Author Topic: SNES black screen at startup  (Read 17491 times)

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Offline poot36

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SNES black screen at startup
« on: June 01, 2015, 12:28:33 am »
I have a SNES that gives me a black screen at startup.  I have tried cleaning the cartridge connector and it has not made any difference.  I have noticed that if I tilt the cartridge (on the left hand side with the front of the console facing you) it will sometimes display colored blocks on the screen or play a sound effect from the game (not correlated to what should play on startup).  The game that did this was Super Mario World, all of my other games did not do anything besides the black screen.  I have went as far as to create my own connector from two floppy drive connectors for the 5 1/2" drives and it just made the game stay on a black screen.  I think that it did this because all of the data and address lines were properly connected and that activated the fault.  I have tested for continuity between all of the cartridge pins and the SNES and have found no problems.  Is there some small rom that I could connect to my custom cable that uses the minimum amount of the address lines and activates the minimum parts of the SNES for either video display or sound?  I have disabled the CIC chip by lifting pin 4 and have confirmed with a scope that the console is not reseting even without a game in it.  Will I need a logic analyzer to find this fault?  Or will my Tektronix 465 scope be enough along with my multimeter?
« Last Edit: July 29, 2015, 05:14:54 am by poot36 »
 

Offline McBryce

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Re: SNES black screen at startup
« Reply #1 on: June 01, 2015, 09:55:53 am »
Have you checked the solder joints under the cartridge connector? Also check that the reset button isn't jammed. I doubt you'll need an LA to fix this. If just one data/address bit was missing you'd at least get a screen full of garbage.

McBryce.
 

Offline poot36

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Re: SNES black screen at startup
« Reply #2 on: June 02, 2015, 03:50:57 am »
Ok, I have checked and rechecked all of the solder joints with a multimeter set on diode mode and they all show the chips internal output or input diode.  The only interesting ones were the data lines which had a 0.3V diode versus the address lines that had a 0.5V diode.  Some of the remaining lines had a 0.6V diode.  Also checked the connection to the rom chip in the cartridge and it is fine to.  I have also checked the reset button and it goes low when pressed and returns to high when released.  I have a Sony PVM1944Q broadcast monitor that shows what video mode you are in and it is detecting a NTSC signal from the SNES when I have a game in the console (even with the black screen).  I have disabled the lockout chip to eliminate that as a problem.  I do have the front panel joystick board disconnected, could that cause problems?
 

Offline McBryce

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Re: SNES black screen at startup
« Reply #3 on: June 02, 2015, 09:15:44 am »
I do have the front panel joystick board disconnected, could that cause problems?

It shouldn't.

McBryce.
 

Offline poot36

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Re: SNES black screen at startup
« Reply #4 on: June 03, 2015, 05:18:46 am »
Ok, I suspected that the front panel would not make any difference.  What should I try to test next?  I can see the cpu looping through what I assume are addresses with the scope when there is no cart in the console.  With a cart the data and addresse lines sometimes stay static at a high or low after power on or a reset and sometimes stay looping instead.  Would knowing what the hex value of the data and addresse lines are in these two states help me debug the console?  Could I use my Arduino to convert the 8 bit data bus into hex and send it to the computer through the serial port or would storing on the Arduino and then sending it to the computer be a better idea?
 

Offline tyguy2

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Re: SNES black screen at startup
« Reply #5 on: June 08, 2015, 12:27:14 am »
You might want to check the reset line going to the SNES. Sometimes the PCB gets scuffed and scratched, causing it to just have a black screen. Alternatively, try holding down reset for 10 seconds and releasing.

Read this:
http://techforums.nintendo.com/thread/5834
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Offline poot36

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Re: SNES black screen at startup
« Reply #6 on: June 08, 2015, 03:05:53 am »
I have tried cleaning the cart slot multiple times as well as making my own cart slot and it still does not work.  I have checked the 3 individual reset lines and they appear to be working but /resout1 does have some noise on it (0.1V to 0.2V).  With my crappy Arduino based logic analyzer I have found that the data bus likes to stop at random hex codes but does not continue to run.  When I start the console with the power switch I have never had the data or address lines do anything until I toggle the reset button a few times.  Also on the first power up with just having plugged in the power supply and turned on the power switch I will consistently get a blue diamond hatch screen that fades to a green diamond hatch screen and then that fades to black or sometimes just the green diamond hatch screen and a fade to black.  I have even tried re soldering all of the chips and components from the front of the console to the cart connector and that did not make any difference.  I have noticed that the /pard and /pawr lines stay high all of the time as well and I have never got any data on the video ram.  Does anyone in Calgary have a broken or working older logic analyzer that they do not want?  I think it will help me properly find the fault instead of shooting in the dark.
 

Offline tyguy2

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Re: SNES black screen at startup
« Reply #7 on: June 08, 2015, 03:14:22 am »
This may seem obvious, but have you tried replacing the caps? :-//
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Offline poot36

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Re: SNES black screen at startup
« Reply #8 on: June 08, 2015, 03:47:01 am »
I have not tried replacing the caps yet but I have measured the ripple on the power supply rail and it is at most 200mV peak to peak.  None of the caps appear to be leaking or bulging  but I guess I could try it.
 

Offline Spyke

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Re: SNES black screen at startup
« Reply #9 on: June 11, 2015, 09:22:05 pm »
This is where a good bench supply comes in handy, supplying a clean 5V after the 7805 regulator could rule this out quick.

EDIT: People are using phone chargers to power the SNES as its more efficient, try that. Would allow you to remove the dodgy supply cap, just bypass the 5V with a small cap at the SNES if not already.
« Last Edit: June 11, 2015, 09:25:19 pm by Spyke »
 

Offline tyguy2

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Re: SNES black screen at startup
« Reply #10 on: June 11, 2015, 09:24:27 pm »
If you have an old ATX power supply, that should do in a pinch.
http://www.instructables.com/id/ATX--%3E-Lab-Bench-Power-Supply-Conversion/step2/Planning/

However, if you don't have a 10 ohm 10 watt resistor, a couple of LED's will work.
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Offline Johndi

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Re: SNES black screen at startup
« Reply #11 on: June 12, 2015, 09:56:05 am »
If there is a Radio Shack still open near you that is closing, generic USB chargers are around $5 or so right now.  Good cheap option for a 5V supply.
 

Offline tyguy2

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Re: SNES black screen at startup
« Reply #12 on: June 12, 2015, 12:33:27 pm »
There is no way a USB port could provide enough amprage to a SNES.
Never mind, I thought you meant coming from a computer. :-DD
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Offline poot36

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Re: SNES black screen at startup
« Reply #13 on: June 13, 2015, 08:25:53 pm »
Ok, I have tried a 5V 2A USB charger and a old AT power supply (properly loaded) and it still does the same thing.  I have found that by pressing and releasing the reset switch with varying speeds will sometimes cause a display of garbled blocks that appear to change as time goes on (I think this is the intro playing of the game but I am not sure).  It will also do this with the prober SNES power adapter as well.  I have tested the sound card in another SNES and that works fine.  What would the best tool be to look at the three reset lines in the time domain?  I am thinking of getting a logic analyzer but I am not sure if this is the right tool for the job.
 

Offline SaabFAN

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Re: SNES black screen at startup
« Reply #14 on: June 14, 2015, 12:35:40 pm »
Have you checked the copy-protection/region-lockout-chip?
If it doesn't get the right keys or is damaged, it might cause the system to lock up. On the NES, the region-lockout Chip continually send a reset-signal to the Main CPU when the cart didn't send the correct response.

Offline tyguy2

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Re: SNES black screen at startup
« Reply #15 on: June 14, 2015, 02:39:57 pm »
 |O I can't believe we didn't think of that before! That's probably it.
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Offline poot36

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Re: SNES black screen at startup
« Reply #16 on: June 14, 2015, 03:24:04 pm »
I have actually disabled the lockout chip by lifting pin 4.  That way it acts like a key not a lock.  The SNES still acts the same way though.  Should I try removing the power or ground pins to totally disable the chip?  I do believe that the fuzzy looking reset trace is coming from this chip but I am not 100% sure.  I guess that I could disconnect the reset out pin of this chip and look at the quality of its signal.
 

Offline tyguy2

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Re: SNES black screen at startup
« Reply #17 on: June 14, 2015, 03:38:21 pm »
Ah! Try providing 5v or ground to pin 4!  :scared:
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Offline poot36

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Re: SNES black screen at startup
« Reply #18 on: June 14, 2015, 03:44:09 pm »
I think that I have tried grounding pin 4 but I have not tried powering it.  Will give that a go and get back to you.  Although I have seen many tutorials that just say to lift the pin and that you only need to power or ground it if you are trying to play a few types of games that check for correct lockout chip operation.
 

Offline tyguy2

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Re: SNES black screen at startup
« Reply #19 on: June 14, 2015, 04:01:06 pm »
Make sure pin 4 is either grounded OR put at 5v before you turn the console on. :-+
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Offline poot36

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Re: SNES black screen at startup
« Reply #20 on: June 15, 2015, 04:25:59 am »
Ok, with pin 4 grounded I have a fairly high chance of getting blue flashing bars on the screen when using the power switch.  When the pin is grounded it turns the lockout chip into a key chip thus disabling it.  If I press the reset button the blue bars will go away to be replaced by the black screen.  I have sometimes managed to get white flashing bars or other colored blocks appearing on the screen as well.  I think I will attach a wire to the pin and ground it with a way shorter lead then my 1.5 foot alligator clip lead.  Then I will know the console will always start up in theory.
 

Offline tyguy2

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Re: SNES black screen at startup
« Reply #21 on: June 15, 2015, 04:38:05 am »
Is the SNES attached to a Cathode ray tube TV or an flat screen? If it is connected to a flat screen, try connecting to a CRT.
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Offline poot36

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Re: SNES black screen at startup
« Reply #22 on: June 15, 2015, 05:03:32 am »
It is attached to a Sony PVM series 19" broadcast studio monitor from 1992 with S-Video.  It is a great CRT monitor with RGB inputs that are switchable to Component inputs.  I have tested this setup with another SNES as well as a N64 and a Gamecube and it works quite well with razor sharp pixels.
 

Offline tyguy2

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Re: SNES black screen at startup
« Reply #23 on: June 15, 2015, 05:27:46 am »
Ok just checking. :-+
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Offline necroscope

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Re: SNES black screen at startup
« Reply #24 on: June 15, 2015, 09:43:18 pm »
Ok, with pin 4 grounded I have a fairly high chance of getting blue flashing bars on the screen when using the power switch.  When the pin is grounded it turns the lockout chip into a key chip thus disabling it.  If I press the reset button the blue bars will go away to be replaced by the black screen.  I have sometimes managed to get white flashing bars or other colored blocks appearing on the screen as well.  I think I will attach a wire to the pin and ground it with a way shorter lead then my 1.5 foot alligator clip lead.  Then I will know the console will always start up in theory.
I have seen these same symptoms trying to boot a dud cartridge before, have you tested more than one cartridge?
 


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