Panasonic 2+ A1WX: problems enabling Z80 Turbo mode

By amazin

Supporter (5)

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22-09-2021, 11:54

Guys (and gals) first post here.

I have a friend's Panasonic MSX 2+ FS-A1WX, that had a failed 512K upgrade, he sent it for repais, the technician reverted it back to 256K as it's much less aggressive (as it was planned from factory). Computer was very unstable afterwards, so he sent it to me to have a look, and I found out that all the pads/vias near the memory area had ripped pads from the motherboard. I soldered wires connecting the socket legs/pins to each other directly and it fixed the issue, very stable now, runs everything, passes all tests.

But we started to notice that, since it's very easy to enable the Z80 Turbo mode using the "T" key on the Carnivore 2 menu, the computer would crash like 1/3 of the time. Using the turbo.com MSXDOS utility crashes it as well.

What would you do to start checking for problems on this situation, on this computer? I'm not a hardware expert, far from it, just trying to make my friend's computer more reliable.

Note: when it doesn't crash straight away after enabling the Turbo mode, the computer works great. If you don't enable the turbo, it works perfectly. If you try to enable it, and it doesn't crash/hang immediately, it will also work in turbo mode all the time, perfectly, runs games.

Any idea what could be causing that, where to look for issues?

Thanks in advance

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By st1mpy

Paladin (825)

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22-09-2021, 11:59

Speed rating of the ram memory chips used?

By Guillian

Prophet (3450)

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22-09-2021, 12:09

Have you tried to enable the turbo mode without the Carnivore 2?
According to Carnivore 2 documentation: the correct operation of the Carnivore2 cartridge is not guaranteed in the R800 mode on Panasonic Turbo-R computers.
So perhaps the turbo mode is causing problems.

By Grauw

Ascended (10056)

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22-09-2021, 12:39

I would say speed rating, and also avoid mixing chips of different types...

By amazin

Supporter (5)

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22-09-2021, 13:37

Hi all, thanks for the prompt responses.

I've used 2x Toshiba TC514256AP-70 memories. In fact I bought several of them, and I've performed the same upgrade on my own Panasonic A1WX, with absolutely no issues.

This is the data sheet for it:
https://datasheetspdf.com/pdf-file/1347642/Toshiba/TC514256A...

@guillian: yeah I also have a Turbo R, and the turbo mode works perfectly there as well. But this Panasonic FS-A1WX is a MSX2+ class machine, not a Turbo-R

Thanks!

By amazin

Supporter (5)

amazin's picture

22-09-2021, 13:40

Oh, by the way, the Turbo issue happened to this computer even before I replaced the memories!

It happened when it had 512K of RAM, then it continued happening when the technician downgraded it back to 256K, and still persists after I redid the work and replaced the sockets and memories with the ones I have.

Thanks!

By Grauw

Ascended (10056)

Grauw's picture

22-09-2021, 13:43

If you swap them with the chips in your A1WX, do the problems go away?

Perhaps the chips are fake, relabeled chips of another type with a lower speed rating? Where did you get them from, and do you see indications of relabeling? E.g. does it show clear sanding markings, or does the printing on the chips reflect under different light angles, or if you rub acetone on the top does black stuff come off?

By amazin

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22-09-2021, 13:47

I don't think the issue is related to my memories, as it happened before with other memories, when it had 512K and then with the memories supplied by the technician that tried to fix it before.

But yeah I can try swapping with others and to the ones on my MSX

The memories look absolutely new, I tried the acetone method when they got here, they are originals.

But it appears that it's something else, perhaps on the circuit that does the change from standard to turbo speed. Because when it works, it runs in Turbo mode all day if you don't turn it off. Absolutely no problems whatsoever.

By st1mpy

Paladin (825)

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22-09-2021, 13:53

Does it crash even when you don't have any cartridges inserted? Or only when something like a C2 is inserted?

I wrote a reply to some different thread once cos I had something not working only on my WX. But It did work when I insert a cartridge in a slot expander. If you own a slot expander, try inserting the C2 through it. What I thought was happening is, the main slot is noisy and the expander buffers signals so its better. (It's probably related to the power circuit in the WX aging).

By amazin

Supporter (5)

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22-09-2021, 14:56

@st1mpy: I haven't tried without the C2 cartridge connected, because then it'll boot straight into non-Turbo mode, and it will work absolutely fine.

But I'll try to copy the turbo.com utility to a floppy and boot off it.

Thanks!

By Meits

Scribe (6446)

Meits's picture

22-09-2021, 15:08

You can switch modes in basic:
turbo on: OUT 64,8: OUT 65,0
turbo off: OUT 64,8: OUT 65,1