exxos's Atari, Amiga & retro forum

I found another lug that would need cutting off of an original ST case to allow the board to fit if thats what you want to achieve.

So that makes two lugs (see previous one mentioned https://www.exxosforum.co.uk/forum/viewt ... 335#p29006) and now the H4 board will fit in a case with the bottom shielding in place

I have been going round H4 with a fine tooth comb, well magnifying glass and microscope actually and found that I had a very small hairline solder bridge on the U2. Solder issues are the usual cause of problems when building these boards as I found on the ALPHA with missed pins not being soldered, bad joints and shorts

Below is a fuzzy pic of the U2 where the solder bridge is between Pin 4 -5 ROM_OE and VCC

Here is the benchmark of my H4 running with Blitter


To help with a few questions around the DAC from @derkom, the DAC does get hot, I measured 57 degrees. I do notice on my monitor its very bright compared to an original ST. I also have found on another monitor where an original ST is fine the H4 comes out like the below picture, so @exxos and I are investigating.


Measuring the RED out on the H4 and an original ST the scoping is as follows:

H4 Original

Icky wrote: ↑Wed Dec 04, 2019 10:20 pm To help with a few questions around the DAC from @derkom, the DAC does get hot, I measured 57 degrees.

Thanks for this. I haven't measured, but the finger test on mine agrees with your figure.

Yeah the DAC is driving basically a few ohms resistance, so its gonna suck some power and dissipate some heat.

@Icky Needs to add some caps in series with the 75R resistors (You may have the 100uF ceramics caps from the DAC bodge board ?) This will adjust the DC offset to see if that's the issue.

Secondly , assuming the caps makes no odds, then it may well need some higher value resistors to simply cut the brightness down. Its hard to tell if this is a issue until others mention it. Though the DAC circuit is pretty much the same as the Falcon's, and if anything, the Falcon video is darker than my STFM's. So not really sure why Icky has the opposite to what I have seen.

@Icky Looking when you was testing the DAC board, you actually had a darker image than the remake, but on the H4 (Which is the same DAC circuit) its now brighter .....

https://www.exxosforum.co.uk/forum/viewt ... 250#p14758

@exxos - Yeah odd as the cable and monitor are the same for the ALPHA and H4 haven't changed them.

@exxos - think i may of found a difference.

Just went back to the ALPHA and the RGB from the DAC board may of gone through a 33R to the monitor socket so we had an additional 33R in series.

See here the RED line from the DAC board went into R19

https://www.exxosforum.co.uk/forum/viewt ... 220#p14718

EDIT: starting to doubt myself though as I think it may not of been going through the 33R's. It was awhile ago and I have stripped that part out of the ALPHA.

Icky wrote: ↑Wed Dec 04, 2019 11:24 pm EDIT: starting to doubt myself though as I think it may not of been going through the 33R's. It was awhile ago and I have stripped that part out of the ALPHA.

I can't remember if it goes though it on my board or not, will try and look tomorrow... though I Guess you could add another 33R in there, or swap for 100R to try anyway.

Icky wrote: ↑Wed Dec 04, 2019 10:20 pm

Congrats Icky, guess you didn't use any the magic smoke either. Yes your image looks like mine, pretty washed out.