Apple Silentype General Maintenance

Silentype with its lid open, showing the paper path; a paper roll and its two bearings lie in front (photo: StromBer, CC BY-SA 3.0)

Paper, mechanism and service procedures for the Apple Silentype thermal printer, from Apple's 1980 Silentype Printer Operation and Reference Manual and its Silentype Printer Technical Procedures. Apple's manual says the printer "needs no routine maintenance", so the work here is replacing paper and, when the print alignment drifts, adjusting the drive string and belt. Fault-finding is on Apple Silentype Troubleshooting Guide.

Safety

The Silentype runs from the Apple II's own supply through its interface card. Switch the Apple off before connecting or disconnecting the printer or working on it.

• The ceramic print head is brittle. It can shatter, and its edges can cut fingers.
• If the platen (the plastic bar that supports the paper) falls out, refit it square edge up. Fitted the other way, it lets the print head short out and ruins the printer.
• Do not apply power while the printer assembly is loose in its base: it can short the base to the deserializer card.

Paper

The Silentype uses only thermal (heat-sensitive) paper on a roll.

• A pink stripe along one edge means about five feet of paper are left.
• At the end of the roll the paper stops feeding, but the head keeps moving until the listing is finished. RESET stops it but may lose what is in memory.
• To load a new roll: open the dark lid, take out the empty core and pull the black bearings out of it. Unwrap the new roll, remove the adhesive strip and trim a ragged end straight. Feed the end under the roller as shown in the diagram inside the printer, turn the large knob on the right to advance it a few inches, push the bearings into the new roll with their square ends outwards, and drop them into the deepest notches either side. Close the lid with the loose end free.
• After a printer has been moved, check that the bearings are still in the deepest notches.
• Store spare rolls away from heat and light. Thermal printouts darken and become unreadable after several months; Apple suggested photocopying anything worth keeping and storing printouts somewhere cool and dark.

Opening the printer

Apple's procedure for removing the cover and base:

1. Turn the Apple off and disconnect the printer from the interface card.
2. Tip the printer on its back. Do not turn it right over, or the paper roll falls out.
3. Remove the five Torx screws round the outside of the base that hold the plastic cover, and lift off the cover.
4. Holding the chassis to the base, remove the other four screws. Apple advises removing all nine whenever you service a Silentype, since you nearly always need to get underneath.
5. Tip the printer back down. Disconnect the interface cable from J3, the rearmost connector on the deserializer card on the left, and lift the chassis out of the base.

The head cable is easily damaged. When refitting it, make sure it is fully inserted in its cable clip, with the small rubber pad in place, before the clip goes onto the print head assembly, and tape the cable to the left rail where it crosses the chassis.

Drive string and belt

The print head is carried on a Dacron cord wound round a pulley that the head motor turns through a belt.

To replace the string (about 40 inches of new cord):

1. Remove the cover and base, and turn the pulley until the head is in the middle of the platen.
2. Hold the pulley from below with pliers, loosen its screw, push the pulley towards the printer to slacken the string, and tighten it again. If the pulley is too close it binds; it must still turn freely.
3. Hold the idler from below, loosen its screw and move it towards you. Leave the screw loose for now.
4. Unwind the string from the pulley, cut it on the right of the head and tie the new string to the right-hand end of the old one.
5. Pull the old string from the left of the head until the new one has threaded through the right guide, across the front and through the left guide. Cut the knot out.
6. Pry the retainer out of the head assembly and discard the old string.
7. Thread the new string into the small holes from the outside of both sides of the head assembly, tie a loose knot and pull it straight back until the string is taut.
8. Pull the front of the string about 14 inches towards you. Starting at the bottom front of the pulley, wrap the string coming from the left guide six turns anticlockwise round the pulley. The turns must not overlap, or the alignment will suffer.
9. Pull the knot until the string is snug, refit the retainer, tie a new square knot with the string held snug, and trim the ends. The string must run between the idler and the paper.

Alignment

Align the printer after changing the string, or when the print margins are misaligned:

1. On a known-good Apple II, with the power off, fit the Silentype interface card in slot 1 and switch on.
2. Boot the Apple II Product Diagnostics disk, choose CARD TESTS and then SILENTYPE TEST, and accept the option to align the print head. The printer prints rows of capital H from margin to margin in both directions until you stop it with Y.
3. If the rows are more than one dot out to the left or right, check where the string winds round the pulley. Overlapping turns make the tension uneven; loosen the pulley and rewind the string if necessary.
4. Check the string tension: just tight enough not to slip on the pulley. For a coarse adjustment, loosen the pulley screw, move the pulley and tighten it.
5. Check the motor belt between the motor and the pulley: just tight enough not to slip. Overtightening makes the head move unevenly and wears the bearings. Loosen the two motor screws very slightly, start with a snug but not stretched belt, and move the motor a little to the right at a time, printing a pair of lines after each move, until the alignment is as good as it will go. Tighten the screws.
6. While the H's are printing, fine-tune the string tension by loosening the idler screw and moving the idler. Tighten it when the alignment is best.

Uneven left and right margins in bidirectional printing call for the Dacron cord adjustment; uneven head movement calls for the drive motor belt tension.

Fitting an EMI card to a non-EMI printer

Apple supplied only EMI-version deserializer cards for service. Fitted to an early non-EMI printer (model A2M0032, one-wire left margin switch), an EMI card (820-0020-02) prints with an uneven left margin unless it is modified:

1. Find the two solder pads provided on the card for the jumper. If the holes are filled with solder, clear them with a soldering iron and solder sucker.
2. Strip about 1/4 inch from each end of a one-inch length of 20 to 24 gauge insulated wire.
3. Push one end through one pad from the trace side and solder it; do the same at the other pad.
4. Trim any excess wire on the other side of the card.
5. Fit the card as usual. The chassis's left margin switch wire goes to post J5; J6 is not used.

When fitting any deserializer card, keep wires from being trapped behind the capacitor or under the spacers. On a non-EMI printer, the bottom screw must be tight because it is part of the ground path. The two motor plugs go back with the orange wire to the top pin.

Parts

Selected parts from Apple's parts list

Part	Apple number
Print head	970-0418
Head cable	970-0401
Dacron cord	970-0442
Head drive belt	970-0443
Cord pulley	970-0410
Paper bearing assembly	970-0406
Platen	970-0402
Head motor assembly	970-0404
Interface card control ROM	342-0039

Related pages

• Apple Silentype Troubleshooting Guide
• Apple Silentype
• Apple Silentype Documentation