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Need Help with repair of a Sega Master System 1 VA3
Posted: Wed Apr 13, 2022 9:22 pm
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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 |
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Posted: Sat Apr 16, 2022 6:33 am |
No one here that can help me? | |
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Posted: Sat Apr 16, 2022 9:48 am |
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... |
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Posted: Sat Apr 16, 2022 11:05 am |
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.
I would confirm the console works as a PAL system first. |
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Need Help with repair of a Sega Master System 1 VA3
Posted: Sat Apr 16, 2022 1:31 pm
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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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