]

Checking power supply voltage is always the first step when a console stops working. You lucked out that it wasn't the PS when you decided to plug it into another console. Does it really matter that it has worked for two years? It's 30 years old.

 

If you look at the 7800 schematic, available on AA, you can study the power switch circuit and if you understand how it works, check some voltages to verify each component is doing what it's supposed to. Start at the power supply and work your way through the circuit until you find the culprit. You should be able to check a lot with just a voltmeter.

[shear_xear]

Okay. Will do. I have used the meter before, but the dial was turned and I turned it to what I thought the correct setting is (20 dcv). I actually tested the 7800 with a brand new Atari Guide 7800 adapter and the older adapter and got 10.1v off of both when it was off. I will look for the atariage guide and try to find the issue. Thanks a lot!

[tep392]

Check the output of the voltage regulator gives you 5V and that it switches on and off with the power button. If it doesn't, then you know the problem is in the power circuit. There is a flip flop, CD4013B, in the upper right corner of the board that switches states as you press the power button. You should see pin 1 change from 0V to 5V and back as you repeatedly press the power button. Look at the voltages on your good console for comparison.