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Hello!

So I've got hold of two faulty SMS 2s (IC BD M4Jr. PAL) - the first I managed to fix was a dodgy controller port.. the other is proving more difficult. Switched on, with no game - it just shows a black screen, no SEGA Logo, or sign of Alex Kidd (I don't know if all these models had that?)

If plug in a game cartridge (in this case an Everdrive type guy) - which works perfectly on the other SMS 2 - I get this glitchy graphic on the screen for a bit (attached), then it changes to more of the random squares, and sorta repeats itself. I've had a quick once over with the thermal imaging camera - only thing getting super warm is the voltage regulator, but it's kicking out a steady 5v. Everything else looks okay - I've given it a visual once over, and everything looks pretty good.

I have never looked at one of these before, and don't really know where best to start.. I'll check the voltages to all the ICs, and the traces. I could maybe start swapping out the VRAM and VDP from my working model, but I don't want to do it unnecessarily, heck it could maybe even be the CPU?

I just thought I'd check on the hive mind of SMS Power for a decent starting point!

Thanks

Kip

Screenshot 2024-12-01 185310.jpg (69.24 KB)

Screenshot of Corruption

Screenshot 2024-12-01 185232.jpg (32.64 KB)

Alternate Corruption

I have no idea why is happening in your case. However I think you may have faulty VRAM. That's the very first thing that comes into mind when seeing those patterns. However I could be wrong, I have never had to repair a Sega Master System. The most similar thing I repaired was a Neo Geo...

By the way, do you get audio? The SEGA Logo has audible tones.

If you hear nothing, then my first suspect would be the BIOS.

By the way, you should check this documentation https://www.smspower.org/Development/SegaMasterSystemIIServiceManual

Ahhhh thank you.. I must be honest, I hadn't been listening for sounds.. However, now with volume up, with no cartridge in, I can HEAR Alex Kidd.. So your hunch about VRAM could well be correct!

Thank you - now I need to see if I can still buy that!

Kip

Let's hope it is VRAM. Otherwise the VDP could be compromised, which means the machine could only be used as a spare unit.

As for the SRAM, with a few small mods I think you could use a common 6264 or even if you can't find one you could try a 62256 (or any 32KB compatible SRAM) to replace it.

VRAM in SMS is made out of PSRAM that NEC calls XRAM. It latches address bus with its access stobes which allows the same lines on VDP also to be used for data so a normal SRAM cannot be used.

TmEE wrote

VRAM in SMS is made out of PSRAM that NEC calls XRAM. It latches address bus with its access stobes which allows the same lines on VDP also to be used for data so a normal SRAM cannot be used.

In the SMS II the refresh signal is always held high. But I guess it may be as you say. I may take the opportunity to design a proper replacement.

==== EDIT ====
You are right. SMS2 VDP memory accesses are 16 bit width. If using a latch and an inverter it would be possible to use a standard SRAM. I could design and construct such a patch.

I just checked the datasheet, the memories latch address when !CE goes low. Refresh signal is not part of the process.

To use SRAM, an address latch needs to be added which does the same stuff, since address and data both come from the same 16 lines from VDP, not unlike NES PPU. EDIT: I saw your edit lol

This is a quick and dirty drawing I made. Combined with a connector with the pinout of the replaced memory, it should allow replace it with normal SRAMs ranging from 8KB to 32KB, which are easy to source.

In case you cannot source the required part you can recur to this circuit.

@TmEE I guess we wrote it at the very same time! :)

SMS2_SRAM.png (45.6 KB)

Wow.. you guys think I'm a lot smarter than I actually am. Thank you!

I actually make videos on YouTube where I try and fix stuff and teach myself (and hopefully others) how to do it.. I think the VRAM is a great starting point, so I'm going to desolder it from my working SMS2 and swap it onto the faulty board (I've ordered some sockets too so I don't have to keep on desoldering and resoldering). That way I can know for sure if it's the VRAM, or something else..

Will report back with my findings!

Thanks

kip

Bits Passats wrote

This is a quick and dirty drawing I made. Combined with a connector with the pinout of the replaced memory, it should allow replace it with normal SRAMs ranging from 8KB to 32KB, which are easy to source.

In case you cannot source the required part you can recur to this circuit.

@TmEE I guess we wrote it at the very same time! :)

You want to use 2 x 74'373 which is a transparent latch instead of 74'273 or 74'374 which are edge triggered devices so you don't need an inverter on the /CE line. I have a schematic of this.....somewhere.

@Kip, it would be a good idea to check the VRAM bus between the VDP and VRAM for broken or bridged lines before desoldering chips from the board. The SMS board pads and traces are fragile.

asynchronous wrote

You want to use 2 x 74'373 which is a transparent latch instead of 74'273 or 74'374 which are edge triggered devices so you don't need an inverter on the /CE line. I have a schematic of this.....somewhere.

I will have your suggestion in account and will consider it.

Thank you very much

if you can get to run software from your EverDrive, you could try memtest

I expect the RAM test to pass, then you press a button and VRAM tests are performed. If you then see any red letter on the screen then it's confirmed. I expect that to be your issue, hard to tell if a RAM chip has failed or something else though.

sverx wrote

if you can get to run software from your EverDrive, you could try memtest

I expect the RAM test to pass, then you press a button and VRAM tests are performed. If you then see any red letter on the screen then it's confirmed. I expect that to be your issue, hard to tell if a RAM chip has failed or something else though.

Weirdly... I think, now I can hear the music, I don't think it's actually loading the cartridge at all, when the cartridge is plugged in, it just seems to load into Alex Kidd.. (Well it's playing the music for it!)

That’s not unusual, it will boot the built in game if the cartridge slot read fails which can just be because of dirt or oxidation.

But that implies two different issues. One probably with the connector and another with the video subsystem.

I don't think it to be work RAM. However that could be easily tested as the 8KB RAM IC used can be swapped with a regular SRAM one. Then you would have a spare 4168 to use at the VRAM, you have only to determine which is the one that is failing.

About the connector, try cleaning it. If it still does not work, try replacing it. This part is still in production so you shouldn't have any problem.

==== EDIT ====

What column is failing to be rendered, the odd or the even one? The answer to this question might give you a clue.

kiph wrote

it just seems to load into Alex Kidd.. (Well it's playing the music for it!)

so the RAM is likely to be just fine, and the CPU is running. I keep suspecting the VRAM, but clearly there's another issue too if it doesn't start a game from the cartridge.

Bits Passats wrote

What column is failing to be rendered, the odd or the even one? The answer to this question might give you a clue.

uhm, doesn't appear to always be the same one. Also, each entry in the background map is 16 bits wide so it should use both chips for every entry... and on top of that, the problem might be in the traces instead of being in the chips.

Sooo - to update you all a little - I've made a bit of progress - ISH.

So my brain completely forgot about that Sanyo chip up near the CPU being RAM.. So I was under the impression that the 2 x NEC RAM chips were the SRAM and VRAM - So I desoldered the two NEC RAM chips, fitted a socket for both, and switched them around (seeing if the fault would move,or change) It didn't - either way around, the fault persisted and looked identical. If there had been a difference I'd have probably desoldered the NEC chips from my other SMS2 and tried those..

I've tested continuity on the VRAM to the VDP, and the VDP to the CPU - all looks okay..

Is it worth me swapping out the Sanyo RAM chip to see if that could be faulty? Or do we think this is still pointing at the VDP?

I don't have a Logic Probe or Oscilloscope, so I can't go too deep into the troubleshooting steps.. It's all making for an interesting video, but I'd love to fix it!

Kip

What are the references (as on the board and the schematics) of the ICs you changed? Without you telling us what chips exactly you touched, we cannot help you.

Given how fine is the game playing except for the graphics aspect, I guess if the VRAM is fine, then the VDP is faulty. I am sorry, the VDP is an ASIC, which means the only reliable source is other SMS2. If that was the case you should use that SMS2 as a spare machine.

But first, please tell us what memories have you exchanged, please.

So for clarity, the chips I swapped around were IC 6 and IC 7 (both NEC D4168C-15-SG) - I DID think that swapping them around made no difference..

HOWEVER, now I'm actually watching back and syncing up the screen capture I took before and after swapping the RAM it seems there IS a very subtle difference between the two. I've attached a few side by side comparisons.. on a brief glance, they look identical.. however, there is a difference. So I wonder if the VRAM IS faulty? Although I don't know if it's a big enough difference to confirm it.

Vlog 513 - Master System 2 - Part 2.00_22_53_13.Still100.jpg (397.99 KB)

Side by Side Comparison 1

Vlog 513 - Master System 2 - Part 2.00_23_30_15.Still101.jpg (653.43 KB)

Side by Side Comparison 2

Swapping VRAM chips (i.e. IC6 <-> IC7) didn’t make any real difference from the photos.

It sounds like this is a later SMS2 with a Sanyo SRAM chip for work ram instead of a 4168 XRAM chip. The Sanyo SRAM won’t work as VRAM.

There are still a few things to test and check before concluding that the VDP or VRAM are faulty.

You can clean the cartridge slot connector by repeatedly folding a piece of plain white paper to the thickness of cartridge circuit board and inserting it in and out of the connector a few times. When the connector is clean, cartridges will make a sort of “thuck” sound when they are inserted into the connector. This cleaning usually gets cartridges working again.

asynchronous wrote

Swapping VRAM chips (i.e. IC6 <-> IC7) didn’t make any real difference from the photos.

It sounds like this is a later SMS2 with a Sanyo SRAM chip for work ram instead of a 4168 XRAM chip. The Sanyo SRAM won’t work as VRAM.

There are still a few things to test and check before concluding that the VDP or VRAM are faulty.

You can clean the cartridge slot connector by repeatedly folding a piece of plain white paper to the thickness of cartridge circuit board and inserting it in and out of the connector a few times. When the connector is clean, cartridges will make a sort of “thuck” sound when they are inserted into the connector. This cleaning usually gets cartridges working again.

The OP has an issue with the on-board game. It is not the CPU, the ROM or the work RAM. What else could be?

Hopefully this will put everything into a bit of perspective, I've edited everything I've done into a video on my YouTube channel
here.

Hopefully it helps!

Props for naming the forum.

From the audio it sounds like there's an issue with one or two data bus lines between IC5 and the CPU. An issue with the CPU data bus to IC5 will mean audio and video data will not be transferred to IC5 and VRAM correctly. It could be a broken line, a bridged line, or IC5.

Good luck.

just saw the video: the fact that some of the notes in the Alex Kidd tune are clearly wrong, kind of moves the issue away from the video RAM, as the VDP chip doesn't use video RAM at all for the music.

The fact that the CPU can still send data to the VDP, but the data seems to be wrong sometimes, makes what asynchronous just said above a very likely possibility. Check continuity on the data lines from the CPU to the VDP.

edit: also the fact that the BIOS doesn't start the cartridge when inserted it likely means that the CPU is reading wrong data from there, again points to an issue with the data bus, but the CPU seems to be reading the program from the BIOS correctly, so I'd say the issue is far from the CPU and BIOS chip and closer to the VDP and cartridge slot part of the board.

My bet? A broken trace below the cartridge slot, because someone pushed down quite hard on it.

Author	Message
kiph Joined: 01 Dec 2024 Posts: 7	Faulty SMS 2 - Boots with Graphical Glitches Posted: Sun Dec 01, 2024 7:19 pm
kiph Joined: 01 Dec 2024 Posts: 7	Hello! So I've got hold of two faulty SMS 2s (IC BD M4Jr. PAL) - the first I managed to fix was a dodgy controller port.. the other is proving more difficult. Switched on, with no game - it just shows a black screen, no SEGA Logo, or sign of Alex Kidd (I don't know if all these models had that?) If plug in a game cartridge (in this case an Everdrive type guy) - which works perfectly on the other SMS 2 - I get this glitchy graphic on the screen for a bit (attached), then it changes to more of the random squares, and sorta repeats itself. I've had a quick once over with the thermal imaging camera - only thing getting super warm is the voltage regulator, but it's kicking out a steady 5v. Everything else looks okay - I've given it a visual once over, and everything looks pretty good. I have never looked at one of these before, and don't really know where best to start.. I'll check the voltages to all the ICs, and the traces. I could maybe start swapping out the VRAM and VDP from my working model, but I don't want to do it unnecessarily, heck it could maybe even be the CPU? I just thought I'd check on the hive mind of SMS Power for a decent starting point! Thanks Kip Screenshot 2024-12-01 185310.jpg (69.24 KB) Screenshot of Corruption Screenshot 2024-12-01 185232.jpg (32.64 KB) Alternate Corruption

Bits Passats Joined: 14 Feb 2024 Posts: 42 Location: Andorra	Posted: Mon Dec 02, 2024 8:13 am
	I have no idea why is happening in your case. However I think you may have faulty VRAM. That's the very first thing that comes into mind when seeing those patterns. However I could be wrong, I have never had to repair a Sega Master System. The most similar thing I repaired was a Neo Geo... By the way, do you get audio? The SEGA Logo has audible tones. If you hear nothing, then my first suspect would be the BIOS. By the way, you should check this documentation https://www.smspower.org/Development/SegaMasterSystemIIServiceManual

kiph Joined: 01 Dec 2024 Posts: 7	Posted: Mon Dec 02, 2024 9:11 am
kiph Joined: 01 Dec 2024 Posts: 7	Ahhhh thank you.. I must be honest, I hadn't been listening for sounds.. However, now with volume up, with no cartridge in, I can HEAR Alex Kidd.. So your hunch about VRAM could well be correct! Thank you - now I need to see if I can still buy that! Kip

Bits Passats Joined: 14 Feb 2024 Posts: 42 Location: Andorra	Posted: Mon Dec 02, 2024 9:24 am
	Let's hope it is VRAM. Otherwise the VDP could be compromised, which means the machine could only be used as a spare unit. As for the SRAM, with a few small mods I think you could use a common 6264 or even if you can't find one you could try a 62256 (or any 32KB compatible SRAM) to replace it.

TmEE Joined: 31 Oct 2007 Posts: 855 Location: Norway (used to be Estonia)	Posted: Mon Dec 02, 2024 9:31 am
	VRAM in SMS is made out of PSRAM that NEC calls XRAM. It latches address bus with its access stobes which allows the same lines on VDP also to be used for data so a normal SRAM cannot be used.

Bits Passats Joined: 14 Feb 2024 Posts: 42 Location: Andorra	Posted: Mon Dec 02, 2024 9:35 am
	TmEE wrote VRAM in SMS is made out of PSRAM that NEC calls XRAM. It latches address bus with its access stobes which allows the same lines on VDP also to be used for data so a normal SRAM cannot be used. In the SMS II the refresh signal is always held high. But I guess it may be as you say. I may take the opportunity to design a proper replacement. ==== EDIT ==== You are right. SMS2 VDP memory accesses are 16 bit width. If using a latch and an inverter it would be possible to use a standard SRAM. I could design and construct such a patch.

TmEE Joined: 31 Oct 2007 Posts: 855 Location: Norway (used to be Estonia)	Posted: Mon Dec 02, 2024 9:52 am
	I just checked the datasheet, the memories latch address when !CE goes low. Refresh signal is not part of the process. To use SRAM, an address latch needs to be added which does the same stuff, since address and data both come from the same 16 lines from VDP, not unlike NES PPU. EDIT: I saw your edit lol

Bits Passats Joined: 14 Feb 2024 Posts: 42 Location: Andorra	Posted: Mon Dec 02, 2024 10:29 am
	This is a quick and dirty drawing I made. Combined with a connector with the pinout of the replaced memory, it should allow replace it with normal SRAMs ranging from 8KB to 32KB, which are easy to source. In case you cannot source the required part you can recur to this circuit. @TmEE I guess we wrote it at the very same time! :) SMS2_SRAM.png (45.6 KB)

kiph Joined: 01 Dec 2024 Posts: 7	Posted: Mon Dec 02, 2024 10:49 am
kiph Joined: 01 Dec 2024 Posts: 7	Wow.. you guys think I'm a lot smarter than I actually am. Thank you! I actually make videos on YouTube where I try and fix stuff and teach myself (and hopefully others) how to do it.. I think the VRAM is a great starting point, so I'm going to desolder it from my working SMS2 and swap it onto the faulty board (I've ordered some sockets too so I don't have to keep on desoldering and resoldering). That way I can know for sure if it's the VRAM, or something else.. Will report back with my findings! Thanks kip

asynchronous Joined: 14 Aug 2000 Posts: 769 Location: Adelaide, Australia	Faulty SMS 2 - Boots with Graphical Glitches Posted: Mon Dec 02, 2024 11:46 am
	Bits Passats wrote This is a quick and dirty drawing I made. Combined with a connector with the pinout of the replaced memory, it should allow replace it with normal SRAMs ranging from 8KB to 32KB, which are easy to source. In case you cannot source the required part you can recur to this circuit. @TmEE I guess we wrote it at the very same time! :) You want to use 2 x 74'373 which is a transparent latch instead of 74'273 or 74'374 which are edge triggered devices so you don't need an inverter on the /CE line. I have a schematic of this.....somewhere. @Kip, it would be a good idea to check the VRAM bus between the VDP and VRAM for broken or bridged lines before desoldering chips from the board. The SMS board pads and traces are fragile.

Bits Passats Joined: 14 Feb 2024 Posts: 42 Location: Andorra	Posted: Mon Dec 02, 2024 12:07 pm
	asynchronous wrote You want to use 2 x 74'373 which is a transparent latch instead of 74'273 or 74'374 which are edge triggered devices so you don't need an inverter on the /CE line. I have a schematic of this.....somewhere. I will have your suggestion in account and will consider it. Thank you very much

sverx Joined: 05 Sep 2013 Posts: 3996 Location: Stockholm, Sweden	Posted: Mon Dec 02, 2024 4:13 pm
	if you can get to run software from your EverDrive, you could try memtest I expect the RAM test to pass, then you press a button and VRAM tests are performed. If you then see any red letter on the screen then it's confirmed. I expect that to be your issue, hard to tell if a RAM chip has failed or something else though.

kiph Joined: 01 Dec 2024 Posts: 7	Posted: Mon Dec 02, 2024 5:02 pm
kiph Joined: 01 Dec 2024 Posts: 7	sverx wrote if you can get to run software from your EverDrive, you could try memtest I expect the RAM test to pass, then you press a button and VRAM tests are performed. If you then see any red letter on the screen then it's confirmed. I expect that to be your issue, hard to tell if a RAM chip has failed or something else though. Weirdly... I think, now I can hear the music, I don't think it's actually loading the cartridge at all, when the cartridge is plugged in, it just seems to load into Alex Kidd.. (Well it's playing the music for it!)

Maxim Site Admin Joined: 19 Oct 1999 Posts: 15005 Location: London	Posted: Mon Dec 02, 2024 5:46 pm
	That’s not unusual, it will boot the built in game if the cartridge slot read fails which can just be because of dirt or oxidation.

Bits Passats Joined: 14 Feb 2024 Posts: 42 Location: Andorra	Posted: Tue Dec 03, 2024 7:55 am
	But that implies two different issues. One probably with the connector and another with the video subsystem. I don't think it to be work RAM. However that could be easily tested as the 8KB RAM IC used can be swapped with a regular SRAM one. Then you would have a spare 4168 to use at the VRAM, you have only to determine which is the one that is failing. About the connector, try cleaning it. If it still does not work, try replacing it. This part is still in production so you shouldn't have any problem. ==== EDIT ==== What column is failing to be rendered, the odd or the even one? The answer to this question might give you a clue.

sverx Joined: 05 Sep 2013 Posts: 3996 Location: Stockholm, Sweden	Posted: Tue Dec 03, 2024 3:18 pm
	kiph wrote it just seems to load into Alex Kidd.. (Well it's playing the music for it!) so the RAM is likely to be just fine, and the CPU is running. I keep suspecting the VRAM, but clearly there's another issue too if it doesn't start a game from the cartridge. Bits Passats wrote What column is failing to be rendered, the odd or the even one? The answer to this question might give you a clue. uhm, doesn't appear to always be the same one. Also, each entry in the background map is 16 bits wide so it should use both chips for every entry... and on top of that, the problem might be in the traces instead of being in the chips.

kiph Joined: 01 Dec 2024 Posts: 7	Posted: Fri Dec 06, 2024 4:47 pm
kiph Joined: 01 Dec 2024 Posts: 7	Sooo - to update you all a little - I've made a bit of progress - ISH. So my brain completely forgot about that Sanyo chip up near the CPU being RAM.. So I was under the impression that the 2 x NEC RAM chips were the SRAM and VRAM - So I desoldered the two NEC RAM chips, fitted a socket for both, and switched them around (seeing if the fault would move,or change) It didn't - either way around, the fault persisted and looked identical. If there had been a difference I'd have probably desoldered the NEC chips from my other SMS2 and tried those.. I've tested continuity on the VRAM to the VDP, and the VDP to the CPU - all looks okay.. Is it worth me swapping out the Sanyo RAM chip to see if that could be faulty? Or do we think this is still pointing at the VDP? I don't have a Logic Probe or Oscilloscope, so I can't go too deep into the troubleshooting steps.. It's all making for an interesting video, but I'd love to fix it! Kip

Bits Passats Joined: 14 Feb 2024 Posts: 42 Location: Andorra	Posted: Sat Dec 07, 2024 8:05 am
	What are the references (as on the board and the schematics) of the ICs you changed? Without you telling us what chips exactly you touched, we cannot help you. Given how fine is the game playing except for the graphics aspect, I guess if the VRAM is fine, then the VDP is faulty. I am sorry, the VDP is an ASIC, which means the only reliable source is other SMS2. If that was the case you should use that SMS2 as a spare machine. But first, please tell us what memories have you exchanged, please.

kiph Joined: 01 Dec 2024 Posts: 7	Posted: Sat Dec 07, 2024 5:20 pm
kiph Joined: 01 Dec 2024 Posts: 7	So for clarity, the chips I swapped around were IC 6 and IC 7 (both NEC D4168C-15-SG) - I DID think that swapping them around made no difference.. HOWEVER, now I'm actually watching back and syncing up the screen capture I took before and after swapping the RAM it seems there IS a very subtle difference between the two. I've attached a few side by side comparisons.. on a brief glance, they look identical.. however, there is a difference. So I wonder if the VRAM IS faulty? Although I don't know if it's a big enough difference to confirm it. Vlog 513 - Master System 2 - Part 2.00_22_53_13.Still100.jpg (397.99 KB) Side by Side Comparison 1 Vlog 513 - Master System 2 - Part 2.00_23_30_15.Still101.jpg (653.43 KB) Side by Side Comparison 2

asynchronous Joined: 14 Aug 2000 Posts: 769 Location: Adelaide, Australia	Faulty SMS 2 - Boots with Graphical Glitches Posted: Sun Dec 08, 2024 1:55 pm
	Swapping VRAM chips (i.e. IC6 <-> IC7) didn’t make any real difference from the photos. It sounds like this is a later SMS2 with a Sanyo SRAM chip for work ram instead of a 4168 XRAM chip. The Sanyo SRAM won’t work as VRAM. There are still a few things to test and check before concluding that the VDP or VRAM are faulty. You can clean the cartridge slot connector by repeatedly folding a piece of plain white paper to the thickness of cartridge circuit board and inserting it in and out of the connector a few times. When the connector is clean, cartridges will make a sort of “thuck” sound when they are inserted into the connector. This cleaning usually gets cartridges working again.

Bits Passats Joined: 14 Feb 2024 Posts: 42 Location: Andorra	Posted: Tue Dec 10, 2024 8:34 am
	asynchronous wrote Swapping VRAM chips (i.e. IC6 <-> IC7) didn’t make any real difference from the photos. It sounds like this is a later SMS2 with a Sanyo SRAM chip for work ram instead of a 4168 XRAM chip. The Sanyo SRAM won’t work as VRAM. There are still a few things to test and check before concluding that the VDP or VRAM are faulty. You can clean the cartridge slot connector by repeatedly folding a piece of plain white paper to the thickness of cartridge circuit board and inserting it in and out of the connector a few times. When the connector is clean, cartridges will make a sort of “thuck” sound when they are inserted into the connector. This cleaning usually gets cartridges working again. The OP has an issue with the on-board game. It is not the CPU, the ROM or the work RAM. What else could be?

kiph Joined: 01 Dec 2024 Posts: 7	Posted: Fri Dec 27, 2024 6:39 pm
kiph Joined: 01 Dec 2024 Posts: 7	Hopefully this will put everything into a bit of perspective, I've edited everything I've done into a video on my YouTube channel here. Hopefully it helps!

asynchronous Joined: 14 Aug 2000 Posts: 769 Location: Adelaide, Australia	Faulty SMS 2 - Boots with Graphical Glitches Posted: Sat Dec 28, 2024 3:23 am
	Props for naming the forum. From the audio it sounds like there's an issue with one or two data bus lines between IC5 and the CPU. An issue with the CPU data bus to IC5 will mean audio and video data will not be transferred to IC5 and VRAM correctly. It could be a broken line, a bridged line, or IC5. Good luck.

sverx Joined: 05 Sep 2013 Posts: 3996 Location: Stockholm, Sweden	Posted: Sat Dec 28, 2024 3:47 pm
	just saw the video: the fact that some of the notes in the Alex Kidd tune are clearly wrong, kind of moves the issue away from the video RAM, as the VDP chip doesn't use video RAM at all for the music. The fact that the CPU can still send data to the VDP, but the data seems to be wrong sometimes, makes what asynchronous just said above a very likely possibility. Check continuity on the data lines from the CPU to the VDP. edit: also the fact that the BIOS doesn't start the cartridge when inserted it likely means that the CPU is reading wrong data from there, again points to an issue with the data bus, but the CPU seems to be reading the program from the BIOS correctly, so I'd say the issue is far from the CPU and BIOS chip and closer to the VDP and cartridge slot part of the board. My bet? A broken trace below the cartridge slot, because someone pushed down quite hard on it.

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