Neo Zemmix Expected Behaviour

By jimmydeath

Supporter (5)

jimmydeath's picture

27-01-2019, 22:16

Hello.

I have just built myself a Neo from a bare PCB that I have purchased and am now trying to fault find it, assuming that it has a fault instead of finger trouble.

What I am trying to understand is what is expected upon startup without any memory card or cartridge inserted, what I am getting is a white screen on video out and a black screen on VGA out. Should there be any logo or text on boot up, does the system halt on any particular errors e.g faulty RAM. I have tried several version of firmware from the KDL site from V3.1 up to the latest but am getting the same result.

Clearly the FPGA is running to some extent because it is generating the H & V sync signals but is difficult to go forwards from here when I am unsure as to how it is supposed to be behaving.

THanks

Regards

James

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By ducasp

Master (147)

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28-01-2019, 11:11

Have you set-up the DIP switches so it is outputing the signal to your VGA monitor? Check if SW2 is on and SW3 off (regular VGA 31Khz) or both on (scanlines added to VGA 31Khz). Also SW8 should be off as you are not using a SDCARD (but I don't think this should prevent the boot screen anyway).

By Grauw

Ascended (8366)

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28-01-2019, 11:32

On startup without memory card or cartridge it should just boot to Basic like any regular MSX.

By jimmydeath

Supporter (5)

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28-01-2019, 14:19

Hello

Thanks for your responses, yes I have changed SW2 & 3 depending on whether I have a TV or a VGA monitor attached.

Now that I know it should boot into basic without anything plugged into the cartridge slots or SD card I can look deeper.

I haven't tried plugging in a keyboard yet, presumably it would still boot to a basic prompt regardless

THanks

Regards

James

By Grauw

Ascended (8366)

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28-01-2019, 14:22

Yep attached keyboard does not matter.

By ducasp

Master (147)

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30-01-2019, 10:56

Jimmy, did you try to set dip switches 3 and 4 and 5 on (disabling external slots)?

By DamnedAngel

Master (143)

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30-01-2019, 13:21

Hi Jimmy,

Some questions that might give some insights

  • Did you check audio for the boot beep?
  • Did you check the live output of the power supply to be sure it is able to drive the proper voltage during operation?
  • Did you connect more than one video outputs at the same time? My Neo Br doesn't like it.
  • Regardless of the dip switches, did you try printscreen/shift + printscreen? They cycle through different video output modes.
  • Did you install the status LEDs? When you change the dip switches configurations, do the LEDs present different status?
  • Did you try (Shift +) F9, F10 and F11? These change PSG/SCC/OPL output levels, and the LEDs should momentarily show the current level.
  • Did you visually inspect the board for bad soldering or short circuits?
  • Do you have any other Neo around to switch components?
  • Did you try to boot with some game cartridges inserted?

best,

By jimmydeath

Supporter (5)

jimmydeath's picture

07-02-2019, 00:59

Hello again

First off - Thanks for all those responding it has been very helpful.

Anyway I have just had that eureka moment or maybe it should be doh!

So whilst working through the circuit I held the reset button down longer than normal and the NEO logo popped up followed by the MSX basic prompt. It would seem, most likely that whatever switch I have is the reverse of what it should be i.e. NC rather than NO or the opposite way round.(which seems more likely than some weird wiring fault)

It even seemed to boot some of the dos files from an SD card albeit with some errors.

No VGA yet only composite but it's a start

Regards

James