Hello everybody. I'm pretty new to the MSX (and MSX2!) world, but I'm pretty familiar with other systems and Z80 architectures. I was hoping that people could guide me a bit trying to diagnose and fix this Philips 8250 I got "untested".
When I turn on the computer, it powers up, but I get no video at all (using SCART cable).
I opened it up and I seem to have 5V everywhere I checked (CPU, RAM, etc).
This is the actual board (in case there are multiple types):
I first checked activity around the Z80 and everything seemed fine (clock, addresses, refresh, M1, etc).
Then I noticed that the left column of RAM chips (102-105 I'm assuming those are the video memory from the diagram I saw) get quite hot. I can keep my finger on them, but barely. On the other hand, the right column are normal temperature.
When I check the signals on those, they look pretty odd.
This is the data bus on the RAM chips. I guess it might make sense if it's all black with some sync or something? Still a bit weird.
The address signals look even more strange to me:
They seem to be always high except for occasional spikes down? That's consistent across all the address pins.
Then I looked at /CAS. On chips 102 and 104, it looks exactly like the address memory pins. On chips 103 and 105, it looks more like a normal pulsing pattern:
/RAS was more or less the same.
Then moving on to the non-video RAM:
/CAS is always high (is this normal??)
/RAS is a normal pulsating pattern.
Addresses look fine.
Data looks a bit weird. It's not clean square signals and instead I get ramps and weird values. I don't know if it's because the bus goes to high-impedance at times and so the reading isn't really valid. I'd be curious to hear from people with experience with other similar models:
Any thoughts on what might be going on? Or something I should test next?
Thanks.
