H4 FIXES & KNOWN ISSUES

[exxos]

4MB SIMM RAM FIX

A small oops on my part.. While ST RAS0 = SIMM RAS0, ST RAS1 = SIMM RAS2... This would mean RAM over 2MB probably wouldn't be found. This doesn't affect the Falcon RAM board in anyway.

A small bodge wire should fix the issue.

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[exxos]

RS238 FIX

PaulJ found this issue.. https://www.exxosforum.co.uk/forum/viewt ... 736#p29736

Looks like when I renamed some pins (I would have deleted the signal to avoid it remaining everything else connected as well) and connected it back up, I put it on the wrong pin This would cause the RS232 port not to accept data (but would still send data) .

The current issue is below...Where pin 7 & 20 are the wrong.

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Corrected pinout.

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The red track needs cutting..

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and a bodge wire connecting on the new red track.

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[exxos]

DMA FIX

This issue and fix haven't yet been known of, or verified either way (other than me, who hasn't got a H4 yet )

These resistors seem to cause odd issues when ultrasatan is plugged in, it generally causes the floppy drive to malfunction.

Change the 2x 1K resistors for 470R.

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[exxos]

DAC FIX

There was a bit of a discussion about this in this thread https://www.exxosforum.co.uk/forum/viewt ... =78&t=2384

Basically three pins need isolating on the DAC IC as highlighted below...

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Using a exxos pin fertler tool (c) exxos 2020 I heated up the pin and pulled it upwards with the tool...

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[JezC]

Looking through these in preparation for finishing my part-assembled H4/starting the bare PCB one...

I thought there was another fix relating to the buffer on the DMA & a bodge board has been designed for it...but there is nothing about it in this thread...

I'm referring to this
https://www.exxosforum.co.uk/forum/viewt ... =30#p30306

I think there is another fix by just removing the buffer & linking it out...?

I'm just wanting to get any rework at the board level done before I start adding more components to the mix...

[exxos]

@JezC Linking over the buffer was the "debugging" of the issue, aka a temporary bodge fix... The patch board is the proper fix, so that is the only one which should be done.

[JezC]

Ok, great. I'll see about ordering a couple but will have to follow the bodge for now.

Thanks

[exxos]

Ok, great. I'll see about ordering a couple but will have to follow the bodge for now.

It is only needed if you want to use the DMA port..

[JezC]

Yes, I have a few mechanical SCSI hard drives and will need at least one of them for my music/MIDI SW.

So I know to order some for the future but bodge for initial bring-up.

[troed]

DMA FIX

This issue and fix haven't yet been known of, or verified either way (other than me, who hasn't got a H4 yet )

These resistors seem to cause odd issues when ultrasatan is plugged in, it generally causes the floppy drive to malfunction.

Change the 2x 1K resistors for 470R.

Maybe changing this in the BOM? I just soldered the 1Ks in according to that list - then saw this

/Troed