Wavy23 won't boot up

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By FozzTexx

Supporter (8)

FozzTexx's picture

18-06-2017, 19:33

I recently got a couple of Wavy23 systems off eBay in a late night impulse buy. One works and one doesn't. The one that doesn't powers up but only gives me black video. Pushing caps lock doesn't cause the light to change. I've been unable to find any schematics, but from reading the forums it looks like you guys are very much experts on repairing all kinds of different MSX systems.

What I've done so far:

  • Checked the voltages: +5V, +12V, and -12V all read ok.
  • Used logic probe to check that the Z80 is getting clock and it is
  • Tried piggybacking the six 4464 chips with known good ones, no effect
  • Used the logic probe to check that there is activity on the data & address lines
  • Tried the Arkanoid and Xevious cartridges I have but still black video

When it first turns on the Z80 pulls /HALT low and /RESET is high. If I let it warm up for a bit and hit reset /HALT goes high and stays high, but it still doesn't boot up. My guess is that the Z80 isn't finding the ROMs to start the boot code.

Tools I have available: multimeter, logic probe, Saleae Logic 16, and a very old purely analog Tektronix 2 channel oscilloscope. I do have some experience with repairing old computers and arcade machines. I also have some of Marcelo Zoffy's EPROM boards and can burn ROMs if there's a diagnostic program that will fit I should try.

Any assistance you can give would be greatly appreciated!

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By hamlet

Paladin (856)

hamlet's picture

18-06-2017, 21:19

I´m not much of a hardware crack, just want to welcome you! But I´m sure other members will help.
Did you have a game cartridge or a memory expansion cartridge to test with?

By Manuel

Ascended (13421)

Manuel's picture

18-06-2017, 22:32

hamlet: he said he already tried Arkanoid and Xevious cartridges. Fozztex: is it correct you didn't get any sound when you ran these games?

Are the ROMs socketed?

By hamlet

Paladin (856)

hamlet's picture

18-06-2017, 22:49

Yes, I should'nt read, cook and write at once. But food was ok.

By FozzTexx

Supporter (8)

FozzTexx's picture

18-06-2017, 23:37

Correct, there is no sound when trying a cartridge.

The ROMs on the Arkanoid and Xevious are not socketed but I have some EPROM cartridges that are. They only take 27c512s though so 64k is the max ROM size I can put on them, though I haven't tried anything besides 16k and 32k ROMs.

By Meits

Scribe (4474)

Meits's picture

19-06-2017, 00:02

I guess Manuel's question about socketed ROMs was more about the ones in your Sanyo.
You could try to create fresh system ROMs and put them in these sockets if they're there.

By FozzTexx

Supporter (8)

FozzTexx's picture

19-06-2017, 02:27

No the ROMs in the Sanyo are not socketed, they are soldered in mask ROMs.

By sd_snatcher

Prophet (2573)

sd_snatcher's picture

19-06-2017, 03:21

Do you have an external memory cartridge (i.e.: Memory Mapper)? If so, plug it an see if the machine boots.

By FozzTexx

Supporter (8)

FozzTexx's picture

19-06-2017, 03:28

No I don't have an external RAM or Memory Mapper cartridge.

By Wlcracks

Expert (122)

Wlcracks's picture

19-06-2017, 17:40

Is the videochip generating interrupts to the z80?. Best check at z80, could have some logic ports between z80 and vdp. Then trace it back to the VDP. If not -> ROM or video chip?

Piggybacking ram is only possible when logic probe shows toggling on each RAM chip lines. I am not sure this is a good test to do. Best to socket them. If the RAM keeps the lines high or low, you stil get the same "picture".

Not sure why trying a game in ROM should work, when its using bios or ram.

By Wlcracks

Expert (122)

Wlcracks's picture

19-06-2017, 17:48

Syntax Error

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