Falcon clock patch V4 series

[exxos]

Totally remove 47pF? Ok, I can try.
I will try to find where to measure the clock on the expansion port. I'm pretty convinced that the problem sits there.

It should give you sharpter signals.

Where ? On the V4 itself?

Yes..


I quickly connected up my CT60e.. was under a huge layer of dust!

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I am running Falcamp on loop now. I will leave it running for half an hour to see what happens. It's done 4 loops already..

[mikro]

Also, I would definitely lower the CT60 frequency to the 'default' 66 MHz.

[exxos]

Also, I would definitely lower the CT60 frequency to the 'default' 66 MHz.

I concur.

Mine just crashed but that could be because my scope probe slipped but also I don't have a fan on my CPU either and its clocked to 92mhz. It ran for almost half an hour in total anyway.

[exxos]

I measured the clock on the CT60 and its pretty bad actually.

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But it will be likely a lot worse on the Atari patch as it has no series resistance at all.

I will try adding in a 68R and retest tomorrow as it's 11pm here now.

[Swissfalcon]

very interesting. Meanwhile, I just realised that R221 is the one that lead to the expansion bus. And this is what I got on R221 on the V4 itself:

patch V4 R221.jpeg (538.09 KiB) Viewed 641 times

For the records, this is what I have on the V4 PCB on R222

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and on R216

patch V4 R216.jpeg (493.41 KiB) Viewed 641 times

So, either I did a bad measurement on R221, or the signal is like this, and I think that it's the problem.

I will borrow the the oscilloscope tomorrow and do the measurement once again, and update.

I'm failing to see where on the CT60e I have to point the scope, can I ask you a pic?

[exxos]

Those are all expected results on the V4 itself. It's having to deal with the reflections from the motherboard traces. That's why they look the way they do and why series resistors and capacitors are important.

Your sdma clock isn't as sharp as it could be. As joy now works, I'd assume sdma clock is fine now. But removing the 47pf will help with the rise and fall times. Though it will also likely cause ringing. I'm have to use 47pf on my falcon.. but it seems other falcons may need a smaller value. But measurement issues could be a factor. It's hard to tell without measuring the clock with my own scope to see if I get the same results.

The expansion clock looks bad on my falcon with CT60 but I've not had that installed for years. Seems it needs a even higher resistor value . I will try some values tomorrow. It's easy to fit a inline resistor in the wire from the V4 anyway.

The point on the CT60 I marked with black marker pen on my previous images I posted..

R216 , the left wire on the V4 leads to the expansion bus...That is the wire i will add 68R to tomorrow..

[Swissfalcon]

Ok, understood. Oh, I didn’t get the black arrow, sorry
Perfect, I will measure there tomorrow and report. Good night

[Swissfalcon]

R216 , the left wire on the V4 leads to the expansion bus...That is the wire i will add 68R to tomorrow..

R216? Is this schematic wrong then?

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[exxos]

R216 , the left wire on the V4 leads to the expansion bus...That is the wire i will add 68R to tomorrow..

R216? Is this schematic wrong then?
IMG_7105.jpeg

I've not seen that diagram before .. I measured with my meter from R216 resistor as marked on the V4 across the expansion header pins to find the clock.

[Swissfalcon]

Ha, yes, I see 216 on this one. Damn, the first one is definitively wrong.

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