Atari 7800 is dead

[sthamann]

Hi there,

 

i have bought an old atari 7800 and i´m trying to get it back to life.

 

As far as i was initial trying to power on the console the old power supply smoke away.

 

So i have opened the case and see that the the big 2200uf capacitor was blown up.

 

When i attempt to replace the capacitor - the contact of the + pole broke out from the motherboard ;( So maybe someone know an alternative contact that i can connect to the + pole of the capacitor, to get the circuit back to work.

 

I have the pal version revision c.

 

I´m not sure if this is the only problem - so maybe i need additional help later.

 

Thank you very mutch.

 

[Andromeda Stardust]

Sorry to hear that. It may yet be possible to repair the console. Desoldering is a delicate process that takes special tools and patience. Also check for evidence of cracked or burnt ICs. If other components are fried, the console is probably toast.

 

If you can't fix it yourself, don't throw it out. Consider donating it to a fellow AAer who may be able to refurb or use it for spare parts.

Edited August 5, 2015 by stardust4ever

[sthamann]

Hi,

 

here are picture of what i have tried yet.

 

1.) This is the replaced capacitor - the problem is the contact of the + pole was broken out while replacing the old capacitor.

I have tried to connect the + pole to resistor 3 and later 4 - without success, so at the moment i don´t know if the problem is the wrong / missing connection of the + pole or if
additional other parts are defect - so i want to fix this problem first and check then for maybe other issues

 

2.) I have replaced the defect power supply with a new one (9v dc 1a)

 

3.) At the power regulator i get a constant ~ 3,5 V in the in (what should be at least 9 v i guess) and ~ 0,6 v at the output - independly if i pressed the power switch or not

 

[WakeyTiger]

I'd love your cartridge port surround if this is broken/unrepairable... the one fixed to the PCB with screws, as mine has just broken!

 

I'm in the UK, but totally understand if you don't want to sell

 

Good luck!

 

Matt.

[+Stephen Moss]

@ sthamann

When you mentioned the 2200uF capacitor I assume you are referring to the one in the 7800 and not in the power supply as this was not entirely clear in your original post.

 

If so and you can see the track that the pad for the capacitors +ve terminal was connected to just put the lead through the original hole, bend it as require and solder it directly to the track (you will have to scrape off the solder resist with a craft knife first).

If the pad was in the middle of the track you may have to bridge the gap between the two sections, you can use the excess material cut off from the capacitor leg for this or a piece of wire.

 

In your second post you say you tried to connect the +ve connection of the capacitor to Resistor 3 and then 4, I hope you meant R53 and R54 as connecting to R3 and R4 would not be helpful.

 

I am not certain what is normal for the 7800 however, from the circuit diagram I would not expect to see any voltage at the input to the regulator with the unit in its off state.

Hopefully the 4013 is in a socket otherwise another approach may be required, if it is in a socket your should remove it first noting its orientation ("top" end indicted by a semi-circular notch and/ or circular indent) so that you do not put it back the wrong way round. Then insert a piece of wire (preferably solid, i.e. cut off capacitor leg) in the socket with one end at pin 1 (top left in regard to the aforementioned notch/indent) and pin 7 (bottom left in regard to the aforementioned notch/indent).

 

Now with the capacitor replaced and 4013 removed as above check the voltage at the input and output of the regulator, across the 200uF capacitor and if you can locate it measure the voltage drop across R53.

If all components/circuits are functions correctly I would expect to find...

Approximately 0 volts DC at the input and output of the regulator

Approximately 9 volts DC across the Capacitor and

Approximately 4 Volts DC across R53.

 

If that all checks out remove the link from the IC socket, reinsert the 4013 and see what happens.

 

As you have already had one power unit go up in smoke I would suggest pre-connect the leads of the DVM for the measurement to be made and have another party present to turn the power to your power unit on and off just long enough to make the measurement incase a fault still exists that could damage your new power unit.