LarryL’s blog - creating an ATX version of the Phoenix H5

[Cyprian]

@LarryL it looks great

[JezC]

I think mono might work without the video DAC being fitted?
If so, you might be able to test a lot of functionality before you fix/bodge on all those wires ...

[LarryL]

I think mono might work without the video DAC being fitted?
If so, you might be able to test a lot of functionality before you fix/bodge on all those wires ...

Good point, thanks!

Let’s see…

Made some progress today

First the SMT Chips (birdseed already done by JLCPCB)

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Then most of the THT parts (the ports I will save for later)

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[exxos]

I think mono might work without the video DAC being fitted?

I had to check on that myself as I couldn't even remember..

At least on the H5 MONO is buffered and goes to the RGB port as a original machine. But I don't know how closely @LarryL followed that circuit.

The DAC is switched between RGB / MONO for the VGA port mostly. Of course RGB via the DAC also goes to the RGB port.

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I do have some shifter to DAC adapter boards in the store as a backup plan anyway.

[LarryL]

I think mono might work without the video DAC being fitted?

I had to check on that myself as I couldn't even remember..

At least on the H5 MONO is buffered and goes to the RGB port as a original machine. But I don't know how closely @LarryL followed that circuit.

The DAC is switched between RGB / MONO for the VGA port mostly. Of course RGB via the DAC also goes to the RGB port.

I do have some shifter to DAC adapter boards in the store as a backup plan anyway.

Video circuit is very close, indeed identical
I only added the RGB2HDMI buffered pickup in between.

So, yes, Mono goes directly to the DIN13, should work

Good idea with the shifter pickup board - I already have one laying around
And two more DACs have been already ordered at your shop - should arrive during this week
So I can „use“ some DAC chips

[LarryL]

Hi,

did a first "smoke test" this morning (after assembling most of the THT components last night) - of course without any of the THT chips inside

Well, I did not see any smoke, but my bench supply showed, that the board draws 2.5A (I set the max amp to 2.5A, so the bench supply is in saturation).
Voltage drops to 2.5V
Switched off immediately...

So there is definitely a kind of short somewhere.

Tried the same with one of the empty boards: all OK, no current, stable 5V - so problem is not in the main PCB design

Then tried the second PCB with the birdseed (C, R, RN, Reset Chip and two of the smaller logic chips) - now again 2.5A consumption

Measured resistance between 5V and GND:
- populated board: 4k
- birdseed: 7k
- empty PCB: infinite
Doesn't look wrong (the original ATX ST has 2.3k between 5F/GND (no chips, just the passives)

Weired...
Need to do some detailed inspections...
visually I did not find any obvious problems so far
Maybe I disassemble the birdseed components one by one until the problem is gone...

[LarryL]

OK, found the problem.
For some odd reason, I had GND and VCC swapped at the two 74LVC1G04
another area for using bodge wires...

[JezC]

We may need to see more photos of the board with bodge wires in situ!

[LarryL]

We may need to see more photos of the board with bodge wires in situ!

Here we go…

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built in a complete 74LS04 with a few bodge wires

Soldered the wires to a socket and then glued it upside down with tape…

[LarryL]

…you want more bodge wires?

Two more, because I missed up input and output pins of the reset chip :

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