Icky's H4 Mongrel edition build x 2

[PaulJ]

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

Icky, what's going on... that jump looks like Phils dogs got to it.

[Icky]

@PaulJ - soldering iron got a bit aggressive with the jumper when I was desoldering the 75R's

[Icky]

Hmm - I still think there is something not quite right with the video circuit. My board currently has 100R and Caps in series. The colour has got darker but I am getting flickers and and pulsing on the screen. This is using my rock solid monitor / TV. Am going to make a video to show this in action. I have yet to try the 100R and cap combo on the monitor I was getting complete white out.

[Icky]

@exxos has been helping me test out the 1.44 HD Floppy part of the H4.

After initial problems with finding a HD floppy that actually worked and having to format it on my TT. We can confirm that it works, see photo below total bytes add up to 1440508 on the A Drive on the H4.

I'll stick up a guide on how to tomorrow.

IMG_4705.jpeg (82.93 KiB) Viewed 1286 times

[PhilC]

Cool, well done Icky, is it a gal or ATF we will be needing?

[Icky]

@PhilC - you need a GAL22V10C

[PhilC]

Cool, got plenty of those.

[kodak80]

you need a GAL22V10C

Could GAL22V10D or GAL22V10B also be used? Datasheet looks similar. What speed or does this not matter?

[Icky]

Thought I would post a pic of the H4 1.44 HD floppy test rig.

You may notice Flashy Clock V3 (FCV3) is in one of the expansion sockets (not the Flashy Clock socket one as I haven't got round too sorting that out yet). The PLCC CPU has been removed and DIP 68K is in use on the FCV3. In addition there is an extra lead coming out from the FDD drive that is used for the HD select.

IMG_4713.jpeg (169.39 KiB) Viewed 1244 times

[exxos]

as long as you don't make a habit of shoving things in the wrong hole

I may at some point see if I can route the 2 1772 lines which goes via resistors though the gal instead. Might save 2 resistors and could be classed as a bit more eligent I guess.

Incidentaly, the H4 could likely work without the 3 large smt caps. I mean there's enough smaller caps across the board that they may not actually be needed. It would have to be looked into properly though, not just a test of if it boots or not.