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Psion Revo Battery Replacement

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Psion Revo
A Psion Revo. The two NiMH AAA cells sit under the lid nameplate.

Battery replacement for the Psion Revo, the Psion Revo Plus and the rebadged Diamond Mako. The Revo runs from two internal NiMH AAA cells soldered to a connector and sealed inside the case, where the Psion Series 5mx takes two user-replaceable AA cells.[1][2] Psion's handbook gives the Revo's cells as 650 mAh; the cells in David Savery's Revo Plus were 700 mAh.[3][2] Savery puts the job at about half an hour with the right tools.[2]

Before starting

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  • Back up the machine. Disconnecting the battery resets the Revo to factory state.[2]
  • Read the whole procedure first. There is almost no spare room inside the case.[2]
  • Desolder the battery wires from the cells; do not cut them.[1]
  • Keep the iron tip off the cell body.[1]
  • Do not damage the thermistor wrapped in with the cells. The charge controller uses the cell temperature to detect the calibration point and to cut back to trickle charge.[1][4]

Tools and parts

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Parts and tools[2][1]
Item Detail
Cells Two NiMH AAA cells with solder tags, of at least the original capacity. Higher capacity works and runs longer, but needs a longer first charge.
Chemistry NiMH only; the charging circuit is not suited to anything else.
Tools Scalpel or watchmaker's knife, small flat screwdriver, jeweller's screwdrivers, fine-tipped soldering iron
Consumables Heatshrink or tape to re-wrap the pack; hot-melt glue or silicone sealer (not superglue)
Useful Dental floss for lifting the nameplate without bending it

Cells without solder tags will not do, because the connector is soldered directly to the cells.[2]

Procedure

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Disassembly

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  1. Prise off the Psion nameplate on the lid. A scalpel used carefully avoids damage; a heavier tool or stronger glue can dent or deform it. Dental floss worked under the plate avoids bending the badge.[2]
  2. Under the nameplate are two pins in retaining slots, holding the screen casing onto the silver case top. Prise each pin up and push it towards the centre to release the case top.[2]
  3. Lift the case top to expose the battery pack, the battery connector and the IrDA/power connector board.[2]
  4. Unhook the left side of the battery bay from the main body to get clearance to lever the pack out. Do not twist the ribbon cable on the right.[2]
  5. Prise out the battery pack. Unhook the spring on the right of the bay from the silver case top, and the spring on the left if one is fitted.[2]
  6. Lever out the pin holding the silver case top to the graphite case bottom.[2]
  7. Unclip the silver case top from the graphite bottom with a small flat screwdriver, starting at the left edge where the pin came out. The right edge is held by a spike, so push the top to the right to clear it.[2]
  8. Undo the screw holding the IrDA/power/battery connector board. The battery pack and board come out together.[2]
  9. Break the glue on the battery connector and unplug the pack.[2]

Replacing the cells

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  1. Remove the plastic or tape around the cells, starting from the left. Inside are the two AAA NiMH cells and a strip of flexible circuit that serves as the temperature sensor.[2][1]
  2. Desolder the connector from the old cells, keeping the full lead length.[1]
  3. Recycle the old cells at a battery collection point, not in household waste.[2]
  4. Solder the two new cells in series, positive of one to negative of the other.[2]
  5. Solder the connector on: red wire to positive, black to negative.[2]
  6. Wrap the pack in heatshrink or tape with the temperature sensor held against the cells as before. Keep the pack as slim and short as possible; a bulky pack will not go back in.[2]

Wrap the pack as tightly as the original. A small number of early 8 MB Revos had cells that shook loose in the pack and reset the machine, and Psion's fix was to fit correctly sized cells and glue them.[4]

Refitting

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  1. Plug the pack into the board and put a small dab of hot-melt glue or silicone sealer over the connector so that it cannot work loose. Do not use superglue; hot-melt peels off when the cells next need changing.[2][1]
  2. Refit the pack and board. Do not force anything; if a bulge fouls, try rotating the pack.[2]
  3. Take care of the microswitch on the rear, which switches the Revo on and off as the case opens and closes. It breaks easily if the battery bay is forced back in.[2]
  4. Push the case top back onto the screen and refit the pins. If the pack is not seated properly the Revo will not open or close cleanly, so check that before going further.[2]
  5. Glue the nameplate back with hot-melt glue.[2]

First charge

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The battery gauge has to be recalibrated after a battery change.

  1. Perform a hard reset: open the Revo and press an unfolded paperclip into the reset holes marked 1 and 2 at the same time, then press Esc (On) twice. The Revo beeps once after a hard reset; two beeps means only a soft reset happened.[3]
  2. Charge without interruption from empty to full. Psion's first charge takes up to 6 hours. Kevin Millican recommends keeping the machine switched off during this charge and ignoring the gauge.[3][4]
  3. The red charging light goes out when the Revo moves from fast charge to trickle charge at about 85 %; charging has not finished at that point.[3]
  4. If higher-capacity cells were fitted, extend the charge in proportion.[1]

Afterwards, avoid putting the Revo on charge when it is already above about 80 %. The charger detects its calibration point from a thermal change at about 84 % of indicated capacity, and if charging starts above that point it can fail to drop to trickle charge and overcharge the cells.[4][1]

Further disassembly

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Savery's teardown continues to the screen and main board:[2]

  1. Pull out the screen hinge pins on each side of the keyboard to separate the screen from the keyboard, without twisting the ribbon cables.
  2. Prise up one corner of the keyboard and peel it off, then lever the PCB out from the front and turn it over. The speaker stays in the base.
  3. To free the screen ribbon, flip up the connector restraint; with the restraint lifted, the ribbon needs no force.
  4. Prise the screen out of its surround starting at the bottom and working up the sides. Too much pressure cracks the screen.

Savery's own machine came out of this with a dented and scratched case and a broken case microswitch. Under black tape on the screen PCB he found pads marked EL+ and EL−, but no voltage across them.[2]

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References

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  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 "Psion Revo", Wikipedia, section "Battery".
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2.19 2.20 2.21 2.22 2.23 2.24 2.25 2.26 2.27 David Savery, "Psion Revo/Diamond Mako Disassembly & Battery Replacement", R3UK, 9 August 2004.
  3. ↑ 3.0 3.1 3.2 3.3 Psion Computers PLC, Psion Revo Handbook, version 1.1, February 2000: "The battery & charging" (p. 17), "Troubleshooting" (pp. 202–203) and "Specification" (p. 206). Hosted on this wiki as File:Psion Revo Handbook (February 2000).pdf.
  4. ↑ 4.0 4.1 4.2 4.3 Kevin Millican, "Revo Battery Information", 25 May 2003.


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