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8bitforever
Account closed
Registered: Oct 2009
Posts: 48 |
Black (Blank) screen problem and the PLA EPROM solution
I have the black (blank) screen problem on my C64C.
Many circuits have been replaced and I'm now sure it is the PLA chip (906114-01) that is the problem.
What's your experience of the Ray Carlsen PLA Chip replacement ?
http://www.users.on.net/~clockmeister/other/C64PLA-27C512/
http://personalpages.tds.net/~rcarlsen/tdsweb/EPROMPLA/eprompla..
http://vic20.de/html/eprom_pla_8296_und_c64.html
Is it working without problems ?
What's your real experience on this ?
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ready.
Registered: Feb 2003
Posts: 441 |
what ICs have you replaced? On C64c, most commonly blank screen problem was solved by replacing RAM or CIAs. Have you checked for broken traces? |
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8bitforever
Account closed
Registered: Oct 2009
Posts: 48 |
Tried replacing 74LS258,74LS08,74LS257,74LS139 and 7805.
I have started up the machine without the CIA:s. Still the black screen with the dim vertical lines. The RAM:s do not run hot. This is an old C64C with the PLA chip that´s the most common chip to fail in a C64.
So I'm very intrested to hear about real EPROM PLA stories ...
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lemming
Registered: Oct 2009
Posts: 44 |
I've tried it (Ray Carlsen's), it works.
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8bitforever
Account closed
Registered: Oct 2009
Posts: 48 |
How many nanoseconds is your EPROM at ?
And you have found no bugs at all ? |
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lemming
Registered: Oct 2009
Posts: 44 |
150, no problems so far... It's a TMS 27C512-15JL
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8bitforever
Account closed
Registered: Oct 2009
Posts: 48 |
How long have you been testing it now ? (days)
Why didn´t you just wire it with cables, special reasons that you made a board ?
What type of C64 have you put the ERPOM-PLA in ? (C64C, or an C64) |
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lemming
Registered: Oct 2009
Posts: 44 |
Whoa, I didn't expect an examination there :D I really don't have an idea how many days I've been using it.
I made a board because it was fast to do. It's currently in one of my dozen Assy250425's.(=C64B"2")
I've got plenty of PLA:s but I just wanted to give a shot at building one of these 'coz it seemed interesting.
Now, I think you should stop fussing and give it a shot too ;-) if it somehow doesn't work for ya, then just appreciate the experience of having some fun with hardware 'modding' and then go eBay-hunting for an original PLA or something :).
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Digger
Registered: Mar 2005
Posts: 437 |
You can also try this one as well. I got one, it's cheap and works out of the box :)
http://www.manosoft.it/?p=14&lang=en |
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8bitforever
Account closed
Registered: Oct 2009
Posts: 48 |
Lemming, thanks for the information.
Digger, how long have you been testing it now ? (how many days)
Digger, have you noticed any bugs ? (manosoft says that the compatibility is 99%)
Digger, what type of C64 have you put the ERPOM-PLA in ? (C64C, or an C64) |
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Sabbi
Registered: Jan 2002
Posts: 8 |
I could not resist to upload a small Video to YouTube:
http://www.youtube.com/watch?v=OHevwgKo9YI
This shows my C64 with an Eprom-PLA (M27C512-15XFI) - notice the interesting color-effects.
The same Eprom works fine in another C64 (same Assy 250407), so it's a bit random what you get..
For a serious (demo-)machine, try to get an original PLA. |
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8bitforever
Account closed
Registered: Oct 2009
Posts: 48 |
Thanks for the video, very informative !
That was very interesting information that Andropolis would work with a 150ns EPROM PLA on Assy 250407.
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Quote: I could not resist to upload a small Video to YouTube:
http://www.youtube.com/watch?v=OHevwgKo9YI
This shows my C64 with an Eprom-PLA (M27C512-15XFI) - notice the interesting color-effects.
The same Eprom works fine in another C64 (same Assy 250407), so it's a bit random what you get..
For a serious (demo-)machine, try to get an original PLA.
It obviously have problems coping with the color ram fetches after about 20 chars on each line. Some vic banks more prone to error it seems aswell. Not sure this is about the speed of the chip, looks more like a logic error in the truth table to me. |
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ready.
Registered: Feb 2003
Posts: 441 |
the problem with EPROMs used as PLAs is that EPROMs are not true logic. There's no error in the truth table logic. EPROMs can garantee their outputs according to the truth table implemented only after a settling time, not in between. This is ok when an EPROM is used as a ROM, in a bus system where you have proper delays after which data is considered valid. But EPROMs cannot garantee the intermediate state and some outputs may flicker.
While a true logic chip garantees the outputs even during transitions. If an EPROM can work as a true logic is just a matter of luck.
I suggest yuo check this:
http://www.jschoenfeld.com/products/SuperPLA_e.htm
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Sabbi
Registered: Jan 2002
Posts: 8 |
Quoting JackAsserlooks more like a logic error in the truth table to me.
No logic error - same Eprom in another C64 (same assy) works fine. I also got different Results with other Eproms (also with same Brand/Type). I've ended my Eprom-PLA-Experiments with the conclusion that everything is just random, and that some machines seem more error-tolerant than others.
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Quote: Quoting JackAsserlooks more like a logic error in the truth table to me.
No logic error - same Eprom in another C64 (same assy) works fine. I also got different Results with other Eproms (also with same Brand/Type). I've ended my Eprom-PLA-Experiments with the conclusion that everything is just random, and that some machines seem more error-tolerant than others.
I think Ready's explanation says it all. |
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8bitforever
Account closed
Registered: Oct 2009
Posts: 48 |
Ok, so this is the conclusion:
The best solution is probably the none EPROM based SuperPLA (true logic).
http://www.retro-donald.de/pages/superpla-multi.php
But the EPROM solution at the right speed can be close to perfect in some C64:s.
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