CX5MII/128 converision

Hero (538)

29-04-2016, 23:27

Hi all, I just got a CX5MII/128A (Australia) and it comes with the CX7 board. I've already talked to Alexey Podrezov to get his expansion boards as I follow the other posts about the CX5MII conversion.

My question is about the sub-ROM address MOD (I suppose I have to change it's address from $4000 to $0000) and about the RTC. How to install a RTC and make it a full MSX2 compliant. Does anyone here have a full resolution picture of the CX7 board populated with MSX2 components ?

All the other mods I get on internet are on XB300 board (the previous model). Since this one seems to be the same board used on CX7 and YIS604 I presume the address mapping is a question of jumpers.

Thxs

Por Grauw

Ascended (10577)

30-04-2016, 00:45

RTC schematics for the CX7 board can be found in the YIS503IIIR service manual iirc.

Por retrocanada76

Hero (538)

30-04-2016, 01:08

The service manual I found (russian site with separate pages scanned) does not have a bill of materials. It's hard to know for example what is the value for the Q302 for example.

Por caro

Champion (512)

30-04-2016, 04:19

retrocanada76 wrote:

The service manual I found (russian site with separate pages scanned) does not have a bill of materials. It's hard to know for example what is the value for the Q302 for example.

Q301,303~306 : 2SA933S
Q302,307~310 : 2SC1740S

Por retrocanada76

Hero (538)

30-04-2016, 19:56

Thxs,

but I still need more info as the IC311, IC315, IC320, IC316, IC313 ?
Also C319 shows 10/16 ? 10uF 16V ?
D301 which diode here ?

Thxs again

Por maxis

Champion (512)

30-04-2016, 20:37

@Retrocanada76

I've populated a while ago the same board. It does work well:

https://flic.kr/p/GCvUNH
Zoom the picture, you will see all the resistor values and chip marking. I used HC instead of LS series.

Discard the white wires. These are for the MSX2+ ROM bank select.

Por retrocanada76

Hero (538)

30-04-2016, 20:43

cool what is the diode d301 and d302?

Do you have any part list ?

Por maxis

Champion (512)

01-05-2016, 01:56

retrocanada76 wrote:

cool what is the diode d301 and d302?

Do you have any part list ?

d301 - 1n4148 (subsitute for the small signal rectifier)
d302 - Correction: I've checked again - 1n5229b I've ordered in the past.

From what I remember, all the resistors and caps are like in the original schematics.

Por retrocanada76

Hero (538)

01-05-2016, 01:09

Maxis,

Is there any other jumper to change to turn it into a MSX2 ? Besides the VRAM + ROMs ? I know the subrom starts at $4000 according to schematics, but is it mirrored to $0000 on this board ?

Por maxis

Champion (512)

01-05-2016, 02:27

retrocanada76 wrote:

Is there any other jumper to change to turn it into a MSX2 ? Besides the VRAM + ROMs ? I know the subrom starts at $4000 according to schematics, but is it mirrored to $0000 on this board ?

Well, Yamaha was cutting the traces on that particular motherboard for almost every model flavor. I do have the mobo from YIS503II/R. So in my case the SUBROM position wasn't populated at all.

However, in your case pin22 (#OE) of SUBROM quite likely was re-routed (CX5MII), but the original unmodified schematics is actually MSX2. So,
- Disconnect CS1 going to the #OE of SUBROM.
- Restore the trace coming from pin 12 of IC307 (74LS10) to the #OE of SUBROM.

Happy hacking

Por retrocanada76

Hero (538)

01-05-2016, 03:06

Great, I think I have the part list (for my board at least):

IC308 RP5C01
IC313 74HC175
IC316 74LS32
IC320 74HC30

CR322 CRYSTAL 32.7680 KHZ
TC301 TRIMMER 12-60PF

C313 CERAMIC 68PF
C319 ELKO 10UF 16V

Q301 2SA933S
Q302 2SC1740
Q303 2SA933S

RA302 RES ARR. 8 X 100K OHM
R301 680 OHM
R302 22K OHM
R303 30K OHM
R304 1.2K OHM
R305 6.8K OHM
R306 4.7K OHM
R307 330 OHM
R308 100K OHM
R309 47K OHM
R310 100K OHM

D301 1N4148
D302 1N5229B

I'll order those items and try out. Thxs.