Large problem, MSX computer not displaying anything

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Por Eugeny_Brychkov

Paragon (1232)

imagem de Eugeny_Brychkov

12-10-2009, 22:14

Initial flickering occurs when voltage is applied to the system, and it hopefully means that VDP's output circuits are ok.

You will not solve problem without special troubleshooting tools: multimeter, logic probe or oscilloscope.
Get a tool like this http://www.electronixexpress.com/test/dp-21.jpg

8250 is the one using V9938 and S3527 MSX engine.

As you checked that power is ok, start using logic probe to see activity on specific pins. On each of the pins below you should see activity:

(0) Ensure you connected everything correctly (e.g. analog unit to the main board);

(1) General functionality
1a. CPU, pin 26 (/RESET). You should ensure that when you power up, it is low, and then switches to steady high;
1b. VDP, pin 8 (CPUCLK). If there's no separate clocking logic, this signal is used as clock for whole the system;
1c. CPU, pin 24 (/WAIT). Clocking here means that MSX cycling (M1) works ok;
1d. CPU, pin 16 (/INT). Seeing clocks here we will ensure that VDP generates required interrupts (INT38h in Mode1);

(2) Vital system lines of the CPU
2a. Address lines on the CPU: pins 1-5, 30-40;
2b. Data lines: 7-10, 12-15;
2c. Control lines: 19-22, 27, 28.

(3) Memory and BIOS
3a. IC119, pins 22 and 20. This is a BIOS chip, and should be accessed heavily when you turn on the machine;
3b. IC134, pins 4 and 5 (/WE and /RAS). Row strobe (r/w+refresh);
3c. IC133-IC136, pin 16 (/CAS). Column select (r/w);
3d. IC146, pin 1 (MUX). Address multiplex to the memory;

(4) VDP operation
4a. pins 25, 30, 31. VDP interface with the CPU;
4b. IC102, pins 4 and 5 (/RAS and /WE);
4c. IC102 and IC104 pin 16 (/CAS);
4d. VDP memory data lines: pins 41-48;

Well, checking the list above should be enough to troubleshoot why MSX does not come up on SCART.

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