30-06-2025, 01:45 PM
Perfect timing....
I've been trying to resurrect my LBB system (along with a home brew S-100 system) for a few weeks now and we ran into the dynamic CAS timing being set by a capacitor (or spikes on the CAS being removed by the same capacitor !) - we had to increase the cap by 100pf as the new (much faster) RAM was being trigged by the logic spikes that were being created by the address decoding..... Several days later I twigged that sticking the oscilloscope probe onto the CAS line was stopping the random memory errors, as away we went
Only now I am stuck with the Floppy Disk Controller. I think the WD1691 Floppy Support logic chip is misbehaving - it's not changing the read clock frequency when switching between single and double density modes, and hence the FDC cannot get a good read of the flux transitions. But I don't what to go searching for this (relatively rare) IC unless I know it's the problem. It's a pity you don't still have an operating LBB, as it would be helpful to see some oscilloscope traces of the read clock and VCO control during normal disk operations
we should probably move this thread over to the "Non Microbee Vintage discussion" forum
OzHolmes
I've been trying to resurrect my LBB system (along with a home brew S-100 system) for a few weeks now and we ran into the dynamic CAS timing being set by a capacitor (or spikes on the CAS being removed by the same capacitor !) - we had to increase the cap by 100pf as the new (much faster) RAM was being trigged by the logic spikes that were being created by the address decoding..... Several days later I twigged that sticking the oscilloscope probe onto the CAS line was stopping the random memory errors, as away we went
Only now I am stuck with the Floppy Disk Controller. I think the WD1691 Floppy Support logic chip is misbehaving - it's not changing the read clock frequency when switching between single and double density modes, and hence the FDC cannot get a good read of the flux transitions. But I don't what to go searching for this (relatively rare) IC unless I know it's the problem. It's a pity you don't still have an operating LBB, as it would be helpful to see some oscilloscope traces of the read clock and VCO control during normal disk operations
we should probably move this thread over to the "Non Microbee Vintage discussion" forum
OzHolmes