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From: polishedball on 16 Feb 2010 20:32
On Feb 16, 7:26 pm, polishedball <polishedb...(a)gmail.com> wrote:
> I just swapped all the Ram out all 8 from a known good machine and
> still have the same garbled screen.  Ideas?
>
> Thanks
>
> On Feb 16, 2:54 pm, polishedball <polishedb...(a)gmail.com> wrote:
>
>
>
> > On Feb 16, 2:46 pm, Sam <siemappel...(a)quicknet.nl> wrote:
>
> > > Hello John,
>
> > > I've seen your screen pics and I think one of the 4164 RAM chips (UA4
> > > thru UA7 & UB4 thru UB7) is bad.
>
> > > Ray Carlsen wrote:
>
> > > "See if any of the RAM chips (there are eight of them) get warm or
> > > hot... feel each one with the back of your finger after the computer
> > > has run for about 5 minutes. Shorted chips will get hotter than the
> > > others. Note: bad RAM doesn't always get hot."
>
> > > If you feel no difference you can try the "piggyback" trick.
>
> > > Good luck !
>
> > > Regards, SAM
>
> > Thanks will socket them and do some swapping from a working donor C64.
>
> > John

Swapping the Kernal rom does change the color shading on the messed up
screen to a more blue Hue.

From: PK on 17 Feb 2010 02:36
Il 17/02/2010 5.34, polishedball ha scritto:
> Carts don't work, there is a border, and swapping the kernal does
> skew the color but it remains messed up. Ideas?

kernals of C64 and 64SX are a little bit different. They originally show
a different color on border (blue/ light green).
I suppose that's the reason of what you noticed swapping that chip..

Ciao


--




//
\\//http://sites.google.com/site/retrolabels
From: bluebirdpod on 17 Feb 2010 10:29


Have you checked your power supply voltages, The SX-64's MSPS has been
known to cause all kinds of
problems. And does not have much spare capacity, as I know of a SX-64
that had an additional drive installed
along with its controller board to make a artificial DX-64. Its now
located in Bo Zimmers collection and came
from Colorado.

From: polishedball on 17 Feb 2010 13:59
On Feb 17, 10:29 am, bluebirdpod <bluebird...(a)gmail.com> wrote:
> Have you checked your power supply voltages, The SX-64's MSPS has been
> known to cause all kinds of
> problems. And does not have much spare capacity, as I know of a SX-64
> that had an additional drive installed
> along with its controller board to make a artificial DX-64. Its now
> located in Bo Zimmers collection and came
> from Colorado.

Yep 5v 12v and 9vac are all good on meter will scope them tonight for
ripple.

From: Michael on 17 Feb 2010 14:59
On Feb 16, 1:44 pm, polishedball <polishedb...(a)gmail.com> wrote:
> Well my search for an SX-64 brought me to a broken one,  I was
> thinking no problem plenty of repair guides and I was a bench tech for
> 10 years until board swaps became the norm.  I haven't dug in far yet
> but was surprised that the suggested chip swaps did nothing.  I am
> suspecting a logic chip and am curious if anyone has any guesses as
> this unit isn't friendly to work on in it design while hot. Gonna
> download the schematics now.
>
> 1) Have garbage screen with border (maybe the check-board i have read
> about)
> 2) Cartridge slot doesn't appear to work.
> 3) Swapped Vic Chip with known good  Same problem
> 4) Swapped PLA with known Good Same problem
> 5) Swapped character rom Same problem
>
> Screen pics
>
> http://home.comcast.net/~polishedball/screen.jpghttp://home.comcast.net/~polishedball/screen1.jpg
>
> Thanks for any thoughts
>
> John

Look at Ray Carlton's sheets, the SX-64 has a lot missing compaired to
the 64 on. Basically the same issue with chips would affect either.

Since you appear not to have any problem on that document (besides the
PLA) I checked the 64 one. The U numbers might be different but should
be the same chip.

U6 2114 SRAM (COLOR RAM)
Startup screen shows flickering characters with shimmering
colors. check also PLA U17.

U16 CD4066 (generic CMOS quad bilateral switch)
Color problems such as random color "checkerboard" pattern on
screen or no color.

Check by removing SID and seeing if works.
U18 906112-01 (6581) SID
Normal screen. No sound or garbled sound. Mouse or graphics
tablet
pointer stuck or jitters. If shorted, can cause blank or "garbage"
screen.
NOTE: computer will work without a SID plugged in (unplug to check).
This
chip normally runs hot.

U26 74LS373 LOGIC
Startup screen has normal border, but characters are scrambled.

U27 74LS08 (or MOS7712) LOGIC
Normal startup border, but screen full of "garbage" characters.



I would say Yank the SID first and try. Then, if you have access to
another 64, swap the 74LS08 chip. That really looks like what you got.
Where it is in the SX is another story.


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