DOM Hub Service Board (DSB) Revisions
The DOM Hubs with more than one DOR card require a common clock to be fanned out through the DOM Hub
Service Board (DSB). The card distributes a common clock, a phase coherent one-pulse-per-second time
tick, and under certain circumstances, a time string from an external source
No particular mechanical modifications have been suggested.
Internal Sync. push-button
The four-pin pin-out for the push-button switch was assigned in the schematic before a physical part was
selected for the layout. Two of the pads on the selected part comprised the support frame pads formed from
a single piece of metal. The frame shorted out the switch contacts. The Rev 0 work-around is to sever at
least one of the traces that connect the switch contacts to the frame contacts.
The Rev 1 schematic will have a revised pin assignment.
The DSB schematic indicated that a single 8-socket, ganged RJ-45 connector is used for signal output. Two
4-socket, ganged RJ-45 sockets were substituted into the layout during the layout process. Functionality
The Rev 1 schematics will be revised to indicate the alternate part selection and pin-out.
Duty Cycle accommodation
The signal processing of the one pulse per second input of the DSB accommodated the typical 20 us wide
pulse of an external source (like a GPS clock), however, a 1 Hz, 50% duty cycle clock was not adequately
accommodated. The trailing edge of the signal output from the DSB chattered, and returned to the neutral
value prematurely. The work-around for Rev 0 is to remove C40, and
move R63 into its place. The input is thereby converted from AC coupled to DC coupled.
The Rev 1 schematics will have a revised input circuit.
R66 and R68, 50 ohm input termination resistors, in the layout were 0603 size due to an error in the
footprint attribute of the original netlist. The Rev 0 workaround requires the larger parts 1210 parts to
be tacked onto one of the two pads, thomb-stone fashion, with the other end connected to the pad by a short
piece of 30AWG jumper wire.
In Rev 1, the termination resistor footprints for these parts will be corrected in the schematic, and
verified in the layout.
The original schematic and netlist identified a particular ethernet transformer which was not readily
available. The available replacement had a different footprint,. The Rev 1 schematic has been modified to
reflect the changed part.
Revisions to the DSB are not yet complete. G. Przybylski, LBNL, for IceCube