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I recently picked up a master system 1 cheap knowing it was faulty but I want to attempt to fix it.

The fault is that it switches on as in the green light comes on, you get a pop and flicker on the screen but after that it just sits dead.

Following the test procedures in the service manual:

- I've tested the 7805 and its outputting 4.8odd volts so that should be enough.
- I've traced power to most the ICs and its there ok, just need to finish this tonight as at the time I didn't have the pinout of each chip so wasn't sure of the correct pin.

The next step in the manual is to test the reset circuit and I'm think it might be something like that thats bad as the system just seems to stall as it powers up. This step states to measure the voltage of JR should be 0-3.6v slowly rises.

Can anyone advise as to what JR is?

Unfortunately I don't have a scope so I can't test most of the ICs, unless there is a method of testing them with a multimeter, but fingers crossed its something physical that has failed like a capacitor

I've tested all the ics now and they all have power. I think I found JR as pin 35 of ic4 but not sure as this pin has a constant 5v.

I'm a little bit at a loss now as to what the problem may be. The board seems to be an odd revision as I can't find any pictures of it online. It didn't have an rf shield over the entire board but just a small shield over the crystal and a few close smaller chips.

I'm starting to think the board is fried and not really worth the time to fix as a replacement working unit can be had cheap enough. Any thoughts though before I give up?

I was going to post a picture of the board but the forum rules won't let me. It's an m4 pal board dated 1986.

Are you able to link a picture of the board uploaded onto Imgur?

Did you replace all the capacitors?

http://imgur.com/OwE6M9I

Imgur link to a picture of the board. In this pic the small RF shield is removed. You can see the tabs through which it was soldered to the left of the CPU. Essentially it covered the area within the grounding strip around the crystal and 3 smaller ICs.

I haven't replaced the caps as there is a ton of them on the board. I could maybe try replacing the electroylic caps as there isn't as many of them but there must be 50 ceramic ones.

It's an earlier SMS board going by the reset and pause switches, manufactured in mid to late 1987. It's also been modified with RCA sockets which could maybe be the source of your grief.

I think you have the wrong pin on IC4 for the reset circuit but you're on the right track by measuring the reset pin on the 3 IC's to make sure none of them are being held in reset.

The ceramic caps should be fine as long - as none were damaged when the console was modified with the RCA sockets. I'd hold off on replacing the electrolytic caps before running some more basic tests.

If you haven't already, I would start by inserting a few different game cartridges and seeing if you have a game audio signal on the audio line of the AV socket (the factory socket not the RCA). If you have game audio then the system is running. If not then check the clock signals and reset lines just like the manual suggests. Try a few different cartridges and make sure the cartridge PCB and cartridge slot are clean.

I added the rca sockets as I didn't have the proper av cable to hook it up. I took video and audio off the bottom of the av socket so simple enough and nothing was damaged. I've modded a few consoles like this including my master system 2 and while I'm not a soldering expert I like to think I'm good enough for simple mods like this.

I'll try to pickup a proper cable and try that. Might even try it on the rf just to see but I'm fairly sure it's dead. When first switched on there I a 1.5v signal down the video jack that slowly drops in output. NoIain this is the video signal or not bit something is there.

One thing I never though of actually is giving the cartridge slots a good clean so that'll be my next job. I suspect it won't help but no harm in trying.

After that I'll go back to the ic's and start testing again.

Is there a method to check for the clock signal with a multimeter?

So after a bit more testing....

I checked the voltage at the pins labelled reset on the schematic and pin 26 of IC1 is at 5v, pin 41 of IC4 is at 5v and pin 23 of IC5 is at 0.2v.

Maybe this is the issue?

That could be it. Try measuring the continuity between the pin 23 of IC5 and the reset pins on the other 2 IC's. The 3 pins should all be connected.

Author	Message
unite Joined: 24 Apr 2014 Posts: 6 Location: Northern Ireland	Help with faulty Master System 1 Posted: Fri Sep 23, 2016 12:15 pm
	I recently picked up a master system 1 cheap knowing it was faulty but I want to attempt to fix it. The fault is that it switches on as in the green light comes on, you get a pop and flicker on the screen but after that it just sits dead. Following the test procedures in the service manual: - I've tested the 7805 and its outputting 4.8odd volts so that should be enough. - I've traced power to most the ICs and its there ok, just need to finish this tonight as at the time I didn't have the pinout of each chip so wasn't sure of the correct pin. The next step in the manual is to test the reset circuit and I'm think it might be something like that thats bad as the system just seems to stall as it powers up. This step states to measure the voltage of JR should be 0-3.6v slowly rises. Can anyone advise as to what JR is? Unfortunately I don't have a scope so I can't test most of the ICs, unless there is a method of testing them with a multimeter, but fingers crossed its something physical that has failed like a capacitor

unite Joined: 24 Apr 2014 Posts: 6 Location: Northern Ireland	Posted: Sat Sep 24, 2016 10:32 am
	I've tested all the ics now and they all have power. I think I found JR as pin 35 of ic4 but not sure as this pin has a constant 5v. I'm a little bit at a loss now as to what the problem may be. The board seems to be an odd revision as I can't find any pictures of it online. It didn't have an rf shield over the entire board but just a small shield over the crystal and a few close smaller chips. I'm starting to think the board is fried and not really worth the time to fix as a replacement working unit can be had cheap enough. Any thoughts though before I give up? I was going to post a picture of the board but the forum rules won't let me. It's an m4 pal board dated 1986.

Flygon Joined: 30 Jun 2016 Posts: 196 Location: Melbourne, Australia	Posted: Mon Sep 26, 2016 12:46 am
	Are you able to link a picture of the board uploaded onto Imgur? Did you replace all the capacitors?

unite Joined: 24 Apr 2014 Posts: 6 Location: Northern Ireland	Posted: Mon Sep 26, 2016 12:09 pm
	http://imgur.com/OwE6M9I Imgur link to a picture of the board. In this pic the small RF shield is removed. You can see the tabs through which it was soldered to the left of the CPU. Essentially it covered the area within the grounding strip around the crystal and 3 smaller ICs. I haven't replaced the caps as there is a ton of them on the board. I could maybe try replacing the electroylic caps as there isn't as many of them but there must be 50 ceramic ones.

asynchronous Joined: 14 Aug 2000 Posts: 742 Location: Adelaide, Australia	Help with faulty Master System 1 Posted: Wed Sep 28, 2016 3:36 pm
	It's an earlier SMS board going by the reset and pause switches, manufactured in mid to late 1987. It's also been modified with RCA sockets which could maybe be the source of your grief. I think you have the wrong pin on IC4 for the reset circuit but you're on the right track by measuring the reset pin on the 3 IC's to make sure none of them are being held in reset. The ceramic caps should be fine as long - as none were damaged when the console was modified with the RCA sockets. I'd hold off on replacing the electrolytic caps before running some more basic tests. If you haven't already, I would start by inserting a few different game cartridges and seeing if you have a game audio signal on the audio line of the AV socket (the factory socket not the RCA). If you have game audio then the system is running. If not then check the clock signals and reset lines just like the manual suggests. Try a few different cartridges and make sure the cartridge PCB and cartridge slot are clean.

unite Joined: 24 Apr 2014 Posts: 6 Location: Northern Ireland	Posted: Wed Sep 28, 2016 6:50 pm
	I added the rca sockets as I didn't have the proper av cable to hook it up. I took video and audio off the bottom of the av socket so simple enough and nothing was damaged. I've modded a few consoles like this including my master system 2 and while I'm not a soldering expert I like to think I'm good enough for simple mods like this. I'll try to pickup a proper cable and try that. Might even try it on the rf just to see but I'm fairly sure it's dead. When first switched on there I a 1.5v signal down the video jack that slowly drops in output. NoIain this is the video signal or not bit something is there. One thing I never though of actually is giving the cartridge slots a good clean so that'll be my next job. I suspect it won't help but no harm in trying. After that I'll go back to the ic's and start testing again. Is there a method to check for the clock signal with a multimeter?

unite Joined: 24 Apr 2014 Posts: 6 Location: Northern Ireland	Posted: Wed Sep 28, 2016 8:58 pm
	So after a bit more testing.... I checked the voltage at the pins labelled reset on the schematic and pin 26 of IC1 is at 5v, pin 41 of IC4 is at 5v and pin 23 of IC5 is at 0.2v. Maybe this is the issue?

asynchronous Joined: 14 Aug 2000 Posts: 742 Location: Adelaide, Australia	Help with faulty Master System 1 Posted: Thu Sep 29, 2016 10:34 am
	That could be it. Try measuring the continuity between the pin 23 of IC5 and the reset pins on the other 2 IC's. The 3 pins should all be connected.

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