Problem NMS-8245 2+, black screen

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Por Caliostro

Expert (80)

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10-06-2021, 16:02

Hi all, after solving with your help the transformation of a NMS-8220 2+, I went back to the problems of a NMS-8245, I bought this broken MSX, already transformed into 2+, I replaced cpu, vdp, ram , vram, rom and all electrolytic capacitors, the machine turns on with green leds power and caps, caps and relays shake for 2 seconds, the screen stays black and strange sounds are heard, pressing the reset button, the sounds change, I tried to remove the TMS2793 chip and the sounds don't change

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Por Caliostro

Expert (80)

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11-06-2021, 13:01

the clock signal is present, but unfortunately I have a logic probe, I don't have an oscilloscope

Por Jipe

Paragon (1504)

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11-06-2021, 13:27

you must first test all the tracks of the circuit that have been desoldered to replace the components for transformed in 2+
some pellets with metallic holes can come out by desoldering
have you sockets on cpu vdp ram and rom ?

Por Caliostro

Expert (80)

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11-06-2021, 13:42

yes i tested all tracks of CPU, VDP and ROM, now i try RAM and VRAM, but i have little hope

Por Caliostro

Expert (80)

Imagen del Caliostro

11-06-2021, 14:51

I found a broken track (RAM), fixed and now I turn on, no relay noise, no sound and power led and caps on

Por Jipe

Paragon (1504)

Imagen del Jipe

11-06-2021, 15:19

if is easy to remove the VDP check with a V9938 and original ROM

Por Caliostro

Expert (80)

Imagen del Caliostro

11-06-2021, 15:46

unfortunately I don't have a 9938 available

Por Caliostro

Expert (80)

Imagen del Caliostro

11-06-2021, 17:16

is there a rom that starts only basic services?

Por Jipe

Paragon (1504)

Imagen del Jipe

11-06-2021, 17:50

try a MSX1 rom
program a 64k eprom with just first 32k with the msx1 rom
i have tested on a Sony HB500 with problems and work on MSX1 mode

Por Caliostro

Expert (80)

Imagen del Caliostro

11-06-2021, 18:20

i tried 6 bios, nothing new, 60hz pal but black screen ... the strange thing is that there is data transmission on cpu, ram and vdp, but it remains blocked

Por Pentarou

Champion (396)

Imagen del Pentarou

11-06-2021, 18:37

Try the C-Bios, it will work even without functional RAM or a RTC.

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