Commodore 128 Alive!

hi all,am after a bit of help
my c128D has become poorly
on startup all i get is a black screen but if i hold down the commodore key while i start it up i get the light blue c64 background screen with the border but thats it, no text is shown at all
anyone got a idea as to wot the cause could be?

cheers

Hi,

I assume the 40/80 column key isn't pressed...  ;)

Does a cartridge work in 64 mode?

Check the following.
http://personalpages.tds.net/~rcarlsen/cbm/C128-IC.txt
(http://personalpages.tds.net/~rcarlsen/cbm/C128-IC.txt)

Cheers
Fotios

40/80 key isnt pressed

with my action replay plugged in it boots to the blue 64 screen with nothing on it
with my freeze frame plugged in it boots to a black screen

i have checked the psu and it's pushing out the right amount of power
i can also hear the 1571 drive click when i turn it on so it's initializing the floppy drive

My guess would be the PLA. It's what usually goes out first in a C64 and it's probably just as sensitive on the C128. My SX64 had a bad PLA and it showed the same symptoms as you get in C64 mode IIRC.

Quote from: bacon on January 18, 2011, 06:00 PMMy guess would be the PLA. It's what usually goes out first in a C64 and it's probably just as sensitive on the C128. My SX64 had a bad PLA and it showed the same symptoms as you get in C64 mode IIRC.

PLAs do not have an infinite data retention life.  Since almost any C-64 or C-128 still in existence will be close to 20 years old, or older, the PLA may be suffering from fading memory (literally).  The rated data retention life of contemporary programmable logic is 20 years, an optimistic number.  Programmable logic from the 1980s probably isn't as good.

Quote from: BigDumbDinosaur
PLAs do not have an infinite data retention life...
The rated data retention life of contemporary programmable logic is 20 years, an optimistic number.  Programmable logic from the 1980s probably isn't as good.

What ?!!  I always thought the PLAs were burned like PROMs.  They actually have a finite life span??  That's TERRIBLE... those monsters are soldered to the board, and where on Earth would you get a replacement?

I've got a working C128 and C64, they each gotta be 25+ years by now and still going.  Do you mean 20 years of continuous operation (175 k hour) ?  In that case, not much to worry about...

Edit
If I can go a bit further off topic, I wanted to mention something I noticed a few weeks ago, for the first time... really odd considering I've been using Commies for decades now  :P

Anyway, I was debugging some assembly code for MP128 and wanted a "cold start".  So naturally I turned off the computer for a few seconds and turned it back on; reloaded the program and it still had "warm start" issues.

So I turned it off again for a few seconds, turned it back on and took a peek at the RAM.  It was unaltered... at least the $1300 region where my ML code was at...

So I turned it off and counted 1 - one thousand, 2 one thousand, ... 5 one thousand.  Turned it back and took a peek at the RAM.  It was still there... a few bits here and there were corrupt, but the important thing was the checksum bytes were STILL intact.

I powered off again for 10 seconds and got total garbage when I peeked at the RAM  ;D

That just boggles my mind!  I mean the VIC refreshes 5 rows each raster so that all DRAM rows get refreshed at least every 3.5 ms... It seems there is 1000x factor of over-refresh (assuming no loss after 3.5 seconds per "experiment" noted above).

Now there are a couple of large caps in the C128 that I would think could hold a charge for a second after flipping the power switch... but for 3 or 5 seconds ???  And more importantly, the RAM needs refresh signals; even with a static charge in the capacitor, how are they getting dynamic refresh?

Thinking about it even more (because I need a diversion from taxes), I wonder if the VIC keeps sending refresh signals after you power off; hard to believe since the screen goes black almost immediately, but who knows?

The C128 sure is strange!  Somewhat related is the fact that VIC-II has no

• RESET[/o] line.  Even less related is the fact that the MMU has no
• CS[/o] line.
  
  Okay, now I'm just going WAY off topic, so I'll shut up.
  /Edit

Quote from: Hydrophilic on January 19, 2011, 02:42 PMWhat ?!!  I always thought the PLAs were burned like PROMs.  They actually have a finite life span??  That's TERRIBLE... those monsters are soldered to the board, and where on Earth would you get a replacement?

It depends on the PLA design.  The OTP types are more like a PROM, but erasable ones are not and thus can fade with age.  An altogether different type was the mask-programmed PLA, which would be a custom part and (theoretically) not subject to Alzheimer's.

QuoteI've got a working C128 and C64, they each gotta be 25+ years by now and still going.  Do you mean 20 years of continuous operation (175 k hour) ?  In that case, not much to worry about...

From what I've read, the fading issue has nothing to do with whether it's powered or not.

QuoteIf I can go a bit further off topic, I wanted to mention something I noticed a few weeks ago, for the first time... really odd considering I've been using Commies for decades now...So I turned it off again for a few seconds, turned it back on and took a peek at the RAM.  It was unaltered... at least the $1300 region where my ML code was at...

That's not uncommon with DRAM.  Although the individual capacitors don't hold a charge for very long, they can appear to retain data for a few seconds after power-off.  I've also noted this phenomenom with PCs.  I always give a system at least 30 seconds after powering off before powering on in cases where I want to be sure nothing hangs around that shouldn't.

Quote from: BigDumbDinosaur on January 20, 2011, 07:35 AMAn altogether different type was the mask-programmed PLA, which would be a custom part and (theoretically) not subject to Alzheimer's.

I thought the Commodore PLAs were mask-programmed and usually give up the ghost due to static discharge. Can't say I've studied the subject extensively, though.