Atari 7800 Won't Turn On

[Slate]

I got a Atari 7800 a year ago, The last time i tried it it didn't turn on. Any way to fix this problem? It is Not the ac, I tried the AC with another 7800, and it worked Excellent.

[Mitch]

Does the LED next to the power switch come on? If not, then there's a good chance it's the voltage regulator.

Mitch

[FABombjoy]

Since the 7800 uses a soft power on, it may also be the 4013 flip flop.

Check that the regulator is receiving power by measuring the difference between the center and left pin. This should toggle between 0 and 9V when pressing the power button repeatedly. If so, bad regulator. If you see no change, there is a problem before the regulator, possibly the 4013.

The 5200 uses a similar arrangement, and I've see bad 4013s in 5200s before.

[Slate]

Thanks!

[Slate]

Looks like a diode overheated. Thanks!

[FABombjoy]

Out of curiousity, which one?

I'm guessing... the pre-regulator zener?

[Slate]

The diode was at the Top Right corner of the circut board, Near the power input. I think the diode was brown..

I hope this is the only problem with it.

Thanks.

[bookpile]

I have the same problem? Here's what I got when comparing the working console to a broken one. Any ideas?


Working console- Voltage Regultor.

When turned off- both sides- 0 volts
When turned on- one side- 10.6 volts- other side 5 volts

Broken console- Voltage Regulator
When turned off- one side has 0 volts, the other side has 3.4 volts-wtf?
when turned on-nothing

any ideas?

[FABombjoy]

Does the power LED actually come on for the broken console? Are you testing with the same power supply too?

Just to be sure, you're measuring 0v on the regulator's input, and 3.4v on the output? If you know that you have a good power supply & the board is receiving that power, it's probably something pre-regulator. Check the voltage on the 4013, that'll tell you if the pre-reg stage is producing proper power.

[bookpile]

First off, I appreciate your help, 2nd I don't know a whole lot about what I'm doing here, so bear with me.

I am testing with the same power supply.

The led does not come on.

Actually I'm getting the 3 volts on the input side, on the side that I get the 10.6 on on the working console.

I checked the switch, I get 5 volts and it cycles to zero briefly when I press the switch, just like it does on the working console, so I'm assuming that's good.

[bookpile]

I just plugged in my second non working 7800, and the black rectangular transistor right by the power plug heats up super fast. It's labeled MJE210.

I checked the readings on both non working systems, neither of them match the readings on the working one.

Also the second system isn't getting the voltage to the power switch.

[Slate]

What turned out to be wrong with mine was that a diode overheated, And the power button was not working. I got a new power switch installed, though.

[FABombjoy]

Actually I'm getting the 3 volts on the input side, on the side that I get the 10.6 on on the working console.

OK, that makes a little more sense.

Perform the following checks:

Measure voltage at pin 1 of the 4013 chip. This should toggle between ~5 and 0 when the power button is pressed.

If not, and there is 5V present on pin 14, then the 4013 is probably defective.

If so, the problem is probably either that MJE210 or the 2n3904 that feeds the base of the MJE transistor. These transistors act to switch the input voltage to the 7805 on and off, and if something was wrong with them it could cause the abnormally low input voltage on the 7805.

Schematic, for reference: http://www.atariage.com/7800/archives/schematics_ntsc/Schematic_7800_NTSC_UL_Low.html

[bookpile]

Well the 2nd system that was heating up is now working. It is actually my neighbors, he brought it over today, he's been bugging me to fix it ever since I moved in. The power wires were reversed on the cord. Someone had changed them. Amazingly I switched them and it works perfectly.

I tested my system and the power switch cycles from 5 to 0 when you hit the switch. But that transistor by the power input is putting out the wrong voltages. On the working one you have 10v going in and 10v going to the input on the voltage regulator. But on the non working one, you have 10v going in and only 3v going out. I think that's probably the bad part. Do you think so too? Anyone sell those? I was at radio shack today and didn't see any.