SNES black screen at startup - Page 1
Forum section: electronics / repair

author: poot36
author_rank: Frequent Contributor
timestamp: June 01, 2015, 12:28:33 am
content: 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?

author: McBryce
author_rank: Super Contributor
timestamp: June 01, 2015, 09:55:53 am
content: 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.

author: poot36
author_rank: Frequent Contributor
timestamp: June 02, 2015, 03:50:57 am
content: 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?

author: McBryce
author_rank: Super Contributor
timestamp: June 02, 2015, 09:15:44 am
content: Quote from: poot36 on June 02, 2015, 03:50:57 amIt shouldn't.McBryce.

author: poot36
author_rank: Frequent Contributor
timestamp: June 03, 2015, 05:18:46 am
content: 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?

author: tyguy2
author_rank: Unknown
timestamp: June 08, 2015, 12:27:14 am
content: 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

author: poot36
author_rank: Frequent Contributor
timestamp: June 08, 2015, 03:05:53 am
content: 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.

author: tyguy2
author_rank: Unknown
timestamp: June 08, 2015, 03:14:22 am
content: This may seem obvious, but have you tried replacing the caps?

author: poot36
author_rank: Frequent Contributor
timestamp: June 08, 2015, 03:47:01 am
content: 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.

author: Spyke
author_rank: Contributor
timestamp: June 11, 2015, 09:22:05 pm
content: 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.

author: tyguy2
author_rank: Unknown
timestamp: June 11, 2015, 09:24:27 pm
content: 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.

author: Johndi
author_rank: Contributor
timestamp: June 12, 2015, 09:56:05 am
content: 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.

author: tyguy2
author_rank: Unknown
timestamp: June 12, 2015, 12:33:27 pm
content: There is no way a USB port could provide enough amprage to a SNES.Never mind, I thought you meant coming from a computer.

author: poot36
author_rank: Frequent Contributor
timestamp: June 13, 2015, 08:25:53 pm
content: 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.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 14, 2015, 12:35:40 pm
content: 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.

author: tyguy2
author_rank: Unknown
timestamp: June 14, 2015, 02:39:57 pm
content: I can't believe we didn't think of that before! That's probably it.

author: poot36
author_rank: Frequent Contributor
timestamp: June 14, 2015, 03:24:04 pm
content: 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.

author: tyguy2
author_rank: Unknown
timestamp: June 14, 2015, 03:38:21 pm
content: Ah! Try providing 5v or ground to pin 4!

author: poot36
author_rank: Frequent Contributor
timestamp: June 14, 2015, 03:44:09 pm
content: 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.

author: tyguy2
author_rank: Unknown
timestamp: June 14, 2015, 04:01:06 pm
content: Make sure pin 4 is either grounded OR put at 5v before you turn the console on.

author: poot36
author_rank: Frequent Contributor
timestamp: June 15, 2015, 04:25:59 am
content: 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.

author: tyguy2
author_rank: Unknown
timestamp: June 15, 2015, 04:38:05 am
content: 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.

author: poot36
author_rank: Frequent Contributor
timestamp: June 15, 2015, 05:03:32 am
content: 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.

author: tyguy2
author_rank: Unknown
timestamp: June 15, 2015, 05:27:46 am
content: Ok just checking.

author: necroscope
author_rank: Regular Contributor
timestamp: June 15, 2015, 09:43:18 pm
content: Quote from: poot36 on June 15, 2015, 04:25:59 amI have seen these same symptoms trying to boot a dud cartridge before, have you tested more than one cartridge?

author: tyguy2
author_rank: Unknown
timestamp: June 15, 2015, 10:17:57 pm
content: What game are you using? Does it use Mode 7 or the Super FX chip?

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 15, 2015, 10:51:29 pm
content: Maybe this will help: Full Schematicshttp://forums.nesdev.com/viewtopic.php?f=12&t=10470I think, the next thing to do would be to get a logic analyzer and check what is really happening on the Address- and Data-Lines. At 3,58Mhz, the SNES runs slow enough for a Arduino-Zero based logic-Analyzer. Maybe even slow enough for a normal Arduino. There are ready to use Arduino-Sketches and Readout-Software on the Net available.Also check all the lines on the CPU for the LOW and HIGH-Levels. If there is something wrong with the Cart-Connector, or the decoupling-caps of the Carts themselves, this is where it should show. The Data-Lines are probably the most likely suspect.

author: poot36
author_rank: Frequent Contributor
timestamp: June 16, 2015, 05:15:32 am
content: I have made a short (under 1 inch) jumper from pin 4 to pin 9 (ground) and can confirm that the SNES stays running. It however has not solved the problem. Sometimes on power up using the power switch it still does not start trying to read the cart. I do have the schematic for the second version of the SNES (1993 and onwards) but not for my first version SNES (1990 to 1992). Mine is from 1990. I am using Super Mario World as a test cart as this is the only one that I have had any luck getting anything to display on screen or output sound. It does not have a super FX chip or other accelerator chip in it. Not even a memory maper chip. I have tried other games but I get even less of a result with them. I have tried turning my Arduino UNO into a logic analyzer but I am not sure that I am doing it right. I have one program that uses digital reads and stores them and then converts them into hex and outputs them from the serial port and another that reads directly from the port B and D registers and outputs that as a 0 to 255 number from the serial port. Tomorrow I will try to attach the two programs and then you people can tell me which would run faster. I may end up getting one of those cheap (~$10) USB 8 bit 24Msps logic analyzers off eBay but I am not sure what software to use with it. Would the SUMP software work or is there a better free and legal one out there that preferably can convert the 8 bit data to hex?

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 16, 2015, 09:05:46 am
content: With the cheap Thingies from ebay, you mostly use this software:https://www.saleae.com/logic/If you can get one for 10$, go for it. I have one of those things here and its really helpful, especially as with the PC you basically have virtually unlimited memory compared to a DS1054Z.The Scaleae-Software also has a lot of decoding-options. BUT The massive drawback: These USB-Thingies are only 8-Bit, whereas the SNES uses 32bit (16bit Address-Bus and 16bit Data-Bus). To really check what's going on in there, you need something more expensive and powerful.What I would do instead: Check if the Voltage-Levels for LOW and HIGH are within spec when a Cart is plugged in. That way you can quickly rule out any broken connection between the processor and the Memory inside the Cart.

author: poot36
author_rank: Frequent Contributor
timestamp: June 17, 2015, 03:51:17 am
content: Ok, I have downloaded the latest SNES schematics (V1.5 instead of my V1.1 version). I have attached my Arduino logic analyzer files to this post they are rar but relabeled as zip. I will double check the voltage levels as well. Also in reading the SNES schematics there is a 8 bit data bus a 16 bit A address bus as well as a 8 bit B address bus on the cartridge slot. I am going to be focusing on the data bus as well as the 16 bit A address bus for my meter measurements. I have also used continuity mode on my meter to double check all of the cart connections to the eprom chip inside and they were all good. I even made my own cart connector just to eliminate any connection problems and it did not change any of the results.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: June 17, 2015, 08:08:34 pm
content: What? Only 8 Bit Data-Bus? So the SNES isn't a true 16bit-System?No wonder (SEGA) Genesis did what Nintendon'tI think, after you've ruled out dodgy connections between CPU and Cart, the next step would be to work your way back from the Encoder-Chip to the PPUs and eventually the CPU itself.

author: McBryce
author_rank: Super Contributor
timestamp: June 17, 2015, 08:30:22 pm
content: The SNES has a CPU based on the 65C816, so it's a 16bit core, crippled by an 8 bit databus.Bryce.

author: tyguy2
author_rank: Unknown
timestamp: June 17, 2015, 08:37:05 pm
content: I think the 8 bit data bus was included to allow backwards compatibility with the NES, but it was never implemented.

author: poot36
author_rank: Frequent Contributor
timestamp: June 18, 2015, 04:33:52 am
content: Here is a scope picture of the D5 pin on the cartridge slot with out a cart in it.

author: poot36
author_rank: Frequent Contributor
timestamp: June 18, 2015, 04:35:12 am
content: Here is a scope picture of the A5 pin on the cartridge slot with out a cart in it.

author: poot36
author_rank: Frequent Contributor
timestamp: June 18, 2015, 04:36:50 am
content: And here is the test setup.

author: poot36
author_rank: Frequent Contributor
timestamp: June 18, 2015, 05:19:40 am
content: All of the scope shots were taken with the 20 Mhz bandwidth switch turned on, 2 Volts per division, DC coupling and DC trigger turned on, positive trigger, and I think the same timebase but I am not sure about that ( I know it was in the µs for sure) on a Tektronix 465. I don't know about you but the data bus seems very messed up! Unless my scope does not like properly triggering on certain digital waveforms I don't think there should be a flat portion at around 1 to 2 volts! Or is this caused by the pins trying to read data but picking up noise? I do know after turning on the console with the power switch it will usually not even start running through the address and data lines but will hold them high or low or in that 1 to 2 volt region and showing small square or sine wave action on the scope. If I monitor the pins with the scope and press and release the reset button I can sometimes get what you see in the pictures. If I am really lucky I will get random video output and then I do also see action on the data and address lines on the video ram chips. If there is no video output the data and address lines on the video ram chips usually stay high but sometimes will stay low or a combination of the two. I have also noticed that there is almost 0.5V of ripple on the reset line that goes to the CPU and a few other chips. Is this normal? This reading was taken on my non RMS multimeter set on AC mode.

author: Anks
author_rank: Frequent Contributor
timestamp: June 18, 2015, 07:10:01 am
content: Looks like you have some form of bus contention on the D5 line or whatever is driving it is failing.

author: McBryce
author_rank: Super Contributor
timestamp: June 18, 2015, 08:08:30 am
content: Yup, I'm with Anks. There's two sources writing data to the bus at (almost) the same time.Bryce.

author: poot36
author_rank: Frequent Contributor
timestamp: June 19, 2015, 04:15:13 am
content: I have found that I can not get consistent scope traces at power up with the power switch but if I press reset I usually will get a consistent trace but not all the time! I am now really thinking there is a reset problem but I can not track it down. I have tried finding the 0.4V of ripple on the reset line but I have tried lifting all of the chip pins that it goes to and it is still there. Can a bad resistor cause ripple? I know that R74 on the schematic shows 1K but mine is 2.2K. This resistor is between the U3 (S-PPU2) chip and all of the other chips that need reset. I have also figured out that the CPU is sending the reset signal not U3 (S-PPU2). I am not sure if this is normal or not. I have attached pictures of the same signals (D5, A5 and screen) under the same conditions (I have removed the Arduino on the data pins but this shoud not make much difference) but a different power on and reset procedure as well as what I managed to get on screen. There is no cart in the SNES.

author: tyguy2
author_rank: Unknown
timestamp: June 19, 2015, 12:21:33 pm
content: Quote from: poot36 on June 08, 2015, 03:05:53 amWhy don't you try bypassing the PCB all together and just put each reset to what you want them to be. Try soldering each reset pin high and low. Make sure there is a cart in the SNES, it only boots if a cart is inserted.

author: tyguy2
author_rank: Unknown
timestamp: June 20, 2015, 09:54:47 pm
content: Have you tried just using the A/V input? The S-Video may be messing up.

author: poot36
author_rank: Frequent Contributor
timestamp: June 21, 2015, 05:57:32 am
content: Well I think I am an idiot, the noise that I was seeing on the reset line was from the 24 Mhz clock line opposite to the reset lin in the cart connector. I think my extended cart lines are causing some interference. I have tried with the S-Video and Composite outputs and I have verifyed with a scope that I only get an image when there is a analog signal on the RGB pins. I have compared the noise on the reset line with a working SNES and there is actually more high frequency noise on the working SNES then the non working one so I think that rules that out. I still do not know why the SNES will usually not start with the power switch but requires using the reset switch to start activity on the address lines most of the time. I wonder if the method of disableing the lockout chip can cause startup problems. I am in the process of making a simple test cart that will just show a sold color on the screen and that is it. I think I have burned the eeprom with the *.smc file correctly ( I changed the *.smc extension to *.bin to get the programmer software to see it but I am not sure if this is the right way to do it) and am deciding whether to get a cheap cart and remove the original rom chip or wire up 2 connectors to plug into my floppy drive cable ports and attach them to a 32 pin socket for the eeprom. The first option would be faster but would also have more chips on the board to potentially cause more problems. The second option would take more time but should also work assuming that the schematics are correct (for some reason the address lines on the pinout for the cart rom chips do not match the cart connector pinouts at least on Super Mario World). Which one of these methods would you recommend? Quick question should the output of the crystal oscillators look like a sine wave on my scope? After one goes into a buffer chip it does look like a proper square wave on my scope. Also have just figured out that at least one of my scope probes is having a funny problem that causes the waveform to have curved edges on a square wave. On the output of the compinsation trimmer block that has the BNC connector on it if I wiggle the cable there the waveform will go funny. I have noticed that this section can be unscrewed and I have checked that it is tight. Is there something that I can do to fix the problem or do I need to buy a new scope probe cable or compinsation trimmer block? This is a Tektronix probe with the 10x id pin on the BNC connector.

author: justanothercanuck
author_rank: Frequent Contributor
timestamp: July 05, 2015, 02:43:29 am
content: Just throwing it out there... You might want to check out nesdev for this kind of stuff.That said, if you've checked the main input capacitor and you're still getting a black screen on startup, you might want to look at the (main PCB) SRAM chips, mainly the one for the CPU. If swapping the PPU and CPU SRAMs around doesn't change anything, then it might be the extended traces after all. Throwing some buffers into the mix might help a bit.edit: yes sorry, I was confusing the NES and the SNES (the NES RAM chips are identical, not the SNES). I would still try the input cap though.

author: poot36
author_rank: Frequent Contributor
timestamp: July 05, 2015, 02:59:12 am
content: I will have a look at that forum as well. The SRAM chips for the CPU and the PPU are not interchangeable. The SNES was having problems before I extended the cartridge lines. I don't think they could be causing problems though because I have seen in portable SNES mods cables around this length as well.

author: poot36
author_rank: Frequent Contributor
timestamp: July 13, 2015, 05:52:21 am
content: Well I have done more testing and can confirm that the power on reset chip appears to be working properly. The chip will cut out at 4.05V or so. However in the datasheet it is speced to cut out at 4.2V and the min level is 4.1V with a maximum of 100mV play in the voltage presumably to prevent it oscillating. I think that is in spec still (but may be on the low side). Can someone confirm that I am interpreting the data sheet correctly and if possible test what there SNES browns out at? ~4V seems rather low for 5V logic. The good news is that I should be getting my hp 1661C logic analyzer within 7 days or so. Then I can provide you guys with more useful data (I hope). Or I am going to be asking either how to properly use it or fix it.

author: tyguy2
author_rank: Unknown
timestamp: July 14, 2015, 05:54:39 pm
content: I just rembered this. Are you trying to use a PAL connection on an NTSC screen (or visa versa?). Some carts are not cross compatible, among other compatibility issues. Also, the SNES has a 50hz mode and a 60hz mode, so try looking into that. Have you checked the audio coming from the A/V port? If there is audio, then there may be hope. Also try connecting to a screen via the RF connector. Good luck

author: poot36
author_rank: Frequent Contributor
timestamp: July 15, 2015, 12:22:37 am
content: I have checked that I have a standard North American SNES and cartridges. The Sony broadcast monitor is capable of accepting all video formats and it does indicate that it is receiving a NTSC signal. I have only occasionally been able to get sound out but it is usually one effect and not related to the normal startup of the game. I am starting to suspect the PPU1 chip or the RAM chip for the CPU. Is it possible to run a SNES without the PPU1 and PPU2 chips active? I currently have the reset lines so that the two video chips should stay disabled but I am not sure if this is the right solution.

author: poot36
author_rank: Frequent Contributor
timestamp: July 29, 2015, 05:11:14 am
content: Update: I got a HP 1661C logic analyzer for less then $100 and have connected it to the SNES. I have found that even with the cartridge and sound module removed I can not get it to consistently start up in the same way. I am not sure if this is because the SNES is very broken or I am using the logic analyzer incorrectly. The SNES is currently configured with the lockout chip enabled but the reset signal from the PPU chips is disconnected from the rest of the system. The reset line for the rest of the system is pulled up by a 100K resistor and monitored by a brownout detection chip. Got any ideas as to where to go from here? If you want I can post screen caps from my logic analyzer and an entire ascii dump of the 8K of data that it has captured. I do find it weard that the address lines show activity even before the sysclock output of the cpu has become active.

author: poot36
author_rank: Frequent Contributor
timestamp: August 10, 2015, 06:23:27 am
content: This topic has been continued on the nesdev forum under the user name Poot36. Link here:http://forums.nesdev.com/viewtopic.php?t=13088