Icky's H4 Mongrel edition build x 2

[PhilC]

At least yours works, I've probably a whole load to find.

[PaulJ]

@Icky I did rename FDCS to HDCS but traced it around and nothing different. I can't see anything wrong anywhere. Can only assume there's a bad solder job somewhere causing it all.

If there's a bad solder job to be found its probably mine.

Il'll go over the board again.

Unlikely we have two bad solder issues that exhibit the same fault exactly with everything else working.. My money is the board but we won't know until we find something. Hey not complaining, the board was virtually perfect and all signals on the scope look great!

[exxos]

Has me beat.

Other than, as Icky said, I used a NOR as a inverter for the MFP input, swapped a LS04 for a LS06 (hence the pull up on HDRQ). I also renamed FDINT to HDINT, but all points look connected the same as the Alpha.

Aside from the buffers (the DMA buffer was tested on a bodge board and literally copy-pasted over) even so, Icky says it still not working jumpered.

The only thing I can think of is if the propagation delays of the chips I swapped about are the issue.. But there isn't any real different anyway. Both swaps are still inverters, so no logic function changes.

EDIT:

Been around it all again, still don't see anything wrong. compared it to the Alpha and STF diagram, unless I am going blind, just nothing wrong circuit wise that I can see.

The only other difference is the case of the DB19 isn't grounded on the H4 ? I don't have a board here to check.

[exxos]

@Icky You mention the brightness issue earlier, was you using the RGB port or VGA ? TV or Monitor ?

[Icky]

@exxos - Am using ST Monitor socket with socket to SCART cable to both a TV and monitor TV.

[exxos]

@exxos - Am using ST Monitor socket with socket to SCART cable to both a TV and monitor TV.

So how come bridging the caps originally when we tested it had no effect, but now all of a sudden does ?!

I really need my H4 to come back so I can try it on my monitor

[Icky]

@exxos - I remember doing it and it didn't make a difference on the ALPHA, see bridges over caps

IMG_3353.jpeg (157.3 KiB) Viewed 3959 times

[exxos]

@exxos - I remember doing it and it didn't make a difference on the ALPHA, see bridges over caps

The circuit is identical, so I don't get what changed in all this

[Icky]

Finally got round to looking at the video and changing the 75Rs for 100R with caps in series. Below is a pic of the hack to add the 100R and caps.

IMG_4631.jpeg (196.23 KiB) Viewed 3923 times

Below is a comparison of the original H4 circuit on the left and the revised 100R with caps in series on the right. As you can see its darker but still not as dark as the original ST. I will get a comparison pic of the original a bit later.

H4-Normal and Caps.png (989.04 KiB) Viewed 3923 times

[PhilC]

Looks about the same as the improvement I got. I'm planning on upping the resistor values when I'm back.