ALPHA MODIFICATIONS

https://www.youtube.com/user/exxosuk · Post by **exxos** » Sun Sep 09, 2018 9:27 pm

Started a new thread for "must do" fixes and mods etc.

https://www.youtube.com/user/exxosuk · Post by **exxos** » Sun Sep 09, 2018 9:35 pm

JUMPER PADS

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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.

https://www.youtube.com/user/exxosuk · 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..

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SOLUTION

STEP 1:

: s1.JPG (53.48 KiB) Viewed 2410 times

Cut the tracks on the bottom of the pcb where the yellow lines are.

STEP 2:

: s3.JPG (56.88 KiB) Viewed 2410 times

Solder a wire on the bottom of the PCB to join the pads highlighted with a yellow circle.

DONE:

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

: IMG_3034.png (419.7 KiB) Viewed 2376 times

Track cuts are under the wire patch

: IMG_3032 (1).png (367.9 KiB) Viewed 2376 times

https://www.youtube.com/user/exxosuk · 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

https://www.youtube.com/user/exxosuk · 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 (49.49 KiB) Viewed 2274 times

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.

Realloy · 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..

https://www.youtube.com/user/exxosuk · 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...

Realloy · 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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