Simple diagnostics cartridge

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Door Alexey

Guardian (3092)

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16-01-2021, 16:12

During the last year I've seen numerous messages from MSX users, whose computers stopped working after being removed from the storage or after another power cycle. Many people complained about black screens or about total power failure. It's a known fact that RAM and other elements may go bad during storage or at power-on. Diagnosing those problems usually starts from checking the power rails, clock signals, reset signal's state and activity on data and address bus. It has been decided to create a simple diagnostics cartridge that could help to perform the initial check of a computer and rule out the most common problems.

The cartridge named "iBolit" (https://en.wikipedia.org/wiki/Doctor_Aybolit) was created using the GAL22V10 programmable logic chips, LED assemblies and volt/ammeters from the PC's USB socket tester dongles. There's an additional cartridge slot installed on the top of iBolit cartridge. There one can insert any cartridge including the one with MSX diagnostics ROM (there are a few, but it would be nice to create a universal one). The GAL firmware is very primitive - if there's a high level on input, the LED connected to the output will light up. The cartridge is fairly cheap to build - maximum 12-15 Euro and is relatively easy to assemble.

The drawback is that some signals switch from high to low very fast (for example CLK), so it's impossible to see distinct LED blinking for such signals - the LED will just be lit and the brightness will depend on the frequency. With the current design it's not possible to make the blinking more visible. But that's not planned. It's enough to see that there's an activity on the signal.

A few photos of the prototype:

A few videos of prototype's test:

http://podrezov.com/ibolit/testproto1.mp4
http://podrezov.com/ibolit/testproto2.mp4
http://podrezov.com/ibolit/testproto3.mp4

The project will be put into the RBSC's repository when it's ready. No mass-production is planned at the moment.

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Van Louthrax

Prophet (2400)

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18-01-2021, 19:17

Rhaaaa, that looks awesome with leds and all Running Naked in a Field of Flowers !

Almost whish I had a faulty MSX to use this Smile

Van ray2day

Hero (657)

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18-01-2021, 19:36

Nice Cool

Van Alexey

Guardian (3092)

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19-01-2021, 10:12

I've got the inspiration from this project: https://www.youtube.com/watch?v=Kw80Qpbl3FU

Van lintweaker

Champion (400)

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19-01-2021, 10:52

Haha, blinkenlights to the max! No issues with powering so many leds?

Van VegaVegas

Resident (59)

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19-01-2021, 12:36

So this is just an LED cartridge that can indicate bus activity?? Interesting but I imagine a diagnostic cart would have some sort of mini program that checks parts in the machine, for instance scanning RAM and checking if it's defective. Something an ordinary user can use

Van Alexey

Guardian (3092)

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19-01-2021, 13:39

lintweaker wrote:

Haha, blinkenlights to the max! No issues with powering so many leds?

Nope. The GAL chip serves as the buffer, so the LEDs don't draw current from the signal lines.

Van Alexey

Guardian (3092)

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19-01-2021, 13:46

VegaVegas wrote:

So this is just an LED cartridge that can indicate bus activity?? Interesting but I imagine a diagnostic cart would have some sort of mini program that checks parts in the machine, for instance scanning RAM and checking if it's defective. Something an ordinary user can use

We had plans for such complex diagnostics cartridge. But at the moment we are busy with another interesting project as well as with the tasks of improving Carnivore2. RAM, VRAM and other components may be tested with various utilities. There's even a diagnostics ROM that you can put onto the cartridge and use it with the iBolit or in a separate slot (but the latest version of MSX diagnostics is quite buggy).

I think we should not only make competitions who creates the best game or demo, but join efforts in creation of the universal diagnostics ROM that could help to identify common problems in our MSX machines and report them even if there's no audio and video outputs from a computer. Sadly, my proposal to create such a project was not taken seriously.

Van lintweaker

Champion (400)

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19-01-2021, 13:44

Alexey wrote:
lintweaker wrote:

Haha, blinkenlights to the max! No issues with powering so many leds?

Nope. The GAL chip serves as the buffer, so the LEDs don't draw current from the signal lines.

Thanks, I also meant the overall current draw. With all the (potential) LEDs lighting up. I probably could draw quite some current (a few 100s mAs).

Van Alexey

Guardian (3092)

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19-01-2021, 13:56

lintweaker wrote:
Alexey wrote:
lintweaker wrote:

Haha, blinkenlights to the max! No issues with powering so many leds?

Nope. The GAL chip serves as the buffer, so the LEDs don't draw current from the signal lines.

Thanks, I also meant the overall current draw. With all the (potential) LEDs lighting up. I probably could draw quite some current (a few 100s mAs).

I don't have the second cartridge assembled yet, so I can't measure the consumption. But I will. The current for each LED is limited with 1kOhm resistors, so it's 5mA per LED. 39 LEDs draw less than 200mA. Then there are 4 GALs with at least 20mA. So it should not be more that 250-280mA per slot. Unless I made a mistake in my calculations.

Van VegaVegas

Resident (59)

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19-01-2021, 18:33

If the request to make a diagnostic ROM was ignored then it really shouldn't. It could reduce "my MSX suddenly stopped working" topics up to 30%

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