| Help on finding c64 fault [message #163421] |
Mon, 15 May 2006 11:06  |
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Originally posted by: Jools Smyth
Hi,
One of my c64's has a problem which I would like to fix.
It powers up normally, and seems fine, but demos/games all have corrupt
graphics. (As though stuff has been jumbled around on the screen. The
computer does not crash. Only the display is messed. In the startup
character mode everything is fine (including sprites).
I have ran some tests. Ram tested fine, and I have replaced both the PLA and
the VIC and the same problem occurs. I'm not sure what to switch next, does
anyone have any idea ?
I've read this document:
http://personalpages.tds.net/~rcarlsen/cbm/C64-IC.txt
Nothing really stands out.
Perhaps
U16 CD4066 (generic CMOS quad bilateral switch)
Color problems such as random color "checkerboard" pattern on screen
or no color.
anyone else have any ideas? Or what I can test? Is it possible its a faulty
socket for example ?
Best Regards
Jools
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| Re: Help on finding c64 fault [message #163433 is a reply to message #163421] |
Mon, 15 May 2006 16:33  |
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Originally posted by: Wolfgang fartbubble
Jools Smyth wrote:
> Hi,
>
> One of my c64's has a problem which I would like to fix.
> It powers up normally, and seems fine, but demos/games all have corrupt
> graphics. (As though stuff has been jumbled around on the screen. The
> computer does not crash. Only the display is messed. In the startup
> character mode everything is fine (including sprites).
>
> I have ran some tests. Ram tested fine, and I have replaced both the PLA and
> the VIC and the same problem occurs. I'm not sure what to switch next, does
> anyone have any idea ?
>
> I've read this document:
>
> http://personalpages.tds.net/~rcarlsen/cbm/C64-IC.txt
>
> Nothing really stands out.
>
> Perhaps
>
> U16 CD4066 (generic CMOS quad bilateral switch)
> Color problems such as random color "checkerboard" pattern on screen
> or no color.
>
> anyone else have any ideas? Or what I can test? Is it possible its a faulty
> socket for example ?
>
> Best Regards
>
> Jools
It may well be the Character ROM.
Mike.
--
http://uk.geocities.com/swift240/index.html
http://commodore16.bravehost.com
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| Re: Help on finding c64 fault [message #163437 is a reply to message #163433] |
Mon, 15 May 2006 19:59 |
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Originally posted by: Jools Smyth
Wolfgang fartbubble wrote:
> It may well be the Character ROM.
That would make sense, but could a fault with the character rom cause the
effects ive said. it does look like everything is jumbled in 8x8 squares,
but only in multicolour modes etc ? (as i said everything is fine on
bootup)
I'm a bit of a novice at this. I just bought some sockets etc, and will
replace the character rom and test anyway.
Best Regards
Jools
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| Re: Help on finding c64 fault [message #163441 is a reply to message #163421] |
Mon, 15 May 2006 21:56 |
Snogpitch
Messages: 185
Registered: September 2012
Karma: 0
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Senior Member |
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Are you sure the power supply is good? Sounds like a problem happens after
the machine has been on for a while. Run your tests again over a long
period of time, like a few hours.
What happens if you use a cartridge game?
Could the demos be a different video standard than the machine? Pal vs NTSC
On 5/15/06 11:06 AM, in article 4468991c$0$2590$db0fefd9@news.zen.co.uk,
"Jools Smyth" <buzz@totem.fix.no> wrote:
> Hi,
>
> One of my c64's has a problem which I would like to fix.
> It powers up normally, and seems fine, but demos/games all have corrupt
> graphics. (As though stuff has been jumbled around on the screen. The
> computer does not crash. Only the display is messed. In the startup
> character mode everything is fine (including sprites).
>
> I have ran some tests. Ram tested fine, and I have replaced both the PLA and
> the VIC and the same problem occurs. I'm not sure what to switch next, does
> anyone have any idea ?
>
> I've read this document:
>
> http://personalpages.tds.net/~rcarlsen/cbm/C64-IC.txt
>
> Nothing really stands out.
>
> Perhaps
>
> U16 CD4066 (generic CMOS quad bilateral switch)
> Color problems such as random color "checkerboard" pattern on screen
> or no color.
>
> anyone else have any ideas? Or what I can test? Is it possible its a faulty
> socket for example ?
>
> Best Regards
>
> Jools
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| Re: Help on finding c64 fault [message #163442 is a reply to message #163441] |
Mon, 15 May 2006 22:27 |
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Originally posted by: Jools Smyth
Snogpitch wrote:
> Are you sure the power supply is good? Sounds like a problem happens
> after
> the machine has been on for a while. Run your tests again over a long
> period of time, like a few hours.
I've tested with other power supplies. The problem is consistant, with
anything that does something graphically (not using the default character
mode)
> What happens if you use a cartridge game?
I will check this. (I assume this is to rule out memory issues perhaps or ?)
> Could the demos be a different video standard than the machine? Pal vs
> NTSC
Both machine and software I tested with is pal.
Best Regards
Jools
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| Re: Help on finding c64 fault [message #163458 is a reply to message #163421] |
Tue, 16 May 2006 11:15 |
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Originally posted by: pbdelete
Jools Smyth <buzz@totem.fix.no> wrote:
> Hi,
> One of my c64's has a problem which I would like to fix.
> It powers up normally, and seems fine, but demos/games all have corrupt
> graphics. (As though stuff has been jumbled around on the screen. The
> computer does not crash. Only the display is messed. In the startup
> character mode everything is fine (including sprites).
> I have ran some tests. Ram tested fine, and I have replaced both the PLA and
> the VIC and the same problem occurs. I'm not sure what to switch next, does
> anyone have any idea ?
Definitly sounds as graphics chip is involved or something it relies on.
You should be able to test character rom with software.
RAM already tested.
Beware of heat, emc and power supply issues.
Look at the schematic for any videochip dependency culprints =)
(shit in -> shit out :)
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| Re: Help on finding c64 fault [message #163465 is a reply to message #163458] |
Tue, 16 May 2006 15:22 |
Pasi Ojala
Messages: 151
Registered: March 2012
Karma: 0
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Senior Member |
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On 2006-05-16, pbdelete@spamnuke.ludd.luthdelete.se.invalid <pbdelete@spamnuke.ludd.luthdelete.se.invalid> wrote:
> Jools Smyth <buzz@totem.fix.no> wrote:
>> computer does not crash. Only the display is messed. In the startup
>> character mode everything is fine (including sprites).
> Definitly sounds as graphics chip is involved or something it relies on.
Hey, you are right, I think it may be one of the CIA chips, which
selects the VIC video banks. Specifically CIA#2, which also handles
the serial bus.
If he swaps the CIA's, the keyboard will not fully work, but
the demos should..
-Pasi
--
"You are a very interesting study, as much as Rand, in your own way. And
young Mat. Could I only split myself into three, I would latch one onto
each of you and follow you every moment of the day and night even if I
had to marry you." -- Alanna Sedai in The Wheel of Time:"The Shadow Rising"
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| Re: Help on finding c64 fault [message #163470 is a reply to message #163442] |
Tue, 16 May 2006 19:41 |
Snogpitch
Messages: 185
Registered: September 2012
Karma: 0
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Senior Member |
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Eliminates the possibility that the drive is causing the problem, along with
the cabling, along with the CIA it relies on to transfer data reliably.
My next guess would be the 6510, if it fails the cartridge test.
It would be a lot easier if you could hook up a diag harness to that.
On 5/15/06 10:27 PM, in article 446938d6$0$206$db0fefd9@news.zen.co.uk,
"Jools Smyth" <buzz@totem.fix.no> wrote:
>
>> What happens if you use a cartridge game?
>
> I will check this. (I assume this is to rule out memory issues perhaps or ?)
>
> Best Regards
>
> Jools
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| Re: Help on finding c64 fault [message #163471 is a reply to message #163470] |
Tue, 16 May 2006 21:08 |
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Originally posted by: Jools Smyth
Snogpitch wrote:
> Eliminates the possibility that the drive is causing the problem, along
> with the cabling, along with the CIA it relies on to transfer data
> reliably.
Changed cia's. Same problem. Carts also have the same problem.
> My next guess would be the 6510, if it fails the cartridge test.
Switched 6510. No change.
> It would be a lot easier if you could hook up a diag harness to that.
? Now you've lost me :)
Best Regards
Jools
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| Re: Help on finding c64 fault [message #163472 is a reply to message #163465] |
Tue, 16 May 2006 21:10 |
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Originally posted by: Jools Smyth
Pasi Ojala wrote:
> Hey, you are right, I think it may be one of the CIA chips, which
> selects the VIC video banks. Specifically CIA#2, which also handles
> the serial bus.
> If he swaps the CIA's, the keyboard will not fully work, but
> the demos should..
Switched them and the same problem :/
I tested some more software. It doesn't effect everything. For example the
demo krestology. The first screen with the crest logo and text is fine.
Then next screen with the mermaid ifli (or something) is jumbled up.
Best Regards
Jools
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| Re: Help on finding c64 fault [message #163496 is a reply to message #163472] |
Wed, 17 May 2006 02:50 |
dowcom
Messages: 773
Registered: July 2003
Karma: 0
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Senior Member |
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Group: comp.sys.cbm Date: Wed, May 17, 2006, 2:10am (CDT+6) From:
buzz@totem.fix.no (Jools Smyth)
script:
> I tested some more software. It doesn't effect >everything. For example
the demo krestology. The >first screen with the crest logo and text is
fine. >Then next screen with the mermaid ifli (or >something) is jumbled
up.
That may rule out the only idea that I have had:
The IBM PC used 4K for monochrome text, or 16K for CGA. Maybe the 64
uses only 1K for text, and 4K for graphics. Maybe the fault is in the
other 3K.
Forgot to check my PRG to see if this is even possible.
salaam,
dowcom
To e-mail me, add the character zero to "dowcom". i.e.:
dowcom(zero)(at)webtv(dot)net.
--
http://community.webtv.net/dowcom/DOWCOMSAMSTRADGUIDE
MSWindows is television,
Linux is radar.
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| Re: Help on finding c64 fault [message #163499 is a reply to message #163442] |
Wed, 17 May 2006 07:42 |
Laust Brock-Nannestad
Messages: 110
Registered: July 2012
Karma: 0
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Senior Member |
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Jools Smyth <buzz@totem.fix.no> wrote:
> I've tested with other power supplies. The problem is consistant, with
> anything that does something graphically (not using the default character
> mode)
Have you tested/measured the power inside the 64? It generates 5V/12V
via voltage regulators as well.
Regards,
Laust
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| Re: Help on finding c64 fault [message #163507 is a reply to message #163499] |
Wed, 17 May 2006 12:23 |
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Originally posted by: Jools Smyth
Laust Brock-Nannestad wrote:
> Jools Smyth <buzz@totem.fix.no> wrote:
>
>> I've tested with other power supplies. The problem is consistant, with
>> anything that does something graphically (not using the default character
>> mode)
>
> Have you tested/measured the power inside the 64? It generates 5V/12V
> via voltage regulators as well.
I will check that.
Thanks.
Best Regards
Jools
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| Re: Help on finding c64 fault [message #163522 is a reply to message #163421] |
Wed, 17 May 2006 18:57 |
Decimal Cat
Messages: 33
Registered: July 2003
Karma: 0
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Member |
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Jools, have you checked out the RAM chips? If it only happens with some
software I suppose it's possible things are getting scrambled in the
DRAMs... an easy way to test this is to see if any of them are getting
unusually warm. If they are, they've probably gone to the big burnout in the
sky.. on the older C64 boards there were upwards of 8? DRAMs, while on the
newer 'shortboard' edition found only in the 64C, there were only two. I'd
say it had to do with the color circuitry/VIC support too, but since you've
tested all that..
When the impossible is eliminated, the improbable remains... :)
--Decimal Cat
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| Re: Help on finding c64 fault [message #163523 is a reply to message #163522] |
Wed, 17 May 2006 19:11 |
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Originally posted by: Jools Smyth
Decimal Cat wrote:
> Jools, have you checked out the RAM chips? If it only happens with some
> software I suppose it's possible things are getting scrambled in the
> DRAMs... an easy way to test this is to see if any of them are getting
> unusually warm. If they are, they've probably gone to the big burnout in
> the sky.. on the older C64 boards there were upwards of 8? DRAMs, while on
> the newer 'shortboard' edition found only in the 64C, there were only two.
> I'd say it had to do with the color circuitry/VIC support too, but since
> you've tested all that..
Thanks. Actually I have a new plan. The c64 in question is a bit different
from my others in the fact that most of the large chips are socketed.
However the problem is not with them, so I plan to install sockets for
everychip :-) If I get it working, it will be easy in the future to replace
parts. I just spent 1 hour today unsoldering a pia from another c64
(hopefully to fix a serial issue), and I am feeling more confidant after
this exercise.. Although a friend told me I did it the hard way and lent me
from braid he said will make it easier - I will check, but I am drunk
now :D
Thanks for the help everyone. I will let you know my progress.
On a more positive note (sort of), I bought a c128D recently. It seemed
fine, but after 10 mins demos were crashing, although it booted fine. I
tested the voltages - everything was ok. I reseated the chips, but the
problem still happened. I suspected the 40col VIC, so after it was crashing
I sprayed some alchohol fluid on it, which cooled it, and it worked again.
I installed 2 small heatsinks on the VIC, and a case fan, and the 10 mins
went to around 1 hours before problems, but still crashes. Obviously the
VIC is technically broken, but works whilst still cool. I have now
installed an other fan flowing onto the heatsink (like a hd cooler), and
the machine has remained stable all day.. Great!! Of course, the chip is
obviously poorly, but at least it is working for now.
Actually after running for 6 hours, the VIC is cool to the touch!
I'm on the lookout for a c128 PAL VIC though if anyone has one :)
Best Regards
Jools
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| Re: Help on finding c64 fault [message #163664 is a reply to message #163507] |
Fri, 19 May 2006 18:24 |
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Originally posted by: Jools Smyth
I haven't fixed the mentioned c64 yet, but I have just repaired another one.
The IEC Serial was not working. I suspects U2 (6526). I unsoldered it,
soldered in a socket, and put another 6526 in place. And everything worked!
Running some great demos the machine now. :-)
Best Regards
Jools
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| Re: Help on finding c64 fault [message #163706 is a reply to message #163421] |
Sat, 20 May 2006 07:15 |
Scott McDonnell
Messages: 54
Registered: July 2003
Karma: 0
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Member |
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"Jools Smyth" <buzz@totem.fix.no> wrote in message
news:4468991c$0$2590$db0fefd9@news.zen.co.uk...
> Hi,
>
> One of my c64's has a problem which I would like to fix.
> It powers up normally, and seems fine, but demos/games all have corrupt
> graphics. (As though stuff has been jumbled around on the screen. The
> computer does not crash. Only the display is messed. In the startup
> character mode everything is fine (including sprites).
>
> I have ran some tests. Ram tested fine, and I have replaced both the PLA
> and
> the VIC and the same problem occurs. I'm not sure what to switch next,
> does
> anyone have any idea ?
>
> I've read this document:
>
> http://personalpages.tds.net/~rcarlsen/cbm/C64-IC.txt
>
> Nothing really stands out.
>
> Perhaps
>
> U16 CD4066 (generic CMOS quad bilateral switch)
> Color problems such as random color "checkerboard" pattern on screen
> or no color.
>
> anyone else have any ideas? Or what I can test? Is it possible its a
> faulty
> socket for example ?
>
> Best Regards
>
> Jools
You mention that you checked the 'RAM' but did you check the 'COLOR RAM'?
That would be the 2114 (U5?...looking at a crappy schematic right now)
static RAM hanging off the VIC. This is where screen space is stored. I
would expect that this would affect text as well, but as someone else
pointed out 1K is used for text and all 4K is used for bitmaps. That alone
would point at the address lines mentioned below since that remaining 3K is
addressed by the VIC directly. So RAM, address lines from VIC, and bus
abritration (U27) in that (backwards) troubleshooting order. Details below.
The 8x8 block thing would be normal because that is how the C64 uses the
screenspace in any mode, this is done in the first 1K of color RAM. The
first 1K would be the bitmap - just ON/OFF info on the pixels. The bitplanes
(3 bits per pixel of color, 1 bit for background/foreground?) are handled in
the remaining 3K and this 3K is addressed entirely by the VIC itself.
Perhaps a simple test would be to try to just display multi-colored text on
the screen. I imagine the result would be the text, but not multicolored
unless the failure was catastrophic enough to mess up the whole screen on
the attempt, which I doubt.
The easiest (only?) way I can think of to FULLY test the color RAM would be
the same way as your fault (ie.. put known good data in and visually look at
the results.) But since several things happen in between and you don't
easily have full control of the RAM, it could point at other failures as
well. BTW do the pixels themselves change color over time? My vote is on
replacing that component since it is cheap, easy to find, and RAM has a
(very long but) limited lifespan. If it doesn't clear up, I would start
looking at the address lines coming from the VIC itself (A8 to A11 on the
VIC only) to the color RAM, which is more likely but harder to diagnose. Did
you or someone else socket the VIC before this happened? Bad solder joints?
The next culprit would be U27 74LS08 2 input AND gate used for bus
abritration so that the CPU and VIC are not trying to access the color RAM
at the same time. And finally (U15?...crappy schematic again) which is a
74LS239 2-to-4 multiplexer which aids the PLA in address decoding, which is
the least likely cause.
Of course when all else fails, check continuity on all the signal lines
involved in the above circuitry AND look for poor solder joints at the pins
involved. Do both, because you might measure continuity at the solder
joints, but the solder joint might not be making good contact with the pins
themselves. A dirty iron or bad solder, or even not enough time/heat can
leave a nice crud layer between the solder and the pin. I see this all the
time in my line of work (electronics tech at a defense contractor, no
less!!)
Hope that helps. Please reply to the group when you have it finally fixed as
this really helps people in the future when they are trying to search to
solve thier own problems. Too many people just disappear without the results
and leaves people hanging that are searching for answers (not pointing that
statement at you, just in general.)
Scott McDonnell
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| Re: Help on finding c64 fault [message #163708 is a reply to message #163706] |
Sat, 20 May 2006 07:41 |
Scott McDonnell
Messages: 54
Registered: July 2003
Karma: 0
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Member |
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"Scott McDonnell" <netsamurai@comcast.net> wrote in message
news:VaqdnXqdIN7aZ_PZnZ2dnUVZ_vqdnZ2d@comcast.com...
>
> The 8x8 block thing would be normal because that is how the C64 uses the
> screenspace in any mode, this is done in the first 1K of color RAM. The
> first 1K would be the bitmap - just ON/OFF info on the pixels. The
> bitplanes (3 bits per pixel of color, 1 bit for background/foreground?)
> are handled in the remaining 3K and this 3K is addressed entirely by the
> VIC itself. Perhaps a simple test would be to try to just display
> multi-colored text on the screen. I imagine the result would be the text,
> but not multicolored unless the failure was catastrophic enough to mess up
> the whole screen on the attempt, which I doubt.
Hmm, doing some calculations, something doesn't seem right with my
explaination above. 1 bit per pixel (on/off) for 320x200 would need almost
the entire 64K, so that isn't possible. However, 25x40 (character space)
fits nicely into the 1024 bit space (with 24 bits left over) So the 'bitmap'
itself can't fit into this space at all, only color information for the 8x8
block. 4 bitsx25columnsx40rows would yield 4000, leaving 96 bits of the
color RAM (unused or used?) This leads me to believe the character ROM
itself can handle simple one color text (bg/fg) all on it's own and bad
color ram would have NO affect at all on this type of text display. The
background/foreground colors are registers in the VIC itself.
Anyway, this is mostly acedemic and I am going off the schematic only right
now. It isn't worth it to drag out the references since the diagnosis is the
same, though it now makes the color RAM itself the MOST likely suspect. Chip
selection of the color RAM is still a high possibility. So the
troubleshooting steps mentioned in my reply remain valid. It appears that
the CPU has direct access to the first 1K of color RAM, but testing that
with code would probably be meaningless because it would not really isolate
the cause, only highlight the symptom which you already know.
Scott McDonnell
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| Re: Help on finding c64 fault [message #163732 is a reply to message #163708] |
Sat, 20 May 2006 10:38 |
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Originally posted by: Papabear
Scott McDonnell wrote:
> "Scott McDonnell" <netsamurai@comcast.net> wrote in message
> news:VaqdnXqdIN7aZ_PZnZ2dnUVZ_vqdnZ2d@comcast.com...
>> [Well thought out, but not at all right postulates of video memory usage deleted]
>
> Anyway, this is mostly acedemic and I am going off the schematic only right
> now. It isn't worth it to drag out the references since the diagnosis is the
> same, though it now makes the color RAM itself the MOST likely suspect. Chip
> selection of the color RAM is still a high possibility. So the
> troubleshooting steps mentioned in my reply remain valid. It appears that
> the CPU has direct access to the first 1K of color RAM, but testing that
> with code would probably be meaningless because it would not really isolate
> the cause, only highlight the symptom which you already know.
>
> Scott McDonnell
Let's set the record (mostly) straight on how the standard video
modes work (this is from memory, please correct me as I err..):
1. Text from the ROM's:
Character lookup information is taken from an (approximately) 1k
memory space. The VIC fetches shape information from the Character ROM.
Color is fetched from the lower nybble of the 1k x 4 CRAM. (The upper
nybble does not exist) Background color is from a register in the VIC-II
2. Custom character sets:
Same as above, but the shape info is fetched from the 4164 DRAM's
3. Hi-Res Bitmap mode:
Pixel information is fetched from the DRAM's in an 8k matrix.
Color information is fetched from the 1k matrix which normally is the
character lookup matrix. Upper nybble is background color. Lower nybble
is background color. CRAM doesn't enter into the mix.
4. Multicoolor bitmap mode: The horizontal resolution is halved, and
color source is determined with 2 Bits Per Pixel in the same 8k matrix
as above
00 = Background color from VIC-II
01 = Color from upper/lower nybble (I forget) of text screen
10 = Color from lower/upper nybble of text screen
11 = Color from CRAM.
Most likely, it's modes (3) and (4) that the OP is having problems with-
and that points squarely at the DRAMs, IMO.
The chips themselves may not be at fault, possibly the latches that
handle /CAS and /RAS for the DRAM's. a scramble there may cause all
sorts of funkiness.
This is why I'm trying to swicth my 128 over to SRAMs.
-Urson Bear
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