25 Feb
2013
25 Feb
'13
2:15 p.m.
On Feb 25, 2013, at 4:12 PM, Ethan Dicks <ethan.dicks at gmail.com> wrote:
On Mon, Feb 25, 2013 at 3:59 PM, Cindy Croxton
Electronics Plus
<sales at elecplus.com> wrote:
I have a similar problem; I've noticed that the IRQ line is
constantly asserted, which it's not if I just pull the VIC
(of course, that could be because the boot routine is
crashing; the VIC otherwise looks like it's probably working
fine, since it emits a proper NTSC black screen with color
burst).
Is there a relatively simple test that can be done with an
analog scope (no storage) that can determine whether the
PLA is bad? Some of the outputs, at least, seem to toggle.
I'd like to narrow it down before I put down the money for
a replacement part.
- Dave
1 of the C64 powers on, but absolutely nothing
appears on the screen.
That is the most common failure mode, called "the black screen". Most
common cause is a faulty "PLA" (Programmable Logic Array). It can be
replaced with the PLA from another machine or can be burned from a
blank 82S100. Second most common cause is bad DRAM - 4164s. It's
usually the PLA.