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7800 not booting, weird display / sound


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#1 Nmitchn47 OFFLINE  

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Posted Sun Dec 3, 2017 4:00 PM

Hi guys, I've got a later model 7800 that is not booting up with either a 7800/2600 game or with no game. No logo appears at all for any function. It's a CA025233-002 Rev B board. It would never work since I bought it used so I figured the RF was to blame. I changed it out to the AV mod with the Pokey wire added and still nothing. I measured a 5.13 volts from the voltage regulator so I replaced it and now have a 4.98 volts throughout the board. Incoming is at 10v, regulator outputs and all the way to the AV mod is measuring at 4.98v. I ended up replacing the 220uf capacitors (main / minis) with new and also replaced the MJE210 with a brand new unit. Power switch is good and no broken connections on the board visible, both sides.

Attached are two videos showing how it acts. Every time you start it, different forms of static to lines to colored lines appear. A 7800 / 2600 game does not change the output, nor does no game at all.

What direction of diagnostics could I try? Could it be a bad chip or connection? The unit is in good shape so it makes me wonder if it ever worked when it was bought new.





#2 DanthWader OFFLINE  

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Posted Sun Dec 3, 2017 4:14 PM

Any way we could have a close up photo of the A/V mod and all wires connected to the board. I may be of no help but i'm sure that may shed some light on someone more savvy.



#3 Nmitchn47 OFFLINE  

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Posted Sun Dec 3, 2017 4:23 PM

I don't have a good close up picture but it was replicated exactly from the retrofixes.com writeup and checked over for correct transitor paths and solder points. Its actually acting the same as it did when the RF modulator was installed.

Attached Thumbnails

  • IMG_4284.JPG
  • IMG_4304.JPG

Edited by Nmitchn47, Sun Dec 3, 2017 4:25 PM.


#4 -^CrožBow^- OFFLINE  

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Posted Mon Dec 4, 2017 8:12 AM

Um...in your video you don't have a cart plugged into the console at least not in the first video. You will get those lines if you power it up without a cart inserted.



#5 Nmitchn47 OFFLINE  

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Posted Mon Dec 4, 2017 9:06 AM

Just proving that it does the same regardless with either a cart inserted or not. Now, correct me if I'm wrong but doesn't the 7800 have a logo display show up first, even if you don't have a game inserted? I was reading there are three modes the system runs in: internal maria, external maria and Tia?



#6 DrSidneyZweibel OFFLINE  

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Posted Mon Dec 4, 2017 9:18 AM

Just proving that it does the same regardless with either a cart inserted or not. Now, correct me if I'm wrong but doesn't the 7800 have a logo display show up first, even if you don't have a game inserted? I was reading there are three modes the system runs in: internal maria, external maria and Tia?

You're wrong, at least partly.

 

If the 7800 is an NTSC  USA/Canada model, it will not display anything if no cart is inserted.

 

If the 7800 is a PAL 7800 from Europe, but doesn't have Asteroids built into the BIOS - same thing, no cart, no display.

 

If the 7800 is a later model PAL 7800 with asteroids built in, then it would display the BIOS screen, then Asteroids. But really - that's no different than having the Cart in the slot.

 

Since you're in the US, and this appears to be an NTSC 7800 - it will never display anything unless you have a cart in the slot.



#7 Nmitchn47 OFFLINE  

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Posted Mon Dec 4, 2017 9:37 AM

Ok, sounds like I may have read a PAL setup with a booting screen somewhere and got it confused with the NTSC model I have.

 

Could this be a RIOT issue?



#8 Osgeld OFFLINE  

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Posted Mon Dec 4, 2017 9:40 AM

I'm fighting a similar issue I am narrowing it down, but in my case it was the power on reset circuit which contains the 74ls174,74ls32, and 4013 chips

I swapped out the 4013 and caps now mi e will sometimes boot if I rapidly cycle power. On my scope I can see the reset line is still junky so I ordered the other two chips since I did not have them on hand

 

also check the voltage across CR5, its an independent 5 volt reference for the reset circuit 


Edited by Osgeld, Mon Dec 4, 2017 9:45 AM.


#9 DrVenkman OFFLINE  

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Posted Mon Dec 4, 2017 9:42 AM

Until you show us how it acts with a working cart installed, it's very difficult to diagnose anything. 

 

Even so, it could be any number of things from a bad 6502 to bad MARIA to bad SRAM. Might also be bad logic chips in the reset circuit, as the prior poster indicates. But really, without a scope or logic probe and the knowledge of how to use them, and with a non-socketed board, it's really difficult to diagnose issue like this.



#10 -^CrožBow^- OFFLINE  

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Posted Mon Dec 4, 2017 9:54 AM

Actually I don't think the PAL consoles ever get the 7800 rainbow startup screen. That only comes up on the NTSC units because that is when the console is checking the encryption if I remember correctly? So I believe the PAL units with Asteroids built in just pop up asteroids as soon as they are powered on.

 

I had this similar issue a few years back. Couldn't get anything to come to life on a 7800. I used the shotgun approach but found it be both a bad MJE201 transistor and a small axial cap that was obviously blown apart. Can't remember if I changed out the 4013 on it..but maybe I did that as well. Once I did that and fully replaced the power switch, that 7800 was powering on like a champ! 

 

Also the parts I had on hand, all came from a loaner 5200 that was dead in many other ways so I'd like to think that 7800 is still all Atari made. Wonder who ended up with that 7800 now that I think about it?



#11 Nmitchn47 OFFLINE  

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Posted Mon Dec 4, 2017 12:27 PM

I had this similar issue a few years back. Couldn't get anything to come to life on a 7800. I used the shotgun approach but found it be both a bad MJE201 transistor and a small axial cap that was obviously blown apart. Can't remember if I changed out the 4013 on it..but maybe I did that as well. Once I did that and fully replaced the power switch, that 7800 was powering on like a champ! 

 

Do you know which MJE201 you replaced?



#12 Osgeld OFFLINE  

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Posted Mon Dec 4, 2017 1:04 PM

there's only one on the system, its between the power jack and the heat sink



#13 Nmitchn47 OFFLINE  

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Posted Mon Dec 4, 2017 1:20 PM

there's only one on the system, its between the power jack and the heat sink

 

Ok good, I didn't see any others unless I was missing an additional one hidden. Thanks!


Edited by Nmitchn47, Mon Dec 4, 2017 1:20 PM.


#14 Nmitchn47 OFFLINE  

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Posted Mon Dec 4, 2017 6:04 PM

also check the voltage across CR5, its an independent 5 volt reference for the reset circuit 


Just checked several working 2600 games on my 2600 and they will not work on the 7800. I checked the voltage at the CR5 and it's giving me 1.3v on one end, the other shorts the system out.

Edited by Nmitchn47, Mon Dec 4, 2017 6:05 PM.


#15 Nmitchn47 OFFLINE  

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Posted Mon Dec 4, 2017 6:27 PM

Well I take the back, after trying several games, Solaris magically worked for about 30 seconds. It took a second to load up and then it started to play. Once I was playing, it worked good and then the picture got scrambled and cut off. I got it back up and working again and wiggled the cartridge around and nothing happens, so no loose connection with the pins.

#16 Osgeld OFFLINE  

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Posted Mon Dec 4, 2017 6:47 PM

Just checked several working 2600 games on my 2600 and they will not work on the 7800. I checked the voltage at the CR5 and it's giving me 1.3v on one end, the other shorts the system out.

 

no I meant  the black lead of your meter on the bottom, and the read on the top (which has the black stripe) hence across ;)

 

well it booted once lol, if I were a betting man the reset circuit, which even with a scope is a bit of a pain in the ass to debug, or the clock circuit 


Edited by Osgeld, Mon Dec 4, 2017 6:49 PM.


#17 Nmitchn47 OFFLINE  

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Posted Mon Dec 4, 2017 6:54 PM

2.1 volts constant it's measuring. Originally I was checking it by grounding and probing with the positive.

Got Pac man to load and play but is finicky. Rechecked on my 2600 and it works like a charm. The graphics will jitter like a glitch. Solaris is working good but I'm unable to get other 2600 games to load. Still not a single 7800 game will load.

Edited by Nmitchn47, Mon Dec 4, 2017 6:56 PM.


#18 SignGuy81 OFFLINE  

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Posted Mon Dec 4, 2017 7:01 PM

Do you have another zener to try in place of CR5?  I've heard these can go intermittent but I've never came across one like that I've always usually had them short when bad and stay shorted.



#19 SignGuy81 OFFLINE  

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Posted Mon Dec 4, 2017 7:31 PM

My other guess would be bad 4013 chip I believe already mentioned.  Possibly pulling down the voltage.  I figured zener would be easiest to try if the chip isn't socketed.  Also what I would do if I didn't have a zener or a way to desolder the 4013, from going by the schematic I would lift the leg of R53 that is electrically connected to the zener, and also lift that leg of the zener that was electrically connected to the resistor.  Then I would get my bench supply, ground the grounds together and connect the 5V to where you lifted the leg of the zener.  Make sure current is set low and gradually increase.  That should put 5V where it needs to be and you can check to see if it works then or not repeatedly without any problems(if so replace the zener), or if is drawing too much current and if so I would would then suspect U10, the 4013 flipflop chip.


Edited by SignGuy81, Mon Dec 4, 2017 7:33 PM.


#20 Nmitchn47 OFFLINE  

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Posted Mon Dec 4, 2017 7:32 PM

Reading 2.1 volts at the zener and pin 14 of 4013. I'm assuming this is too low and needs to be 5v. What type of zenner can I replace it with?

#21 SignGuy81 OFFLINE  

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Posted Mon Dec 4, 2017 7:35 PM

https://www.ebay.com...HQAAOSwmnFZ46eb

 

May not be the problem however but that would be easiest to try.



#22 Nmitchn47 OFFLINE  

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Posted Tue Dec 5, 2017 8:02 AM

https://www.ebay.com...HQAAOSwmnFZ46eb

 

May not be the problem however but that would be easiest to try.

 

Just ordered them, should be here by weeks end so I can update. Thanks for the link. If this doesn't work I'll order a socket and 4013 to test.

 

I'm assuming that with roughly half the voltage required going to the flip flop 4013, it's barely functioning, but allowing the TIA to work?



#23 -^CrožBow^- OFFLINE  

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Posted Tue Dec 5, 2017 8:33 AM

Okay so in looking at your pic of your mainboard I remembered what parts I changed out on mine a few years back that wouldn't power up. 

 

So in addition to the MJE201 I mentioned earlier, I also had to replace the 4013 and put it in a socket because the small axial cap attached off pin 14 from the 4013 was completely toasted black. So something happened and likely took out the 4013 in mine. The cap sits just north of the 4013 between what looks like two 100ohm resistors there.

 

But it was those three parts I remember specifically changing out on mine. Hopefully that helps...



#24 Nmitchn47 OFFLINE  

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Posted Thu Dec 7, 2017 2:56 PM

Zener came in the mail and installed, reading 5v and 5v at pin 14 on the 4103 now. No improvement still. Atari will still boot up Solaris/Pac Man randomly, but will not run any 7800 cartridges. I left Solaris running and picture will randomly glitch or get garbled and then return to normal every through seconds, sometimes it will run fine. I did notice the 6502 chip is running rather warm compared to the rest, don't know if that's normal.

 

Side note, ran my voltmeter over the power supply end and it's measuring 11v. The regulator is measuring 11v input and 5v output to the board, this seems just way too high from the power supply. Is this ok?



#25 -^CrožBow^- OFFLINE  

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Posted Thu Dec 7, 2017 3:57 PM

Yes...11v is normal from the power supply. The power supply isn't regulated so they tend to run high. Hell, the powersupplies to my Sega Genesis combos all measure out about 13v to the regulators! The 7805 can take the voltage up to at least 12v I would imagine. It will just cause it to run hotter to expel that excess voltage.

 

So, you are able to run 2600 games, but no 7800 games correct? 






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