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Nmitchn47

7800 not booting, weird display / sound

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The title is "7800 not booting, weird display / sound" yet I see know mention of the sound issue in the posts. Also the first post with the videos I'm not seeing the audio cable connected to the TV, just the video cable. Can you describe what it is doing with the sound, or give us a video as well with the audio connected.

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in theory a 7805 is good for 25 volts ... course cause of the heat dissipation you would have to draw very little current, or bolt it to an ingot

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Did you give the cartridge port a good cleaning?

 

Yes, one of the first things I tried. Used both a cartridge to clean and a credit card with a cleaning swab soaked in rubbing alcohol. Slot was not dirty at all. All pins look to be in place and not bent.

 

The title is "7800 not booting, weird display / sound" yet I see know mention of the sound issue in the posts. Also the first post with the videos I'm not seeing the audio cable connected to the TV, just the video cable. Can you describe what it is doing with the sound, or give us a video as well with the audio connected.

 

This was before I knew the NTSC versions didn't have a boot screen. And yes, the first two videos didn't have the audio cable attached as I was more worried with the game loading. Audio from both jacks of the AV mod are good.

 

in theory a 7805 is good for 25 volts ... course cause of the heat dissipation you would have to draw very little current, or bolt it to an ingot

 

Good to hear. That would be bad since I replaced all the larger electrolytic capacitors.

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Here are two vidoes that I uploaded this morning of the 7800 running a 2600 game and what is doing with a 7800 game. I got Venture to work this morning surprisingly. So it seems (3) 2600 games are working with a few presses of the power button. Take note of the different sounds and screens that are shown with the 7800 Dark Chamber game inserted. Each time I press the power button is something different.

 

https://youtu.be/v0mZLunxCH0

 

https://youtu.be/Zb92OU8_hoM

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in theory a 7805 is good for 25 volts ... course cause of the heat dissipation you would have to draw very little current, or bolt it to an ingot

 

Have you seen the heatsink on a 7800? :P

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Have you seen the heatsink on a 7800? :P

 

Before I cracked open the system, I had never seen one so large for a 9v setup. :o

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I'm following the 7800 repair flowchart and it says to check a low depression on some of the pins. How would one go about doing so?

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Before I cracked open the system, I had never seen one so large for a 9v setup. :o

And yet the 7805 in the 7800 is prone to failure more often than the 2600s 7805 regulators....go figure.

 

I think the largest heatsink assembly for a 7805 would go to the either the 5200 as it has two of them each with their own large heatsink, or possible the heatsink used on the Genesis model 1, although those heatsinks have two 7805s attached.

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I'm following the 7800 repair flowchart and it says to check a low depression on some of the pins. How would one go about doing so?

 

Can you take a pic zoomed in on the cartridge port so we can see the pins.

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if you flip the board over there's a couple screws holding the cart guide, take those out and it should come free, then you have a clear view of the connector

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could be, in the video the LED fires right up though (which is on the 5 volt side of the power on circuit)

Edited by Osgeld

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I’m having a similar issue with my 7800. I was playing it just fine, and switched games and never could get it running again. Anyone have a link listing troubleshooting steps? Thanks

 

 

Sent from my iPhone using Tapatalk

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just an update on mine, got parts in sometime last week, dropped in a new 74LS32 and a 74LS174, and had already replaced the 4013 and now it boots all the time every time

 

I got a couple of each so if the OP wants to pay for postage and is willing to solder some chips I don't really need the extra's now

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Would a flaky power switch cause these issues? Seems to take a few presses to get a game going.

 

Tested it after the regulator didn't work, working good.

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just an update on mine, got parts in sometime last week, dropped in a new 74LS32 and a 74LS174, and had already replaced the 4013 and now it boots all the time every time

 

I got a couple of each so if the OP wants to pay for postage and is willing to solder some chips I don't really need the extra's now

 

Osgeld, I would be hugely interested in whatever leftovers you might have. PM me and I'll forward payment via Paypal. :)

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Looking at the first pic, have you verified that those nicked traces about a centimeter from the lower right of the cart port are good? hard to tell in the pic if they are fully intact or not and I believe those traces comes from the rightmost pins off the cart port. Those pins would only be used by 7800 games.

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Looking at the first pic, have you verified that those nicked traces about a centimeter from the lower right of the cart port are good? hard to tell in the pic if they are fully intact or not and I believe those traces comes from the rightmost pins off the cart port. Those pins would only be used by 7800 games.

 

After looking back on the picture again, you might be on to something. I'll check them out later today.

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And yet the 7805 in the 7800 is prone to failure more often than the 2600s 7805 regulators....go figure.

 

I think the largest heatsink assembly for a 7805 would go to the either the 5200 as it has two of them each with their own large heatsink, or possible the heatsink used on the Genesis model 1, although those heatsinks have two 7805s attached.

 

The heatsink on the 1200XL is pretty ginormous - also two 7805's, but in that machine, the heatsink also helps the 12V rectifier; what a silly power system design that system has: 9VAC from the wall, rectified to 12VDC, then stepped down by two 7805s to 5VDC. What kind of grass were those guys on? And why they didn't just spec a 9VDC power supply I'll never know.

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Surprised I didn't see this before but everything checked good with a continuity test on both ends of the traces for all three. Also no shorting between traces. Double checked continuity at the slot pins and motherboard while I was it. The cartridge guide had a sharp edge on the bottom plastic where it was pressing down on the motherboard and digging into the traces. Poor molding of the piece back in the day. Someone before me may have bashed the game in the slot figuring it would help fix it.

post-62762-0-48685000-1513038943_thumb.jpg

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How manay different games have you tried?

All games clean?

The 7800 hates being dirty.

 

Crossbow, Dark Chambers, Pole Position 2, Ms Pac Man and Centipede

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