Neo Zemmix Expected Behaviour

Supporter (5)

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

بواسطة ducasp

Paladin (680)

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).

بواسطة Grauw

Ascended (10771)

28-01-2019, 11:32

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

بواسطة jimmydeath

Supporter (5)

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

بواسطة Grauw

Ascended (10771)

28-01-2019, 14:22

Yep attached keyboard does not matter.

بواسطة ducasp

Paladin (680)

30-01-2019, 10:56

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

بواسطة DamnedAngel

Champion (266)

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,

بواسطة jimmydeath

Supporter (5)

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

بواسطة Swami

Expert (90)

22-01-2023, 01:44

Can anyone suggest to me PS/2 keyboards that work with their Zemmix Neo from 8bits4ever. I have three and none of them work. I have a Compaq 5137 (P/N:5118-0989) that has worked once or twice but generally does not.

بواسطة Gregory

Champion (260)

08-03-2023, 23:55

Can somebody explain what the working is of chip U50 74HC4053 on the Zemmix Neo.

As far as i can figure it out. Depending on the state of S1, S2, S3 the signals VGO, VBO and VRO get output to the VGA connector at full voltage or through the voltage dividers VR1, VR2, VR3.
Don't quite understand what the purpose is of this. I thought that the signals going to the VGA connector should be 0.7V max, so it should always be limited by a resistor depending on the output of the digital circuit.
Can somen shed some light on this?
Zemmix Neo schematic

بواسطة hardwaremaker

Master (247)

09-03-2023, 08:33

The U50 is for the scanlines generator for VGA output (switches 2 and 3 on), and the VR's are for the size of the scanlines in every color component. Usually a good setting is all the VR's on the center.