Sinclair ZX80 / ZX81 / Z88 Forums

Oscilloscope. Also the busses.

Hmmm. Changing the 74LS05 made no differrence. The levels on the data bus are still low. But there is lots of activity on both busses, so I assume the Z80 is working. But after measuring around, it seems that no video signal is coming from the ULA. So probably the ULA is dead. Too bad. I suppose noo...

OK, thanks. So the original 15V supply should be good then. Well, I get something on the screen with the 15V, but not with the 9V, and only briefly something with the 12V.
I heard that some machines actually had a piece of plastic in place of the heatsink. Mine is metal though, so I should be good.

BTW, what is the correct PSU voltage for the Lambda. The one that came with it was 15V, which worries me. On the schematics it seems that voltages are internally regulated to 5V and 9V, but even so. I use a 12V supply instead, as it appears to me to be a safer solution?

In the meantime I've come to suspect that my issue really has more to do with the 74LS05, as it looks like the data bus lines behave weird, while the address lines look normal. Well changing the 74LS05 shoud be a cheap fix. So it's worth trying out. Requires you have desoldered an IC before though....

Signal should be over 4V peak-to-peak, and that is the case on the address bus, but on the data bus they are less than 2V. That cannot be right.

/Frank

Thanks!
Well, I guess that there is info about EPROM adaptors to be found on the web.
In the meantime I've come to suspect that my issue really has more to do with the 74LS05, as it looks like the data bus lines behave weird, while the address lines look normal.
/Frank

Hello!
New on this list, as I just acquired a Lambda 8300.
I need to replace the ROM in a Lambda 8300. I tried to download the Lambda 8300 ROM LAM10061.BIN, but the link seems to be broken. Does anyone here have the ROM binary.

Best
Frank