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Fixing up a SMS2 - Restarting after SEGA logo.
Post Posted: Fri Oct 25, 2019 7:53 am
Last edited by Insomniac on Tue Oct 29, 2019 2:45 pm; edited 1 time in total
Hi all!

I have recently picked up an old Pal-I MasterSystem2 on ebay, that was known not to work. It has the exact issue mentioned in this post here:

/forums/14339-MasterSystemIIUnableToBootUp

(I cant post links yet)

I have opened it up and given it a good clean, and I cannot see any broken traces, though I am currently working my way across the board checking.

However, there is one obvious issue with the "Noise Cancelling" inductor at FB7. It is raised off the board at an angle and some goop has come out of it. Checking its resistance, it is at 0 Ohms, so presumably shorted internally.

My question I guess is, does anyone know what I can replace this with, I cannot find any specs for it, or even any that have the same package!
I have checked the docs on here, but while they have info on other components there's nothing on this one.

I have taken a picture of it, but don't have it on me right now, so will post it later on when I do.

Thanks for any help, it would be great to get another SMS back up and running again!
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Post Posted: Fri Oct 25, 2019 8:04 am
Here is the pic.
20191024_155750.jpg (3.89 MB)
20191024_155750.jpg

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Post Posted: Fri Oct 25, 2019 8:49 am
That part is perfectly fine. Its just a couple of turns on wire on a ferrite bead. If it were open that would be a problem but being close to 0 ohms is expected. The goo is just glue that they have used to keep it from flopping about and breaking loose.
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Post Posted: Fri Oct 25, 2019 1:37 pm
wasup wrote
That part is perfectly fine. Its just a couple of turns on wire on a ferrite bead. If it were open that would be a problem but being close to 0 ohms is expected. The goo is just glue that they have used to keep it from flopping about and breaking loose.


Damn, I was hoping it was that simple! I guess I will just reseat that one and go over the board trace by trace. If any one knows which area is the most likely cause for a system that resets repeatedly at the sega logo it would be much appreciated!
Thanks for the help so far :-)
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Fixing up a SMS2 - Inductor FB7 Replacement?
Post Posted: Fri Oct 25, 2019 4:29 pm
From the description it sounds like the software is continuously restarting or rebooting rather than being reset. Reset problems usually stop boot up all together or are more erratic than cyclic.

Check the continuity of the Address lines between the CPU and the System ROM, System RAM and the Cart slot with your multimeter. Start with the highest one (A15) and work your way down (A14, A13, A12...). Schematics and pinouts are available in the Development pages of SMSPower.

If the Address lines all test OK then I would check the data and control lines in this area as well.

If all the lines test OK, you may have a faulty ROM or RAM chip. Both are replaceable, but it's more work.
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Post Posted: Sun Oct 27, 2019 9:45 am
asynchronous wrote
From the description it sounds like the software is continuously restarting or rebooting rather than being reset. Reset problems usually stop boot up all together or are more erratic than cyclic.

Check the continuity of the Address lines between the CPU and the System ROM, System RAM and the Cart slot with your multimeter. Start with the highest one (A15) and work your way down (A14, A13, A12...). Schematics and pinouts are available in the Development pages of SMSPower.

If the Address lines all test OK then I would check the data and control lines in this area as well.

If all the lines test OK, you may have a faulty ROM or RAM chip. Both are replaceable, but it's more work.


Thanks for the info! I have just started going through these with the service doc up, and a number of the pins don't seem happy, either not showing a connection or having high resistance. (Assuming I am actually testing the correct pins!)

There doesn't seem to be any problems on the bottom of the board though, all those traces seem ok. Do I now need to remove the chips to look at the traces running under them, or is there a better way to go about it?
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Post Posted: Sun Oct 27, 2019 12:44 pm
Just realised that the pins in the diagram aren't actually in the right order... urgh.
In the mean time I have removed and put back in the Z80... all fine under there.
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Fixing up a SMS2 - Inductor FB7 Replacement?
Post Posted: Sun Oct 27, 2019 1:28 pm
No need to remove the chips, just measure the resistance from one point to the other.
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Post Posted: Sun Oct 27, 2019 2:18 pm
asynchronous wrote
No need to remove the chips, just measure the resistance from one point to the other.


Thanks for the help so far!

So , I have tested all the address and data pins between IC's 1, 2, 3 and 4, all seem OK so far as I can tell. Haven't finished going over the cart slot, though I would have thought that can't be relevent when booting without a cart?

Which pins are the control lines?

Thanks!
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Post Posted: Sun Oct 27, 2019 6:18 pm
I assume the RAM is IC3? These seem fairly easy to find on ebay, but if it is the ROM that is dead, is there somewhere that sells them, or will I need another broken console? I haven't had any luck finding them anywhere.
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Post Posted: Sun Oct 27, 2019 8:22 pm
Insomniac wrote
I assume the RAM is IC3? These seem fairly easy to find on ebay, but if it is the ROM that is dead, is there somewhere that sells them, or will I need another broken console? I haven't had any luck finding them anywhere.


You would have to get the BIOs rom online and burn your own using an eprom and eprom burner.
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Post Posted: Sun Oct 27, 2019 11:13 pm
IllusionOfMana wrote
Insomniac wrote
I assume the RAM is IC3? These seem fairly easy to find on ebay, but if it is the ROM that is dead, is there somewhere that sells them, or will I need another broken console? I haven't had any luck finding them anywhere.


You would have to get the BIOs rom online and burn your own using an eprom and eprom burner.


An sms2 will likely have the alex the kidd or sonic bios.. both have a built in mapper and you wont be able to just write that to an eprom/flash chip and have it work. If you need to replace it i suggest using either the jp bios or snail maze bios as these wont require a mapper and can be written to an eprom/flash chip and work fine
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Post Posted: Mon Oct 28, 2019 3:03 am
wasup wrote

An sms2 will likely have the alex the kidd or sonic bios.. both have a built in mapper and you wont be able to just write that to an eprom/flash chip and have it work. If you need to replace it i suggest using either the jp bios or snail maze bios as these wont require a mapper and can be written to an eprom/flash chip and work fine


Right I forgot about that. my vote is for snail maze bios, best game on earth imo.
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Post Posted: Mon Oct 28, 2019 4:03 am
IllusionOfMana wrote
Right I forgot about that. my vote is for snail maze bios, best game on earth imo.


Totally agree there!
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Post Posted: Mon Oct 28, 2019 7:28 am
Thanks for all the info!

Would this chip work?

https://www.ebay.com/c/626116661

If not I guess I will another broken sms or save up for a eprom programmer.
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Post Posted: Mon Oct 28, 2019 1:36 pm
Oh, I also spotted this article:

http://www.smspower.org/Development/BIOSRemoval

Would that be a potential work around? I get the Sega logo, so presumably some part of the BIOS is functioning?
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Post Posted: Mon Oct 28, 2019 10:15 pm
You could give that a go.. would rule out the bios.
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Post Posted: Tue Oct 29, 2019 8:56 am
Ok, I have ordered that replacement ROM chip and some sockets so I don't have to work too much on the board itself which is a little... fragile when it comes to desoldering.

If the new chip does indeed work, I may try the old one with that mod just to see if it is a viable fix for anyone that has the same problem in the future.

Fingers crossed!
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Fixing up a SMS2 - Inductor FB7 Replacement?
Post Posted: Tue Oct 29, 2019 12:50 pm
The BIOS you have ordered (MPR-11458) is a US/European BIOS v3.4 with Hang On built-in and 128KB in size. While it's on its way it wouldn't be a bad idea to search the MPR number on the BIOS in your SMS2. If your BIOS is also a 128KB BIOS then I don't think there will be any problems with a swap. However if the chip different size I would double check the pinouts are identical between the 2 chips. Some SMS have jumpers hardwired into the PCB tracks set for different BIOS ROMs. For the price you can't go wrong and it will confirm or rule out the BIOS chip as faulty.

It wouldn't be a bad idea to test the continuity for the remaining pins for the BIOS and RAM which are the control lines (/CE, /EXM, /RD, /WR, /Refrsh). Can I also ask if you checked the power supply to these chips for a firm 5 volts?
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Post Posted: Tue Oct 29, 2019 2:06 pm
Yeah, the current one is a MPR-12808, which should be the Alex Kidd one and is the same size. I checked that I was getting 5v on the regulator's output but haven't checked what it is at the chips.

I will go over the other pins tonight when I get a chance :)

Thanks!
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Post Posted: Sat Nov 02, 2019 11:49 am
Ok, we have progress!

The new BIOS chip arrived today, I got the old chip out and replaced it with a socket. (The traces are so week, a few lifted and I had to epoxy them back down, but all ok with continuity so far).

With the new chip in place I can get hang-on up and running. It happily will go from title screen to demo mode, so big improvement there!

Unfortunately I cannot get it to boot from game cartridge yet, and get no response from a megadrive pad (Should those work?).

So time to check some more traces I guess and see if I can clean out the slot a bit more.
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Fixing up a SMS2 - Restarting after SEGA logo.
Post Posted: Sat Nov 02, 2019 2:10 pm
Nice. "Improvement" is an understatement. You've got a non-booting console running again.

The first thing to do for cartridges not loading is clean the cartridge PCB edge and the cartridge connector. Plain old paper is good for this. It's grippy enough to remove dirt and tarnish but not abrasive to remove any coating. Fold the paper over and over until it's about the thickness of the cart PCB and insert it and remove it in and out of the connector repeatedly. For the cart PCB edge you can rub it with a pencil eraser to clean it, or paper again, or use a solvent. Once both are cleaned try the cartridge again.

A Megadrive controller will work fine. Buttons 1 and 2 become buttons B and C on the Megadrive controller. There's a few causes for a non-responsive controller. Checking the continuity of the lines between the controller ports and IC4 is a good start.
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Post Posted: Sun Nov 03, 2019 3:27 pm
I also have an SMS II with this behaviour, i have socketed the Z80, Bios and Ram and verified continuity with all pins.

I have checked the the cart slot has continuity to the Z80 using the attached pinout.

I have swapped the bios chip for a known working Alex Kidd, issue remains.

I'm now stuck on where to check next?
pinouts-exportsms.png (12.73 KB)
pinouts-exportsms.png

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Fixing up a SMS2 - Restarting after SEGA logo.
Post Posted: Mon Nov 04, 2019 2:14 am
You could have faulty RAM Chip if continuity all checks out and the BIOS has been eliminated as a fault.

Unfortunately you guys are both getting to the point where remote assistance is reaching its limit and special tools are needed to diagnose what's happening, in particular, when the restart occurs. I have an oscilloscope for this but not everyone has one of these laying around.

Here's the order in which I generally diagnose a faulty console that doesn't boot or run right. It's very similar to the suggested procedure in the service manual. I use an oscilloscope for most of these because a DMM is generally not fast enough. If you haven't covered all of these I suggest doing what you can on each.

0) Visual inspection
Goes without saying, but it helps to know what to look for. Clean the cartridge connector and also the cartridge edge. Always try a few different cartridges. Also check if any chips are getting hot to the touch during operation.

1) Check the power rail (5V DC)
We're looking for a firm 5.0V or very close to it which doesn't dip or fluctuate during operation to every chip - including the Cartridge ROM. It's a good idea to also check the ground connections on each chip as well.

2) Check the reset line to each chip.
After a short, initial period of being at 0V the reset line should go to 5.0 and stay there.

3) Check the clock signals
For the SMS2 the clock starts at IC4 and is fed to IC5 (VDP/PSG) and IC1 (CPU)

4) Check Refresh, CE and OE signals for activity
Check these signals for activity for the BIOS, RAM and Cartridge ROM. For the RAM also check WR.

5) Check Address lines, Data lines, and control lines continuity between the CPU, BIOS, RAM, and cartridge ROM.
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Post Posted: Mon Nov 04, 2019 8:21 am
Thank you so much for all the help, its been really helpful! :)

I will see if anyone at work has an oscilloscope I can borrow (always worth an ask!).

Since my last post I have check continuity between the inside of the cart and the base of the slot connector, and all pins seem fine now. I have also checked between the player 1 controller pins and IC4, which all seem good too.

My guess would be that IC4 is also misbehaving given that I have two issues that relate to that chip, but I will keep checking the rest of the points you have listed where I can.

For scrappy, I found this on ebay which I was planning on picking up if the ROM change hadn't worked for me:
https://www.ebay.co.uk/itm/274054184132
May be worth a shot if you have already swapped out the ROM but not the RAM.
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Post Posted: Tue Nov 05, 2019 9:00 pm
I have found 2 "untested" mastersystems on ebay. So I may just swap out the IC4 from one that works (assuming one does!) to rule that out if I cant find anything by the time they turn up. Obviously, if one of those works I don't *need* to fix this one, but I would really like to know whats up with it now!
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Fixing up a SMS2 - Restarting after SEGA logo.
Post Posted: Wed Nov 06, 2019 12:58 pm
Yes, closure is a beautiful thing.

I've been thinking about this. With all the continuity checked, BIOS replaced, and RAM possibly OK, I’m beginning to think this could be that IC4 is damaged in some way that writes to Port 3E and reads from ports DC and DD are not working. I can’t tell for certain without using an oscilloscope to check all the CE lines and OE lines for activity.

I tried a couple of tests on my SMS with an MPR-11458 BIOS. The MPR-11458 BIOS will display the Software Error message for an inserted cartridge when the checksum is bad or the region isn’t right. But when the licence string on a cartridge ROM isn’t valid, the Software Error message isn’t displayed. Instead, the built-in game (Hang On) is loaded.

Now, if writes to port 3E are not working, the BIOS will never be mapped out and the cartridge will never be mapped in. If this is the case, when the BIOS checks the cartridge ROM for a licence string, it will actually be reading itself. The MPR-11458 BIOS doesn’t have a valid licence string at 7FF0 so the BIOS will think there’s no cartridge present and....load the built-in game.

So with that said, here are some tests you can do on IC4 with just a multimeter:

If you haven't already tested the power rails and Reset lines on IC4 are all good and stable at 5.0 volts or very close to 5.0 volts, do that first.

Next, check the continuity of the CPU lines responsible for IO reads and IO writes between the CPU and IC4. These are A0, A6, A7, /IORQ, /WR, /RD, and D0-D7.

The KILLGA input, which is pin 1 on the 315-5237, should measure 0 Volts when the console is powered. Try grounding the KILLGA pin and powering on the console to see if it makes a difference even if the reading is good maybe?

When all the controller port lines are configured as inputs by software, these pins on IC4 (315-5237) with nothing connected to the controller ports will measure 5 volts DC when the console is powered.

Let us all know how you go.
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Post Posted: Fri Nov 08, 2019 9:36 pm
Hi!

Ok, I have some... odd results.

I have tested all 0v and 5v lines on IC4, and the look good, sitting at 4.99v.

All continuity on the lines you mentioned at ok.

However, while all the other CN2-X (10-23) read at somewhere near-ish to 5v (~4.9) pin 11 is at 0.3v.

However what is the weirdest is playing with pin 1.
Shorting it down to 0v didnt seem to make any difference. However when I ran continuity from it to gnd while it was running, it behaved like a button was pressed and started the game, and would even drive the bike forward.

Shorting it to the pin next to it on the board could also get it to start the game, though was unable to drive the bike. Unfortunately, neither of these actually allowed the controller to work.

I am going to see whats going on with pin 11.
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Post Posted: Sat Nov 09, 2019 7:47 am
I can't see anything wrong with continuity from pin 11, presumably its an output as it doesn't seem to go anywhere other than the controller port and ground. So it's just not outputting anything for some reason :s
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Post Posted: Sat Nov 09, 2019 3:57 pm
I think you have confirmed that IC4 is damaged internally I'm afraid.

Pin 11 is Player 1 Down. It's an input only pin. If it's not measuring 5V when the console powered up then the internal pull up resistor on that pin is stuffed.

For pin 1, you can't measure continuity when the console is powered up. I'm guessing doing that made the pin go high disabling the chip and floating the data bus on a port DC read giving random buttons pressed.
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Post Posted: Sat Nov 09, 2019 4:07 pm
Yeah, I was aware you can't read continuity while it was running, not entirely sure what I was expecting from it to be honest!

I am expecting the other two consoles in the next few days, hopefully I can at least get a few of them working!
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Post Posted: Mon Nov 11, 2019 3:50 pm
The other two SMS2's have just turned up.

They are... disgusting to be honest! Full of dust and rust for the most part.

One of them didn't turn on initially, but after poking at it with the multi-meter it did, so I think its just dusty contacts in the barrel connector.

The other turned on right away, but showed a very distorted picture for a few minutes until it had warmed up, presumably something not quite right with the RF unit.

I think I will try swapping out the IC4 from the second one as its not quite right already and my first one is in better condition overrall, and see what happens.
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Post Posted: Fri Nov 15, 2019 11:15 pm
Ok, bit of an update.

I managed to swap IC4 on the two consoles. And it made no difference. Still no cart boot and no input.

So, out of interactive tried the bad chip in the good board, and it worked fine with the expected fault we detected, down button was being randomly pressed.

This board is really struggling to stay intact with all the desoldering so I think I will keep one of the others in the long run. But no idea why this is not working at this point...
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Fixing up a SMS2 - Restarting after SEGA logo.
Post Posted: Sat Nov 16, 2019 12:06 pm
So it's an issue with the board. And testing with just a multi-meter hasn't been able to isolate the fault.

I think you've reached the limit of fault finding without better test gear. Nonetheless, with the 3 consoles you bought you will end up with at least one fully working SMS II and a good cache of spare parts as well. Not a bad result at all.

Now...if we can all silence the intrigue. :)
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Post Posted: Sat Nov 16, 2019 1:34 pm
Yeah, I've picked one out I will keep. I will probably sell the other working one off and hold on to the mystery board for a bit and keep poking at it, maybe I will re-cap it for fun at some point, it certainly seems like the obvious contenders are all working at this point.

Thanks for all the help and info, it's been really interesting to learn a bit more about the SMS, if I ever work anything out with it I will post an update!
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