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Hi everyone,

I recently bought a faulty SG1000-II of Ebay with a faulty control unit. I tested it myself and indeed none of my controllers worked. Like nothing happened when I pressed the buttons; jiggling with the cables and connecters didn't seem to make a difference, nor pressing the buttons harder.

So I decided to open up the console and clean every part of the board. I tightened the pins of the cartridge slot as well; might as well do that when the console is opened up. Unfortunatily, the controllers still didn't work.

Because that didn't work, I decided to take a closer look at the board; I noticed that the contact points of the controller ports were almost entirely loose, so I restored the connections of the controller port and tested the console again. At first it appeared to work and I was playing some Hustle Chumy; great game by the way. But after barely 2 minutes of playing one of the D-pad buttons stopped working. Reseating the controller and restarting the console didn't make any difference. The more I played and the more I tried the more buttons stopped working till none of them worked anymore.

I thought I have just been careless at first and did the same procedure but paid more attention this time around. When I tested it; it worked again, but this time for barely 30 seconds. At some point of testing the game started doing weird stuff; like automatically pressing start at the title screen, but not responding to the controller at all. Sometimes it walkes all the way to the left when I don't press anything. Also when the controller isn't even plugged in, it does the same thing.

After this surprise I decided to check for continuity to verify that the connections are fine and they were fine. When I boot up the console after leaving it for a while it seems to work for a short time again, so maybe it is the CPU warming up just a tiny bit and then it stops working properly; which also tells me that a connection issue is not very likely to be the case. I'm not really all that familiar with the SG1000-II. I think however that the problem might be in the Sharp Z80A CPU; maybe it's faulty. I assume that the CU is part of the CPU like usual. Some of the pins of multiple chips have some rust on them, which I would normally say could result in connection issues, but it can't make the console do all kinds of random stuff, right?

Can any of you guys tell me what might be the problem with my console and how to fix it? Thanks a lot in advance and I'm looking forward to hearing from you soon,

Sincerely,

Miko, Strahssis

Doubtful it would be the CPU. Sounds more like a dry solder joint or a broken track on the board. It could also be a faulty pull-up resistor or I.C. Possibly temperature related. Photos would help. I take it it's not the your joypads because the fault is occurring whether the joypad is plugged in or not right?

The good news is that the controller circuit on the SG1000 to Mk3 is made up of discrete 74-series logic chip and external pull-up resistors. The bad news is that dry joints and broken tracks can be super difficult to find.

Perform some preliminary checks and measurements first:
Is the voltage regulator output measuring 5 Volts DC?
Is the voltage regulator heat sink is warm or hot to the touch?
Do the I.C.'s in the controller circuit have a good connection to the 5 Volt supply and gnd when powered?
Is the ground connection to the controller ports good?

Next try measuring the continuity between the controller ports, the pull-up resistors for the controller ports, and 74LS257 I.C.'s. When powered up, do the corresponding input pins on the 74LS257 I.C.'s follow the button presses on the joypad (i.e. 5 Volts when not pressed and 0 Volts when pressed)?

To check for dry joints and broken tracks, you will need a non-conducting object like a chopstick to poke around the board with and a non-conductive cold "sports" spray (it may be called something else in your part of the world).

Hi asynchronous,

Thank you for your reply, I really appreciate it! The joypads work fine on my other hardware so I'm pretty sure it's not the joypads.

I will post some pictures and a video below; I searched for the buttons on the IC, since I couldn't find a map on the internet. I also made notes of the voltages; the first number being the amount of volts when not doing anything and the second number being the amount of volts when pressing the corresponding button.

Wouldn't it be less time consuming to just reflow everything rather then looking over all the traces? Besides, if a trace is broken, there shouldn't be continuity to the ICs, but there is, so that wouldn't really make sense to me, right? Looking over the the issues you just said, I'm kinda thinking the faulty resistors might be the case here, but let me know what you think.

1) Yes, the Voltage Regulator outputs 5,00V exactly.
2) After a while it gets very hot; hot enough to burn my fingers if I'm not careful.
3) Yes, both the ICs and the controller ports have good connections with the GND and 5V.

Pictures: imgur(DOT)com(SLASH)a(SLASH)We9ra
Video: youtu(DOT)be(SLASH)H5CwFPMYcjc
Sorry, I'm not allowed to post links, so I will have to do it like this...

Thank you for your help and time and I'm looking forward to hearing from you soon!

Sincerely,

Miko, Strahssis

http://imgur.com/a/We9ra

Thank you Maxim! ;)

Quote

Wouldn't it be less time consuming to just reflow everything rather then looking over all the traces?

Sure, if you're keen to solder some more then go for it! If the problem is a dry joint then you'll fix it. If the problem is not a dry joint and a faulty track then the soldering won't do jack.

Quote

Besides, if a trace is broken, there shouldn't be continuity to the ICs, but there is, so that wouldn't really make sense to me, right?

Intermittent faults like what you're seeing can be difficult to find and can be subject to factors like temperature. That's where the chopstick and can of cold spray come in in narrowing down the fault.

You're on the right track though. Check the supply and ground. Check the signals. Reflow the joints. Check the resistors. Then contemplate next steps if none of that works. Without the console in front of me I can only help so much.

Thank you for your reply; I really appreciate it! Since I'm ill I haven't been able to work on it yet. As soon as I made some progress, I will let you know! ;)

asynchronous wrote

Quote

Wouldn't it be less time consuming to just reflow everything rather then looking over all the traces?

Sure, if you're keen to solder some more then go for it! If the problem is a dry joint then you'll fix it. If the problem is not a dry joint and a faulty track then the soldering won't do jack.

Quote

Besides, if a trace is broken, there shouldn't be continuity to the ICs, but there is, so that wouldn't really make sense to me, right?

Intermittent faults like what you're seeing can be difficult to find and can be subject to factors like temperature. That's where the chopstick and can of cold spray come in in narrowing down the fault.

You're on the right track though. Check the supply and ground. Check the signals. Reflow the joints. Check the resistors. Then contemplate next steps if none of that works. Without the console in front of me I can only help so much.

Today I spent half a day reflowing every single connection on the board. At first with some very nice succes; I was able to play games for at least 15 minutes; then I turned off the console to reassemble it again, and guess what; it didn't work anymore. However, it did work again a bit earlier this evening, but a few minutes ago it didn't work again. It appears to be completely random; the console only seems to work when it feels like doing so.

The symptoms are still pretty much the same; the game either controls itself; the controls are unresponsive or the controls are wrong; like when I press right, it jumps instead. Also interesting to point out is that only my Master System controller works; my Atari joypad, Genesis controller and the original SJ-152 don't work at all; with different symptoms.

Reflowing the connections I noticed that a few pins of multiple IC's had quiet a bit of rust on them. I did get continuity through them however and of course I cleaned them up for as much as possible.

Do you still think it could be a broken trace? Wouldn't a bad IC really not be an option? Maybe not the Z80, but those two connected to the controller ports. I'm far from an expert on this, but I have never seen bad or broken connections causing glitches like this; with bad connections it either works or doesn't, but not much in between; correct me if I'm wrong. Please let me know what you think is the next step; I will be working on it next week then!

You wouli want to run wires from the points of controller connectors to wherever the tracks end up, the machine uses a crappy single sided PCB and the ports are not going to be able to handle much mechanical stress at all. With wires the stress disappears into the wire and all the mechanical issues disappear.

It's possible it could be the logic IC's responsible for the controller ports. No harm in replacing those. These are the smaller chips approximately 1 cm x 2 cm;
74LS32,
74LS139,
74LS257 (there's 2 of these).

While you're at it replace the twelve 4.7k resistors as well.

But those symptoms you describe totally sound like track or solder faults, where it works fine and then intermittently stops working due to mechanical stress or temperature change etc. As I said these sort of faults can be hard to isolate and fix, even for people who have experience in electronics. That's what you're up against. You've got nothing to lose in trying to repair.

Author	Message
Strahssis Joined: 05 Mar 2018 Posts: 6 Location: Metropolis Zone	Repair -> SG1000-II faulty control unit! Posted: Mon Mar 05, 2018 11:56 am
	Hi everyone, I recently bought a faulty SG1000-II of Ebay with a faulty control unit. I tested it myself and indeed none of my controllers worked. Like nothing happened when I pressed the buttons; jiggling with the cables and connecters didn't seem to make a difference, nor pressing the buttons harder. So I decided to open up the console and clean every part of the board. I tightened the pins of the cartridge slot as well; might as well do that when the console is opened up. Unfortunatily, the controllers still didn't work. Because that didn't work, I decided to take a closer look at the board; I noticed that the contact points of the controller ports were almost entirely loose, so I restored the connections of the controller port and tested the console again. At first it appeared to work and I was playing some Hustle Chumy; great game by the way. But after barely 2 minutes of playing one of the D-pad buttons stopped working. Reseating the controller and restarting the console didn't make any difference. The more I played and the more I tried the more buttons stopped working till none of them worked anymore. I thought I have just been careless at first and did the same procedure but paid more attention this time around. When I tested it; it worked again, but this time for barely 30 seconds. At some point of testing the game started doing weird stuff; like automatically pressing start at the title screen, but not responding to the controller at all. Sometimes it walkes all the way to the left when I don't press anything. Also when the controller isn't even plugged in, it does the same thing. After this surprise I decided to check for continuity to verify that the connections are fine and they were fine. When I boot up the console after leaving it for a while it seems to work for a short time again, so maybe it is the CPU warming up just a tiny bit and then it stops working properly; which also tells me that a connection issue is not very likely to be the case. I'm not really all that familiar with the SG1000-II. I think however that the problem might be in the Sharp Z80A CPU; maybe it's faulty. I assume that the CU is part of the CPU like usual. Some of the pins of multiple chips have some rust on them, which I would normally say could result in connection issues, but it can't make the console do all kinds of random stuff, right? Can any of you guys tell me what might be the problem with my console and how to fix it? Thanks a lot in advance and I'm looking forward to hearing from you soon, Sincerely, Miko, Strahssis

asynchronous Joined: 14 Aug 2000 Posts: 742 Location: Adelaide, Australia	Repair -> SG1000-II faulty control unit! Posted: Mon Mar 05, 2018 2:32 pm
	Doubtful it would be the CPU. Sounds more like a dry solder joint or a broken track on the board. It could also be a faulty pull-up resistor or I.C. Possibly temperature related. Photos would help. I take it it's not the your joypads because the fault is occurring whether the joypad is plugged in or not right? The good news is that the controller circuit on the SG1000 to Mk3 is made up of discrete 74-series logic chip and external pull-up resistors. The bad news is that dry joints and broken tracks can be super difficult to find. Perform some preliminary checks and measurements first: Is the voltage regulator output measuring 5 Volts DC? Is the voltage regulator heat sink is warm or hot to the touch? Do the I.C.'s in the controller circuit have a good connection to the 5 Volt supply and gnd when powered? Is the ground connection to the controller ports good? Next try measuring the continuity between the controller ports, the pull-up resistors for the controller ports, and 74LS257 I.C.'s. When powered up, do the corresponding input pins on the 74LS257 I.C.'s follow the button presses on the joypad (i.e. 5 Volts when not pressed and 0 Volts when pressed)? To check for dry joints and broken tracks, you will need a non-conducting object like a chopstick to poke around the board with and a non-conductive cold "sports" spray (it may be called something else in your part of the world).

Strahssis Joined: 05 Mar 2018 Posts: 6 Location: Metropolis Zone	Posted: Mon Mar 05, 2018 9:10 pm
	Hi asynchronous, Thank you for your reply, I really appreciate it! The joypads work fine on my other hardware so I'm pretty sure it's not the joypads. I will post some pictures and a video below; I searched for the buttons on the IC, since I couldn't find a map on the internet. I also made notes of the voltages; the first number being the amount of volts when not doing anything and the second number being the amount of volts when pressing the corresponding button. Wouldn't it be less time consuming to just reflow everything rather then looking over all the traces? Besides, if a trace is broken, there shouldn't be continuity to the ICs, but there is, so that wouldn't really make sense to me, right? Looking over the the issues you just said, I'm kinda thinking the faulty resistors might be the case here, but let me know what you think. 1) Yes, the Voltage Regulator outputs 5,00V exactly. 2) After a while it gets very hot; hot enough to burn my fingers if I'm not careful. 3) Yes, both the ICs and the controller ports have good connections with the GND and 5V. Pictures: imgur(DOT)com(SLASH)a(SLASH)We9ra Video: youtu(DOT)be(SLASH)H5CwFPMYcjc Sorry, I'm not allowed to post links, so I will have to do it like this... Thank you for your help and time and I'm looking forward to hearing from you soon! Sincerely, Miko, Strahssis

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14741 Location: London	Posted: Mon Mar 05, 2018 9:56 pm
	http://imgur.com/a/We9ra

Strahssis Joined: 05 Mar 2018 Posts: 6 Location: Metropolis Zone	Posted: Mon Mar 05, 2018 10:08 pm
	Thank you Maxim! ;)

asynchronous Joined: 14 Aug 2000 Posts: 742 Location: Adelaide, Australia	Repair -> SG1000-II faulty control unit! Posted: Tue Mar 06, 2018 6:26 am
	Quote Wouldn't it be less time consuming to just reflow everything rather then looking over all the traces? Sure, if you're keen to solder some more then go for it! If the problem is a dry joint then you'll fix it. If the problem is not a dry joint and a faulty track then the soldering won't do jack. Quote Besides, if a trace is broken, there shouldn't be continuity to the ICs, but there is, so that wouldn't really make sense to me, right? Intermittent faults like what you're seeing can be difficult to find and can be subject to factors like temperature. That's where the chopstick and can of cold spray come in in narrowing down the fault. You're on the right track though. Check the supply and ground. Check the signals. Reflow the joints. Check the resistors. Then contemplate next steps if none of that works. Without the console in front of me I can only help so much.

Strahssis Joined: 05 Mar 2018 Posts: 6 Location: Metropolis Zone	Posted: Thu Mar 08, 2018 12:27 am
	Thank you for your reply; I really appreciate it! Since I'm ill I haven't been able to work on it yet. As soon as I made some progress, I will let you know! ;)

Strahssis Joined: 05 Mar 2018 Posts: 6 Location: Metropolis Zone	Posted: Sat Mar 17, 2018 12:55 am
	asynchronous wrote Quote Wouldn't it be less time consuming to just reflow everything rather then looking over all the traces? Sure, if you're keen to solder some more then go for it! If the problem is a dry joint then you'll fix it. If the problem is not a dry joint and a faulty track then the soldering won't do jack. Quote Besides, if a trace is broken, there shouldn't be continuity to the ICs, but there is, so that wouldn't really make sense to me, right? Intermittent faults like what you're seeing can be difficult to find and can be subject to factors like temperature. That's where the chopstick and can of cold spray come in in narrowing down the fault. You're on the right track though. Check the supply and ground. Check the signals. Reflow the joints. Check the resistors. Then contemplate next steps if none of that works. Without the console in front of me I can only help so much. Today I spent half a day reflowing every single connection on the board. At first with some very nice succes; I was able to play games for at least 15 minutes; then I turned off the console to reassemble it again, and guess what; it didn't work anymore. However, it did work again a bit earlier this evening, but a few minutes ago it didn't work again. It appears to be completely random; the console only seems to work when it feels like doing so. The symptoms are still pretty much the same; the game either controls itself; the controls are unresponsive or the controls are wrong; like when I press right, it jumps instead. Also interesting to point out is that only my Master System controller works; my Atari joypad, Genesis controller and the original SJ-152 don't work at all; with different symptoms. Reflowing the connections I noticed that a few pins of multiple IC's had quiet a bit of rust on them. I did get continuity through them however and of course I cleaned them up for as much as possible. Do you still think it could be a broken trace? Wouldn't a bad IC really not be an option? Maybe not the Z80, but those two connected to the controller ports. I'm far from an expert on this, but I have never seen bad or broken connections causing glitches like this; with bad connections it either works or doesn't, but not much in between; correct me if I'm wrong. Please let me know what you think is the next step; I will be working on it next week then!

TmEE Joined: 31 Oct 2007 Posts: 853 Location: Estonia, Rapla city	Posted: Sat Mar 17, 2018 7:51 am
	You wouli want to run wires from the points of controller connectors to wherever the tracks end up, the machine uses a crappy single sided PCB and the ports are not going to be able to handle much mechanical stress at all. With wires the stress disappears into the wire and all the mechanical issues disappear.

asynchronous Joined: 14 Aug 2000 Posts: 742 Location: Adelaide, Australia	Repair -> SG1000-II faulty control unit! Posted: Mon Mar 19, 2018 2:38 pm
	It's possible it could be the logic IC's responsible for the controller ports. No harm in replacing those. These are the smaller chips approximately 1 cm x 2 cm; 74LS32, 74LS139, 74LS257 (there's 2 of these). While you're at it replace the twelve 4.7k resistors as well. But those symptoms you describe totally sound like track or solder faults, where it works fine and then intermittently stops working due to mechanical stress or temperature change etc. As I said these sort of faults can be hard to isolate and fix, even for people who have experience in electronics. That's what you're up against. You've got nothing to lose in trying to repair.

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