Icky - Progress

[Icky]

So we have smash through brick walls and stumbling blocks and are now in ironing out stage. I have a few observations so far:

• So far I have been running this all from my bench PSU and only using 5V, not a 12V line in sight.
• I am seeing some interesting things with power. After adding floppy, mouse and keyboard it started to need a lot more juice - up to 1.19 amps.
• At this power I started to see the RS232 not responding as well. Ie. I would type a character on the term and a different one would come out on ST screen
• Keyboard works but sometimes it has spurious repeating of a keys
• The screen flicker - haven't had time to test other monitor due to getting floppy working. I did try Hi-res and it was rock solid.
• Sound has disappeared

[exxos]

Video issues may be because of the scart switch needing 12V ?

RS232, Keyboard.. could well be some interrupt issues with the MFP.. hard to say... Might just need more large caps across the board if it only just started showing issues...

[Icky]

Video issues may be because of the scart switch needing 12V ?

RS232, Keyboard.. could well be some interrupt issues with the MFP.. hard to say... Might just need more large caps across the board if it only just started showing issues...

Just tried original STFM PSU so 12v line is in play.

Still getting screen flashing - I have a feeling it might be the cable. I still need to plug it into another monitor.

[exxos]

Just tried original STFM PSU so 12v line is in play.

Still getting screen flashing - I have a feeling it might be the cable. I still need to plug it into another monitor.

Using CSYNC or H&V sync ? voltages might be a tad to low for modern monitors...

Can you scope the YM outputs ? see if you get activity during sound test..

[Icky]

Using CSYNC or H&V sync ? voltages might be a tad to low for modern monitors...

Can you scope the YM outputs ? see if you get activity during sound test..

From rewiring the cable I remember it its CSYNC.

I will do the YM tomorrow evening - have non-atari things needing my attention :(

[exxos]

This really does beg the question why the pull ups are missing on every Atari schematic.. Falcon below..

As the STF fails without them, shouldn't every Atari every built have the same issue ? :shrug:

Its one of those times where I say "it's a wonder any Atari ever booted" :lol:

EDIT:
oh I tell a lie, it has ONE pull up on WRITE...

EDIT2:
More to the point, why open collector anyway ?

f.JPG

[PhilC]

More interesting than coronation street. :D

Will try the pull ups and hopefully scope the audio tonight myself.

[exxos]

More interesting than coronation street. :D

Indeed!

Will try the pull ups and hopefully scope the audio tonight myself.

:bravo:

It might be worth scoping out some pins around ACIA area, such as (U54) A1 pin 11, A2 pin 8, (U32) pin 3 SNDCS.. (IC2 MFP) pin 48 CS.

[exxos]

I found this diagram...

https://www.atarimax.com/jindroush.atar ... _xf551.gif

sch_xf551.gif

Key part... is the LS 14 (schmitt buffer) not open collector.

Seems "everyone" uses open collector (LS06) but why ?

There must be some other machines out there like the BBC which use the 1772 so we can see what buffers they used ?

[exxos]

:threadjacked:


I took apart a external drive.. and measured the LS06 pins on the connector.. all read the same value (tried both ways with meter probes)

Looks like some bodge on resistors internally.. can't get PCB out to check further :(

IMG_3277.JPG

IMG_3279.JPG

EDIT:

Similar thing on the original bodge boards... I measure 1K (they go to a pull up resistor pack)

IMG_3280.JPG

EDIT2:

MPF920 doesn't seem to have any pull ups..

The MP-F11W drive has 1K..

So I guess this explains these odd issues then. Not all drives have the pull ups. "Atari" ones do.