National FS-VG501, repair and usage problems

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By mars2000you

Enlighted (5823)

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13-03-2021, 12:13

672kB if I good understand?

By popolon_

Master (152)

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13-03-2021, 12:35

Yes, that is total amount.

By gdx

Enlighted (4192)

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13-03-2021, 13:47

I think some RAM chips are out of order.

By popolon_

Master (152)

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13-03-2021, 13:55

Very many to remove and test...maybe then sram could be put instead.

By gdx

Enlighted (4192)

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13-03-2021, 15:10

I think you can start to put sockets and buy two or four RAMs to find how much are out of order. (4464)
I don't think it's the 4164 that cause this problem.

By popolon_

Master (152)

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13-03-2021, 15:12

I think i start with :
4x4464-15 = 128KB
4x4164-15 = 32KB
as these must be at least somehow combined, because there is only 4x 4164, and not x8. And these are at same pcb area. those other 16x 4464 are in straight row.

By popolon_

Master (152)

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21-03-2021, 13:12

I tried just to put working dram chip over the original dram chip in PCB, but there was no visible difference (i went through all the DRAMS in this way).
I also took termal camera picture, and it seems 3 A/D chips are running about 45-50 celsius, and one logic chip at 50. DRAMs are at 30.
ir_cam_vg501.jpg

By popolon_

Master (152)

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23-03-2021, 21:20

I draw the fs_cv501 cartridge side schematics into kicad:
cv501_cart.png

It can be found from:
https://github.com/popolonx/MSX_STUFF/blob/main/FS-VG501/FS_...

It seems the logic is:
4000H->7FBFH
rom enabled, switch (74LS245) disabled

7FC0H -> 7FFFH
rom disabled, switch (74LS245) enabled, read/write data to digitizer:
P1 in/out buffered D0
P2 in/out buffered D1
P3 in/out buffered D2
P4 in/out buffered D3
P5 in/out buffered D4
P6 in/out buffered D5
P7 in/out buffered D6
P8 in/out buffered D7
P9 output= L
P10 output = buffered _WR
P11 output = buffered _RD
P12 output = buffered A0
P13 output = buffered A1
P14 output = H
P15 = GND
P16 = GND

8000H->BFBFH
rom enabled, switch (74LS245) disabled

BFC0H -> BFFFH
rom disabled, switch (74LS245) enabled, read/write data to digitizer:
P1 in/out buffered D0
P2 in/out buffered D1
P3 in/out buffered D2
P4 in/out buffered D3
P5 in/out buffered D4
P6 in/out buffered D5
P7 in/out buffered D6
P8 in/out buffered D7
P9 output= H
P10 output = buffered _WR
P11 output = buffered _RD
P12 output = buffered A0
P13 output = buffered A1
P14 output = L
P15 = GND
P16 = GND

By popolon_

Master (152)

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05-04-2021, 22:16

Something broke after I pushed the pcb down when using scope, then 13 ram chips (4464) from bottom row went to 70 celsius (from the original 30 celsius). When I took those out, those were identified as faulty by retro chip tester. I will replace those, but it is not certain if the pcb is otherwise working anymore(those gate array chips for example).
Anyway I wrote schematics to kicad, there are still some connections missing:
https://github.com/popolonx/MSX_STUFF/blob/main/FS-VG501/Fra...

There is bytes stored to two registers when _WR and address is:
BFC0H -> write byte to register 1 ( bits 1Q0...7 in schematics)
BFC1H -> write byte to register 2 ( bits 2Q0...7 in schematics)
These bits are used when analog signal is build from digital. But the logic is very complex.

There is 3x 6 bit AD chips, but i am not sure if these are then digitizing R,G,B signals. There is also 3x output AD conversion (6 bit) in this pcb.

By popolon_

Master (152)

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08-04-2021, 22:54

I think now the pcb is quite ready. Only analog video part from this pcb is missing (and the separate analog pcb also).
https://github.com/popolonx/MSX_STUFF/blob/main/FS-VG501/Fra...

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