Bum 7800? Need troubleshooting help.

[Rex Dart]

Hi there...

I bought this used 7800 off ebay, and I've never owned one before, but it seems to have a few issues. First, the picture from 2600 games is very dark. A few are bright enough to play (and may be working as intended), but Space Invaders, Midnight Magic, and others are just way too dark to play. Also, the audio doesn't come on until the system's been running for a couple of minutes. I have to play in silence until the sound pops in. If I turn the system off to swap carts, then it's another several-minute wait. It's hooked up to the TV via an RF switchbox, but with nothing else connected to the switchbox. Would connecting it directly to the TV help (I don't own the adapter currently) with the picture, at least? What about the audio? What can I check out on the motherboard to troubleshoot this?

 

Thanks!

[Toraborakid]

Hi there...

I bought this used 7800 off ebay, and I've never owned one before, but it seems to have a few issues. First, the picture from 2600 games is very dark. A few are bright enough to play (and may be working as intended), but Space Invaders, Midnight Magic, and others are just way too dark to play. Also, the audio doesn't come on until the system's been running for a couple of minutes. I have to play in silence until the sound pops in. If I turn the system off to swap carts, then it's another several-minute wait. It's hooked up to the TV via an RF switchbox, but with nothing else connected to the switchbox. Would connecting it directly to the TV help (I don't own the adapter currently) with the picture, at least? What about the audio? What can I check out on the motherboard to troubleshoot this?

 

Thanks!

 

Well first off congrats on being a 7800 owner, with that being said, i am wondering of u cleaned the pins in the cart slot fist of all, and 2nd the audio might be a problem with a loose solder joint/joints.

 

as for the video u might want to try turnign your brightness up and see if u see anything on your tv.

 

btw: if i may ask, what did the guy hit u for the system?

[+Mitch]

Do you have any soldering experience? If you do, you can try replacing the three electrolytic capacitors as well as the voltage regulator.

 

Mitch

[Curt Vendel]

He may also want to adjust the pot settings first, a good couple of turns all the way in each direction then setting them back while its on could certainly help with the picture issue. If that doesn't work, he should try testing the output voltage on the p/s to make sure its not the cause, then yes replace the 7805, see if that corrects things, otherwise he may have to replace a few more things, I'd just it in a step by step approach to see if he can nail down the issue without desoldering first.

 

 

 

Curt

 

Do you have any soldering experience? If you do, you can try replacing the three electrolytic capacitors as well as the voltage regulator.

 

Mitch

[Rex Dart]

Well first off congrats on being a 7800 owner, with that being said, i am wondering of u cleaned the pins in the cart slot fist of all, and 2nd the audio might be a problem with a loose solder joint/joints.

 

as for the video u might want to try turnign your brightness up and see if u see anything on your tv.

 

btw: if i may ask, what did the guy hit u for the system?

 

Well, the thing is that 7800 games display with what I'd call perfect brightness... just as you would expect from a game system. So I'm thinking maybe it's something to do with the separate 2600 chips in the system? I've read a bit about how they're put together, but I don't know a whole lot just yet. I'm not afraid to take this sucker apart though, I'm pretty decent with a soldering iron. (I can even spell 'solder'!) And it cost me 66USD for the system, pair of paddles, a mushy proline, and a broken quickshot (that I'm going to use the cord from & make a new stick).

 

 

Do you have any soldering experience? If you do, you can try replacing the three electrolytic capacitors as well as the voltage regulator.

 

Sure do, so thanks for that suggestion. I'm going to take it apart right now, write down the specs on those parts, and head to the electronics store.

 

 

He may also want to adjust the pot settings first, a good couple of turns all the way in each direction then setting them back while its on could certainly help with the picture issue. If that doesn't work, he should try testing the output voltage on the p/s to make sure its not the cause, then yes replace the 7805, see if that corrects things, otherwise he may have to replace a few more things, I'd just it in a step by step approach to see if he can nail down the issue without desoldering first.

 

Cool, is that the one that's visible when you've taken the plastic apart but left the shielding on? If so, I'll give that a try too. I think the power supply is fine, but I'll test that too.

 

Thanks for all the tips, folks.

[Curt Vendel]

you can turn them with your fingers DON'T use a metal screw driver!

 

Well first off congrats on being a 7800 owner, with that being said, i am wondering of u cleaned the pins in the cart slot fist of all, and 2nd the audio might be a problem with a loose solder joint/joints.

 

as for the video u might want to try turnign your brightness up and see if u see anything on your tv.

 

btw: if i may ask, what did the guy hit u for the system?

 

Well, the thing is that 7800 games display with what I'd call perfect brightness... just as you would expect from a game system. So I'm thinking maybe it's something to do with the separate 2600 chips in the system? I've read a bit about how they're put together, but I don't know a whole lot just yet. I'm not afraid to take this sucker apart though, I'm pretty decent with a soldering iron. (I can even spell 'solder'!) And it cost me 66USD for the system, pair of paddles, a mushy proline, and a broken quickshot (that I'm going to use the cord from & make a new stick).

 

 

Do you have any soldering experience? If you do, you can try replacing the three electrolytic capacitors as well as the voltage regulator.

 

Sure do, so thanks for that suggestion. I'm going to take it apart right now, write down the specs on those parts, and head to the electronics store.

 

 

He may also want to adjust the pot settings first, a good couple of turns all the way in each direction then setting them back while its on could certainly help with the picture issue. If that doesn't work, he should try testing the output voltage on the p/s to make sure its not the cause, then yes replace the 7805, see if that corrects things, otherwise he may have to replace a few more things, I'd just it in a step by step approach to see if he can nail down the issue without desoldering first.

 

Cool, is that the one that's visible when you've taken the plastic apart but left the shielding on? If so, I'll give that a try too. I think the power supply is fine, but I'll test that too.

 

Thanks for all the tips, folks.

[Gorf]

IF you go to Radio Shack, you can get a plastic pot tool to turn those with. But as Curt said do not use a metal

tool as this can mess with the value of the pot/coil/whathaveyou.

[Rex Dart]

Update!

 

I wasn't able to find ANY replacement parts at the local store. They had NO 16v capacitors, and were sold out of 7805's. So I just took my soldering iron to the system and re-flowed all the solder joints on those components, plus anything that looked a little fishy. Sounds works now! Video's better, but mainly because I cranked up the TV's brightness. That seems to be all that I lacked in the video department, though Defender 2 is still insanely dark (ideas?), so I'm still thinking about adding composite video output to this thing.

[gdement]

Is it just Defender 2 that has a problem?

If there's still a general 2600 brightness issue, I'd use the 7800 board schematic and look for components that might only affect 2600 mode and not 7800.

The schematic is here:

http://www.atariage.com/7800/archives/index.html?SystemID=7800

 

 

Look on the right side of the schematic. Brightness in 2600 mode originates in the TIA chip (U8) from pins 8,5,7 which are marked LUM0, LUM1, LUM2. These are a binary +5v/GND signal, giving 8 levels of brightness. They get mixed with 7800 signals at U3 (bottom right corner of schematic), but prior to that point they're separate.

I suppose there could be a bad resistor at R19, R20, R21 or R23 that would cause 2600 mode to be dark. Maybe some other parts could also be involved.

I don't know where those resistors are on the board, but some continuity testing should find them.

[Rex Dart]

Is it just Defender 2 that has a problem?

 

I really don't know. I don't have enough experience with these systems to tell you for sure. If I can get some photos of a couple games, could you tell me if it's something I need to worry about?

 

 

If there's still a general 2600 brightness issue, I'd use the 7800 board schematic and look for components that might only affect 2600 mode and not 7800.

The schematic is here:

http://www.atariage.com/7800/archives/index.html?SystemID=7800

Look on the right side of the schematic. Brightness in 2600 mode originates in the TIA chip (U8) from pins 8,5,7 which are marked LUM0, LUM1, LUM2. These are a binary +5v/GND signal, giving 8 levels of brightness. They get mixed with 7800 signals at U3 (bottom right corner of schematic), but prior to that point they're separate.

I suppose there could be a bad resistor at R19, R20, R21 or R23 that would cause 2600 mode to be dark. Maybe some other parts could also be involved.

I don't know where those resistors are on the board, but some continuity testing should find them.

 

Thanks for the diagrams. I'll see what I can manage, but this sounds like a lot of work after all. Guess I should have expected this, buying from ebay and whatnot.

[gdement]

Is it just Defender 2 that has a problem?

 

I really don't know. I don't have enough experience with these systems to tell you for sure. If I can get some photos of a couple games, could you tell me if it's something I need to worry about?

I don't play much 2600, and I've never seen the 2600 Defenders at all, so I'm probably not the best person to tell you what they should look like. But there's plenty of people who could probably help.

[jmetal88]

Dang dude, I feel sorry for people when I read things like this.

 

I won an auction for an 'untested' 7800 and 2600 one time at around $30 (shipped), without power supplies or controllers or anything. I cobbled together a power supply for the 7800 and it worked fine after I adjusted the colors. The 2600 ended up not working. Well, either that or it was actually a PAL console, as the video output looked out of sync and scrambled on my TV.

 

All I wanted was the 7800 though, and I was pleased to have gotten it so inexpensively.