quick update. turned the trapdoor expansion on to see if the magic is still happening.
its not.
blackscreen. on power on, the floppy sounds like it does a quarter spin but nothing else. power light is steady. no capslock flash code. no screen output at all. no floppy clicks, no nothing.
powered off, turned off the trapdoor ram module, turned back on, and all is well... either the ram expansion is faulty, or I've screwed up cutting the traces to the trapdoor slot I guess.
Hi,
It sounds like you have JP2 set correctly. For your memory expansion board, I'm not sure you even need to cut the trace on the motherboard. I think having the enable switch set to *disabled* will be equivalent.
The trace that gets cut for the Rev 5 board connects Gary pin 32 (_EXRAM) to pin 32 on the memory expansion header. You could test continuity between these two points to check whether the trace is truly cut.
_EXRAM is connected to ground to indicate that the memory expansion is present (as non-chip ram). If this pin is disconnected, it gets pulled up to 5V by the Amiga. For a 1MB chip configuration, this line must be disconnected from the expansion card, either by cutting the trace (rev5) or by cutting JP7A (rev6).
The Commodore A501 simply grounds pin 32 to indicate is presence to the Amiga. I suspect the enable/disable switch on your card grounds pin 32 when in the Enable position. You can verify this by checking continuity between pin 32 on the card and ground (pins 3/4 on the expansion, or any point along the thick trace that connects to these pins). If your switch does ground pin 32, then putting the switching in the disable position is equivalent to cutting the trace on the motherboard.
You can also check the voltage on Gary pin 32 to see that it has the correct state for 1MB chip. With the expansion installed, this pin should be a constant 5V in the 1MB chip configuration. If this pin is 0V, the expansion is present in the 512k configuration.
I don't see evidence from your picture that the enable/disable switch does anything more than connect pin 32 to ground, but I can't say completely from the picture. It looks like ground connects to the lower pin on the switch, and some signal line to the center pin. That probably goes to pin 32 on the connector, but that trace is on the bottom side of the board. Take a look at both sides of the board and see if there are any more connections to the switch besides the two traces visible on the top side.
Assuming the switch does nothing more than connect pin 32 to ground, I would leave the switch in the disable position and check voltages on the expansion board. You should see 5V between pins 10 and 20 on the M514256 RAM chips.
Robert
