ALPHA MODIFICATIONS

All information relating to the Alpha plus all the WIP threads etc.
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exxos
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ALPHA MODIFICATIONS

Post by exxos » Sun Sep 09, 2018 9:27 pm

Started a new thread for "must do" fixes and mods etc.
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Re: ALPHA MODIFICATIONS

Post by exxos » Sun Sep 09, 2018 9:35 pm

JUMPER PADS
links.jpg
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SJ1 & SJ2 are the 2 solder pads like on the STFM near the blitter. Pads must be shorted when NOT using the blitter, and OPEN when using the blitter. For now I would suggest not fitting the blitter.

SJ5 is the clock line for the CPU, this needs to be soldered to allow 8MHz clock to CPU.

SJ3 & SJ4 Need to both be linked.

(Jumpers were there with intention of adding boosters without cutting tracks at a later date )

Jumper next to the ROM is the TOS104 / TOS102 select line.
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Re: ALPHA MODIFICATIONS

Post by exxos » Mon Sep 10, 2018 10:05 am

RESET FIX

First is the short as found by icky on the reset circuit viewtopic.php?f=19&t=1171#p9633


The red circle shows the resistor shorting out VCC to the highlighted yellow line..
1.JPG
1.JPG (55.25 KiB) Viewed 2409 times

SOLUTION


STEP 1:
s1.JPG
s1.JPG (53.48 KiB) Viewed 2409 times
Cut the tracks on the bottom of the pcb where the yellow lines are.



STEP 2:
s3.JPG
s3.JPG (56.88 KiB) Viewed 2409 times
Solder a wire on the bottom of the PCB to join the pads highlighted with a yellow circle.

DONE:
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Re: ALPHA MODIFICATIONS

Post by Icky » Mon Sep 10, 2018 10:24 pm

exxos wrote:
Mon Sep 10, 2018 10:05 am
If anyone can post a image of this fix then it would help...
As requested two images. Excuse the messy soldering / flux etc on the underside :oops:

IMG_3034.png
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Track cuts are under the wire patch

IMG_3032 (1).png
IMG_3032 (1).png (367.9 KiB) Viewed 2375 times

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Re: ALPHA MODIFICATIONS

Post by exxos » Mon Sep 10, 2018 10:56 pm

Icky wrote:
Mon Sep 10, 2018 10:24 pm
As requested two images. Excuse the messy soldering / flux etc on the underside :oops:
:bravo:
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Re: ALPHA MODIFICATIONS

Post by exxos » Sun Sep 16, 2018 10:30 pm

HSYNC FIX

from here viewtopic.php?f=19&t=1146&start=90#p9961

I ballsed up the Hsync and it needs a fix to bypass the inverter...

d1.JPG
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Re: ALPHA MODIFICATIONS

Post by Icky » Sun Sep 16, 2018 11:19 pm

exxos wrote:
Sun Sep 16, 2018 10:30 pm
HSYNC FIX

from here viewtopic.php?f=19&t=1146&start=90#p9961
I just sat down to start doing some work on the board tonight and thought I would tackle this first.

Fix in place but am still getting horizontal scrolling as per video of boot before fix.

Will take a closer look at the circuit to see whats going on.

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Re: ALPHA MODIFICATIONS

Post by Realloy » Sun Sep 16, 2018 11:55 pm

After cutting the trace on both sides of R920 ,,,, measure between D7 and the cut free R920 i get zero ohm, those two point must go to positive plane in pcb, so i guess no need to move the R920.

And also i noticed that the holes for the PSU is mirrored on the PCB.. Maybe you already know this..

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Re: ALPHA MODIFICATIONS

Post by exxos » Mon Sep 17, 2018 12:10 am

Realloy wrote:
Sun Sep 16, 2018 11:55 pm
After cutting the trace on both sides of R920 ,,,, measure between D7 and the cut free R920 i get zero ohm, those two point must go to positive plane in pcb, so i guess no need to move the R920.
ahh yep, The left link wire isn't needed as the resistor itself actually connects to vcc.. will update the info...
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Re: ALPHA MODIFICATIONS

Post by Realloy » Mon Sep 17, 2018 8:33 pm

i can see all the chips have a decoupling capacitor,,, but what about BAD DMA ? is there one and where? or is it not necessary?

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