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Hello.
I have received as a "gift" a "dead" TecToy Master System 1 PCB and was trying to fix it.
So far so good everything was going fine, I was harvesting many parts from the junk pile and putting them in the place of the missing ones.
After finally being able to turn it on, I discovered that the BIOS chip was busted, getting very hot very quickly. I socketed it so I could try other options.

The last thing that was missing was the crystal.
The original is 10.726834 Mhz, the one I got is 10.1378 Mhz.
As expected, the console booted, but the video was black and white and with some jumping lines and weird random colors around.

I've got a proper frequency crystal, a weird thing happened.
The console simply shows a black screen with some faint vertical lines when I use the crystal that has the proper frequency but boots fine with the color problem with the other one.

I just don't know what to look for next, can someone please give me some ideas?

WhatsApp Image 2022-01-13 at 07.36.22.jpeg (192.86 KB)

Before

20220116_190154 (2).jpg (1.28 MB)

After

I found it!
I've read that a black screen has big chances of being caused by either the Z80 or his RAM.
I first socketed the RAM and tried a 6264 I had lying around with no results, but after I changed the Z80 everything did come back to normal, I guess it's somewhat damaged.

What could have fried the BIOS and damaged the Z80 is a mistery to me... maybe a lighting or some kind of power surge?

Anyway thanks to anyone that at least have read this, hope this small information can help someone else in the future.

Someone using an incorrect power adapter at some point is maybe a potential cause?

Probably.
But it was missing the transistor and the regulator, as can be seem on the pictures.
The zener diode was fine.

In case someone is curious, I've got some pictures and even a small video here: https://drive.google.com/folderview?id=1DJzcpGi4BIG6iMuHq8F8mJTyh2EuBA9E

Author	Message
Fisher Joined: 10 May 2015 Posts: 23	[SOLVED] Another weird Master System black screen Posted: Thu Jan 20, 2022 1:16 pm Last edited by Fisher on Sat Jan 22, 2022 7:43 pm; edited 2 times in total
Fisher Joined: 10 May 2015 Posts: 23	Hello. I have received as a "gift" a "dead" TecToy Master System 1 PCB and was trying to fix it. So far so good everything was going fine, I was harvesting many parts from the junk pile and putting them in the place of the missing ones. After finally being able to turn it on, I discovered that the BIOS chip was busted, getting very hot very quickly. I socketed it so I could try other options. The last thing that was missing was the crystal. The original is 10.726834 Mhz, the one I got is 10.1378 Mhz. As expected, the console booted, but the video was black and white and with some jumping lines and weird random colors around. I've got a proper frequency crystal, a weird thing happened. The console simply shows a black screen with some faint vertical lines when I use the crystal that has the proper frequency but boots fine with the color problem with the other one. I just don't know what to look for next, can someone please give me some ideas? WhatsApp Image 2022-01-13 at 07.36.22.jpeg (192.86 KB) Before 20220116_190154 (2).jpg (1.28 MB) After

Fisher Joined: 10 May 2015 Posts: 23	Posted: Sat Jan 22, 2022 7:41 pm
Fisher Joined: 10 May 2015 Posts: 23	I found it! I've read that a black screen has big chances of being caused by either the Z80 or his RAM. I first socketed the RAM and tried a 6264 I had lying around with no results, but after I changed the Z80 everything did come back to normal, I guess it's somewhat damaged. What could have fried the BIOS and damaged the Z80 is a mistery to me... maybe a lighting or some kind of power surge? Anyway thanks to anyone that at least have read this, hope this small information can help someone else in the future.

KingMike Joined: 14 Oct 2008 Posts: 533	Posted: Sun Jan 23, 2022 5:02 am
KingMike Joined: 14 Oct 2008 Posts: 533	Someone using an incorrect power adapter at some point is maybe a potential cause?

Fisher Joined: 10 May 2015 Posts: 23	Posted: Sun Jan 23, 2022 1:48 pm
Fisher Joined: 10 May 2015 Posts: 23	Probably. But it was missing the transistor and the regulator, as can be seem on the pictures. The zener diode was fine. In case someone is curious, I've got some pictures and even a small video here: https://drive.google.com/folderview?id=1DJzcpGi4BIG6iMuHq8F8mJTyh2EuBA9E

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View topic - [SOLVED] Another weird Master System black screen