A500 jumpers question.

[jimbob]

Just wondering about the correct settings for jumpers JP2 and JP4 on an A500 rev6A motherboard.

When I got it, it just output a black screen. After some chip reseating. I could get a Kick 1.3 screen but with some problems. Most Disks would start to load but get a guru pretty soon, usually illegal instruction. Installing Kick 2.0 or A501 trapdoor would totally fail to boot.

Suspecting faulty memory, I eventually discovered JP2 had been cut but not connected to its other terminal. Bridged the jumper and all seems well again. I gather this is something to do with the address/type of trapdoor RAM. Seems like leaving both terminals disconnected is an error but what is the function and the way to use JP2?

JP4 is also cut but looks like maybe it was drilled out at the factory. Is this supposed to be open or closed for a PAL board?

[cpiac64]

jp2 and jp7 set fast or chip for a501

jp4 don't remember

[jimbob]

Ok so if I set JP2 the other way, an A501 will add 512k chip instead of slow. Anything else to do to get 1Mb chip. Am I correct that JP2 just cut and not reconnected is just wrong?

Not sure about JP7. According to schematic this changes the source of the Odd CIA tick signal from vsync to the expansion. I don't know what this means or what it has to do with memory addressing?

EDIT: Oh wait, the CIA tick selection is JP7B. JP7A is cut to prevent GARY from sensing external memory card, correct? Does this mean that if you wanted to install RAM in the empty motherboard sockets and have it be SLOW, you must switch JP7A to it's other connection, (ground).

[Brannigan]

I did the 1MB CHIP RAM on my rev6A motherboard not long ago. I'm looking at the motherboard now...

The original settings were (and modification in parentheses ):
JP7A: mid and lower pads connected (connection cut and left open)
JP2: mid and lower pads connected (connection cut and connected the mid and upper pads)

I also had a look at JP4 and it seems like the connection have been cut open. I didn't remember doing that so I did some research. JP4 controls PAL or NTSC; open for PAL and closed for NTSC.