ST-412 Jumpers

I've read the OEM manual on Bitsacers, I've also dug out the schemaitcs in the IBM Techref. There are some differences (!), but the ones you want to change all agree. YEs. Number the pins like a 16 pin DIL IC (whcih is, after all, what it is). first bar - open 8-9 second bar - open 7-10 third bar - closed 6-11 fourth bar - open 5-12 fifth bar - closed 4-13 sixth bar - closed 3-14 seventh bar - closed 2-15 eight line -- Nonexistant 1-16 OK, now for the defintions : 1-16 : 'Multiplezed'. Shorting this enables the drive at all times, for controllers with a separate control cable to each drive. The PERQ is not like this, this must be OPEN 2-15, 3-14, 4-13 : The defition of these seems to depend on the PCB version (at least if the schematics can be beleived). They may enable diagnostic modes, etc, when open. For normal operation, leave them alone, which both from your exisitng jumper block and from the schemaitcs, would be all closed 5-12 : DS4 6-11 : DS3 7-10 : DS2 8-9 : DS1 Those 4 jumpers control the drive select (DS). Normally one is closed, all the rest are open. In yuor case, 6-11 is closed, meaning the drivce is set to DS3 (normal for a PDP11?) You want ot cut that jumper and bridge 8-9 What I'd do is get one of the new-type tiny DIP switches that's the same size as an IC package (not the old 'boxy' type), and fit that in place of the jumper block. Yop can then flip the switches to set the DS line, etc) -tony