FPP Chamber 3 Retrofits / Improvements / Fixup Procedures

Introduction

Since the original construction of Chamber 3, we have modified and (hopefully) improved procedures somewhat. This document lists procedures and changes in procedures. Wenever the chamber 3 electronics is worked upon, any card stacks installed ``old style'' should be modified for the new style.

Removing card stacks

To remove a stack of cards, you must disconnect all wires to the chamber straws -- it is only necessary to disconnect them from the board.

* WARNING * Disconnecting wires from the straws, unless done carefully, can break the wire in the straw. DO NOT DO THIS!

For HV stacks, you should probably disconnect the test pulser cable form the rear of the boards; for readout stacks, you should disconnect the readout phone connectors and the low voltage power connectors. This may not be necessary if you are moving the stack aside instead of removing it.

When you pull the stack back from the straws, BE CAREFUL NOT TO PULL ON ANY WIRES, OR YOU MAY PULL ON A STRAW PIN AND BREAK THE WIRE IN THE STRAW.

RG finds it easiest to tilt the back end of the stack upward, to failitate removal.

Installing card stacks

Installing the readout and high voltage cards on the rear FPP chambers can be tricky. Following are a number of hints to make installation easier.

Changes in stack installation details

Several details have changed in how the card stacks are installed. If you remove / work on a stack that does not have the redone features, please redo it. The modified details include the following:

• All lower cards
  • Gas lines are cut short about 1 inch, to allow more access to the wires and front of the cards. The lines will have less tendency to push against the front of the card, which makes wire connection difficult and pushes wires off. This is usually done for the X and V layers, but not the U straws. SHOULD ONLY BE DONE BY A CAREFUL EXPERT.
• All upper cards
  • Some upper cards and arches relied on lower nuts into which screws / bolts were screwed. In most places, it was possible to widen the hole to accomodate 1/4" threaded rivets. The use of rivets eases removal / installation procedures, since the rivets are permanently mounted and cannot be lost.
• All readout cards
  • Originally, brown HV insulating tape was put under the edges of the board to prevent shorting of the edges of the ground foil to HV pins on the underside of the card. In humid air, this leads to a few hundred Mohm to ground along the glue, and microamp leakage currents. If a readout stack has this piece of tape, pull it off, clean off glue remnants with alcohol, and fold a piece of the white 5000 V insulating tape over the edge / corner of the ground foil, to prevent shorts / sparks to ground.
  • The original holes in the RF shields between boards were fairly tight, and made stack construction somewhat difficult. To ease stack reassembly, we have drilled out the rear two mounting holes slightly on almost all loose RF shields. This should be done to shields if a board stack is deassembled.
  • Having the RF shield only 1/4" above the readout board reduces air flow and cooling. Where possible, the top board in a stack should have the RF shield moved up to 1/2" spacing, or removed entirely.
• All HV cards
  • Pointy edges of wires between boards, especially the intercard HV connections, are cut short / smoothed off to prevent sparking.
• Lower readout cards
  • The ground foil is fastened under a clamp bar, held in with self tapping screws. To facilitate de- and re-installation, a v-shaped slot is cut in the middle of the foil for the center screw, and the holes in the clamp bar are drilled out to be clearance holes.
• Upper RO cards
  • Upper ground foils were originally attached under the shelf by a screw / nut and clamp plate, or between the arch and the shelf. This system was cumbersome for installation / removal, and chanced realignment of the arch. Boards could only be installed onto the arch with the arch removed from the chamber. It was replaced by folding back the foil an additional ~1/8 inch, and using tygon tubing to press the foil down to the top of the arch, making a ground contact to the top of the shelf. All ch 3 upper RO stacks were retrofitted in this manner.

Restringing a broken wire

• Check that wire is shorted to ground, and that impedance between two ends is infinite, or, at least, inconsistemt with neighbors, before starting. Pulser test failure may be for reasons other than a broken wire.
• Remove RO and HV board stacks, as needed. See above.
• Disconnect wires from the bad straw, and any adjacent straws which might be in the way for soldering. Pull gas tubes out of the bad straw gas cap, and any adjacent gas caps that may be in the way.Use tape, etc. to hole the gas tubes out of the way.
• Decap the bad straw. Small jeweler's screwdrivers can be used to break the glue bond at the base of the cap, and needlenose pliers can be used to break the glue bond to the pin. Putting one tine (?) of the pliers into the gas hole, pull on the cap. It should gradually separate at the base and come free. Push in on the pin, if you don't want to drag it out at the same time.
• Clean glue off from around the ferrule (as much as possible) before removing the pin and delrin. This makes it less likely glue chunks go into the straw. Clean more afterward.
• String the straw...
  • Set up blowing fixture and wire holder.
  • Blow wire through straw. Pull out a few feet extra.
  • Cut wire at input end. Holding wire at far end, pull blowing fixture out from over wire.
  • Use stringing tool to put delrin on wire at one end. Fasten end of wire by wrapping and stciking down preferably with double sided sticky tape.
  • Use stringing tool at other end to put wire through delrin insulator. Carefully put tensioning weight on wire and adjust wire over double frictionless pulleys so correct tension is applied.
  • Put pins over wire, into delrin, and insert delrins into ferrules. Make certain criented so wire to bottom of slot.
  • Put heat sinks on pins.
  • Solder nontenstioned end. Cut wire. Clean pin with cotton swab dipped into alcohol.
  • Solder tension end. Cut wire. Clean pin with cotton swab dipped into alcohol.
  • Check wire continuity / resistence.
  • Clean gas caps. Mix up some green glue. Put circle of glue around pin, just outside where gas cap will end up. Put circle of glue on base of cap. Mount cap on pin, push to ferrule. Give quarter turn of cap to spread glue, and put gas hole in correct (outer) orientation.
  • Put all stringing tools away, together, where you found them.
• Reattach gas tubes.
• Remount wires onto pins.
• Remount boards. See above.