Wavy23 won't boot up

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By FozzTexx

Supporter (8)

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20-06-2017, 04:48

No, I didn't really expect that putting in a game cartridge would change anything, but it was an easy thing to do and I've seen in some other threads that it's something that is often asked to try. And you'd be surprised how often piggybacking a chip actually works to get things going. It seems stupid since the lines should be stuck, but often they just aren't being driven and the piggybacked chip is able to control the line. It was another easy thing to test and I have had success with the technique with both RAM and 74 series chips.

Poked around some more with the logic probe. The /INT line on the Z80 is stuck high, same on the V9938. There's activity on the address and data lines on all six RAM chips, however /G is stuck high on the two for the Z80, and stuck low on the four for the VDP.

By Wlcracks

Champion (467)

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20-06-2017, 08:04

I had the same diagnose on a MSX, finally it was the mask ROM. In your case still could be the RAM or VDP. The ROM has to set the VDP in interrupt mode I guess. Does the board contain a logic array or MSX engine? Is there any activity on the "analog" video outputs on the VDP? Socketing ROM, RAM and suspicious logic chips is still easiest and cheapest way to diagnose I guess, when not having any schematics.
I couldn't find any pictures of the board, you mind sharing that with us?

Not sure what you mean with /G

By FozzTexx

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20-06-2017, 16:53

According to the datasheet /G is essentially the enable pin. The Wavy23 is this one, mine is the gray model.

The chips are all pretty basic: Z80, V9938, TMS4464, 74LS157, 74LS14, 74LS32, 74LS30, 74LS145, 74LS22, 74HC04, MC1377P, and the two mask roms HN613256P & HN613128P.

Guess I'll see if I can find a copy of the ROMs somewhere.

By Wlcracks

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20-06-2017, 20:21

mail sent

By FozzTexx

Supporter (8)

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21-06-2017, 00:57

What do you mean "mail sent"?

By Wlcracks

Champion (467)

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21-06-2017, 19:37

I have sent you an email? With the info you need about the roms.

By FozzTexx

Supporter (8)

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22-06-2017, 04:07

MSX.org's outgoing email is broken. I never got an email, and after I figured out what you had tried to do I tried sending you one which it appears you never got either. I did find a copy of the ROMs on some web site. I'll have to desolder the ROMs from the Wavy23 so I can compare them. I'm not convinced the ROMs are bad yet though. If one of the 74xx chips are used to enable the ROMs it might be that, seems like it's always 74xx chips that go bad. But I don't have a schematic so I'm not sure which one(s) might control the ROMs.

By Wlcracks

Champion (467)

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22-06-2017, 07:09

cool

By l_oliveira

Hero (533)

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25-06-2017, 20:17

Z80 is a physically weak, fragile chip which breaks down way too often. That's why a lot of MSX computers have the Z80 chip separated from the rest of the computer using buffer ICs. I don't think the SANYOs do have buffers, though. Which could be why yours broke.

I suggest you pop the Z80 out and try it on a known working system which uses a Z80 (Coleco, other MSX, Master system, etc). It's easier for you to have a bad Z80 than bad ROMs but either are a possibility. If you had bad RAM you would have some bus activity.

Have you checked the M1 pin on the Z80? Is that pulsing?

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