> > I have a Gesswein MFM emulator from decromancer.ca; who offer an adaptor > that yields a 2nd MFM data connector. > I'll use mine in a Microvax 2000. Does anyone know how to hook it up as > two MFM drives in a Microvax 2000? > > The vendor sold a 1in high adaptor box, BA40A, with DD50 connectors to a > second cabinet (same as CPU box) for a second drive. > DEC configured both primary and secondary drives identically (drive 3, IIRC). > The Microvax 2000 Technical Manual gives the pinout from the mother board > to the MFM/floppy daughterboard, but I can't find the pinout from that > daughterboard to the cables anywhere. > > I've been looking for a BA40A, for some years now, to trace the pin layout > for a 2nd drive. Does anyone know it? > Has anyone successfully configured a single MFM emulator as two MFM drives > in a Microvax 2000? Or to an RQDX3? >
I've had two real MFM drives running with one of my VAXstation/MicroVAX 2000 machines but it is a long time since I've looked at this stuff so I'm not certain of the details. I didn't use any adapter box or cables with DD connectors. I only had the original DEC ribbon cable that connects from the VAX motherboard to one MFM drive and one RX33 floppy drive. I used this as a guide to make up a new longer cable with an extra 34 pin edge connector in parallel with the first MFM drive control connector. I ran this cable out through the hole in the bottom of the case where the cable to the adapter box was intended to run so that the added connector could be placed on an external MFM drive. I also connected a straight through 20 pin IDC to edge connector ribbon cable salvaged from a PC from the vacant 20 pin IDC connector on the VAX motherboard to the data connector on the second MFM drive, running it out through the same hole in the VAX case. IIRC I had to jumper the second MFM drive as drive 4. Presumably I should have made a twist in the cable to allow the second MFM drive to be configured as drive 3, the same as the first drive. I think the first MFM drive showed up as DUA0, the second one as DUA1 and the floppy as DUA2. I recall an incident when I tried to connect one particular second MFM drive externally and the VAX refused to power up. It seemed the overcurrent trip was operating in the power supply and the extra drive appeared to be the cause of this. I'm a bit hazy on exactly what I did to try to get around this issue, I suspect I tried powering up the VAX with the drive disconnected and connecting it after power up. Anyway, the upshot was that one or two of the conductors in the 20 pin data cable got extremely hot and the insulation on them started to smoke before I quickly switched off. I'm not sure but I think the reason was that the particular drive placed an unfused +5V on some pins on the data connector and the corresponding pins were grounded at the VAX end. Or it could be the other way around... Luckily there was no damage to anything other than the cable. Regards, Peter Coghlan.
