working strange : MF2 clone + Mother X4 and other cards..

[talrek]

Well i noticed something strange and i don't understand
I have :
6128+
Mother X4 board
MF2 clone

When i connect the MF2 clone to the 6128+ using a home made cable it doesn't work (turn on, but buttons on MF2 doesn't respond). I tried another cable, same issue.

But when i use a Mother X4 in the middle, the MF2 works !
And if i use a RTC board, XMEM, Megaflash without the mother X4, directly on the cable, it works too ..
Everything work except : MF2 with cable...

The problem is only with a CPC6128+, it works fine on a CPC6128...

Any ideas ? thought it could be the cable, but all other devices works fine

[CraigsBar]

Hmmm, not an is on my plusses with the remake mf2.

[talrek]

I don't understand because it is a new issue, it did work fine before ;-)

[Bryce]

How long is the cable?

Bryce.

[TFM]

I don't understand because it is a new issue, it did work fine before ;-)

Well, here is one possibility: The MF2 card consumes relative much power. Your PSU or monitor gets older, so delivers too few power. When using your MX4 card, you're using an external PSU, so there is enough power.




This was just guessed... 

[Bryce]

This:

And if i use a RTC board, XMEM, Megaflash without the mother X4, directly on the cable, it works too ..

would suggest that it's not a power issue.

Bryce.

[talrek]

Well, here is one possibility: The MF2 card consumes relative much power. Your PSU or monitor gets older, so delivers too few power. When using your MX4 card, you're using an external PSU, so there is enough power.




This was just guessed... 

I don't use any external power supply for the mother X4

How long is the cable?

Bryce.

20-30 cm

[Bryce]

Ok, my guess is that it's a voltage stability problem. The other boards have a 100µf capacitor across the 5V - GND stabilising the voltage at the end of the cable. The MF2 alone doesn't and it's at the end of a 30cm cable. Add a 100µf cap across the supply on the MF2 and see if it then works alone.

Bryce.

[talrek]

Ok i will try. But voltage stability is the same on a "normal" Cpc isn't it ?
Because I haven't this issue on it with the same length...

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[Bryce]

Ok i will try. But voltage stability is the same on a "normal" Cpc isn't it ?
Because I haven't this issue on it with the same length...

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Voltage stability changes with every component you add to the system, so no two systems will be identical. If the ICs on the MF2 are causing noise on the 5V line and no capacitor is near to buffer these, then all sorts of things can happen.

Bryce.

[talrek]

So i didn't add the capacitor to see, but i shortened the cable. And it works. So you were right Bryce.

But i don't understand why it works with a long cable + Mother X4.. there is no capacitor on it, i Guess it is the diodes... 

[Bryce]

[attach=2]

Bryce.

[talrek]

Well i don't have one on mine 

[||C|-|E||]

I am big fan of capacitors to prevent those kind of things. I like to restore old calculators from time to time (I have a small collection) and I always prepare a little external circuit for them, encapsulated in a box, with a voltage regulator, two capacitors and a diode. It is a bit overkill and redundant, but it protects them and allows the old machines to keep calculating if something happens. I found that many of them are very sensitive to current fluctuations: sometimes they reset and some others they just give you the wrong answer  . Of course, I am talking about calculators that require external power supplies  .

[Bryce]

Then it might be that the cable just happened to be the exact length needed to receive so interference from a monitor or some other equipment that was close to your CPC? but I assume you don't own a spectrum analyser and broadband antenna to check the room?

Bryce.

[talrek]

Then it might be that the cable just happened to be the exact length needed to receive so interference from a monitor or some other equipment that was close to your CPC? but I assume you don't own a spectrum analyser and broadband antenna to check the room?

Bryce.

No Indeed 
The important thing is that i have the explanation. Next time i will add a cap, even if it is not in the original. It will be better.

[Bryce]

You can't have too many smoothing caps (most of the time)

Bryce.

[TFM]

Thanks guys, learnt something here - even if i understood not even half of it.