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Hello everybody :)

i have a Sega Master System 1 Powerbase with a Board Revision VA3.

My problem is, that it seems that the oscillator is dead. It is a PAL-Version and i can't find any replacement. So i decided to change the PAL against a NTSC oscillator.

I read any post i could find in this forum about how to convert a pal sms into a ntsc one. I found many interesting things but nothing about the PCB Model VA3 :(

What i found was the following:

1.) change the pal oscillator to a ntsc one
2.) lift up pin 57 from VDP (IC5) and connect it with GND
3.) lift up pin 7 from CXA1145P and connect it with pin 12 (5V)
4.) remove resistor between IC4 and CXA1145P
5.) connect pin 6 from CXA1145P with a 3.3k resistor and then with pin 6 (CLK) from Z80

My problem is point 4.

In the service manual IC4 is with a 3.3k Resistor (R20) connected to CXA1145P. The VA3 doesn't have a resistor R20. Can anybody please tell me if my list above is correct and which resistor i have to remove?

best regards from germany,
Patrik

No one here that can help me?

Trigger58 wrote

Hello everybody :)
4.) remove resistor between IC4 and CXA1145P

Do you mean IC14 rather than IC4? R20 in the service manual is between these two devices.

Not being able to readily find a VA3 schematic, I'm very much speculating here, but assuming there really isn't a 3k3 resistor between IC9 and IC14, I'd say you want to cut the track instead. My guess is that the instruction to remove the resistor is just an easy way to sever the path between IC9 and IC14.

The point of the mod appears to be to use the system clock (~3.54MHz) to drive the chrominance sub-carrier for IC9, rather than the output from the clock divider at IC14 which is labelled 4.73...MHz on the schematics.

I'm assuming the system clock is derived from the ~10.64MHz clock at the top of the schematic, via a further divide by 3 inside the VDP module.

So, I'd say are you sure there is no resistor between IC9 and IC14 (and are you sure you're looking at IC14 and not IC4 as you say!?); and if there definitely isn't I'd think about cutting the track somewhere.

What is connected to pin 6 of IC9 as it happens? If you still have the equivalent of R21 on the VA1 schematic (it's a 1k resistor between C50 and ground), that could be a convenient point to solder the mod wire to for the system clock.

Photos might help...

Trigger58 wrote

Hello everybody :)

i have a Sega Master System 1 Powerbase with a Board Revision VA3.

My problem is, that it seems that the oscillator is dead. It is a PAL-Version and i can't find any replacement.

Hello,

How did you come to the conclusion the oscillator was dead?
As to replacements, at least the 10.738635 MHz and 53.203424 MHz ones are easy to find.I don't know what is the value installed in a PAL VA3, could be something else.

Trigger58 wrote

So i decided to change the PAL against a NTSC oscillator.

I would confirm the console works as a PAL system first.

Can you share what tests you performed to conclude that the XTAL was dead?

This post, where a conversion from PAL to NTSC was successfully done on a Master System 2, may be helpful: https://www.smspower.org/forums/18175-PALSMSIIInTheUS

Author	Message
Trigger58 Joined: 13 Apr 2022 Posts: 2	Need Help with repair of a Sega Master System 1 VA3 Posted: Wed Apr 13, 2022 9:22 pm
Trigger58 Joined: 13 Apr 2022 Posts: 2	Hello everybody :) i have a Sega Master System 1 Powerbase with a Board Revision VA3. My problem is, that it seems that the oscillator is dead. It is a PAL-Version and i can't find any replacement. So i decided to change the PAL against a NTSC oscillator. I read any post i could find in this forum about how to convert a pal sms into a ntsc one. I found many interesting things but nothing about the PCB Model VA3 :( What i found was the following: 1.) change the pal oscillator to a ntsc one 2.) lift up pin 57 from VDP (IC5) and connect it with GND 3.) lift up pin 7 from CXA1145P and connect it with pin 12 (5V) 4.) remove resistor between IC4 and CXA1145P 5.) connect pin 6 from CXA1145P with a 3.3k resistor and then with pin 6 (CLK) from Z80 My problem is point 4. In the service manual IC4 is with a 3.3k Resistor (R20) connected to CXA1145P. The VA3 doesn't have a resistor R20. Can anybody please tell me if my list above is correct and which resistor i have to remove? best regards from germany, Patrik

Trigger58 Joined: 13 Apr 2022 Posts: 2	Posted: Sat Apr 16, 2022 6:33 am
Trigger58 Joined: 13 Apr 2022 Posts: 2	No one here that can help me?

willbritton Joined: 06 Mar 2022 Posts: 670 Location: London, UK	Posted: Sat Apr 16, 2022 9:48 am
	Trigger58 wrote Hello everybody :) 4.) remove resistor between IC4 and CXA1145P Do you mean IC14 rather than IC4? R20 in the service manual is between these two devices. Not being able to readily find a VA3 schematic, I'm very much speculating here, but assuming there really isn't a 3k3 resistor between IC9 and IC14, I'd say you want to cut the track instead. My guess is that the instruction to remove the resistor is just an easy way to sever the path between IC9 and IC14. The point of the mod appears to be to use the system clock (~3.54MHz) to drive the chrominance sub-carrier for IC9, rather than the output from the clock divider at IC14 which is labelled 4.73...MHz on the schematics. I'm assuming the system clock is derived from the ~10.64MHz clock at the top of the schematic, via a further divide by 3 inside the VDP module. So, I'd say are you sure there is no resistor between IC9 and IC14 (and are you sure you're looking at IC14 and not IC4 as you say!?); and if there definitely isn't I'd think about cutting the track somewhere. What is connected to pin 6 of IC9 as it happens? If you still have the equivalent of R21 on the VA1 schematic (it's a 1k resistor between C50 and ground), that could be a convenient point to solder the mod wire to for the system clock. Photos might help...

Apocalypse Joined: 26 Feb 2021 Posts: 159	Posted: Sat Apr 16, 2022 11:05 am
Apocalypse Joined: 26 Feb 2021 Posts: 159	Trigger58 wrote Hello everybody :) i have a Sega Master System 1 Powerbase with a Board Revision VA3. My problem is, that it seems that the oscillator is dead. It is a PAL-Version and i can't find any replacement. Hello, How did you come to the conclusion the oscillator was dead? As to replacements, at least the 10.738635 MHz and 53.203424 MHz ones are easy to find.I don't know what is the value installed in a PAL VA3, could be something else. Trigger58 wrote So i decided to change the PAL against a NTSC oscillator. I would confirm the console works as a PAL system first.

asynchronous Joined: 14 Aug 2000 Posts: 742 Location: Adelaide, Australia	Need Help with repair of a Sega Master System 1 VA3 Posted: Sat Apr 16, 2022 1:31 pm
	Can you share what tests you performed to conclude that the XTAL was dead? This post, where a conversion from PAL to NTSC was successfully done on a Master System 2, may be helpful: https://www.smspower.org/forums/18175-PALSMSIIInTheUS

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