Atari 825 Maintenance Guide

Head gap adjustment on the 825 print mechanism, from figure 4-1 of the field service manual

The Atari 825 printer needs regular cleaning and oiling of its carriage shafts and paper roller bushings, a ribbon change from time to time, and three mechanical and electrical adjustments when print quality or speed drifts. Atari's operator's manual gives the owner's routine, and the 825 Printer Field Service Manual adds the full cleaning procedure and the adjustments. Faults are covered in the Atari 825 Troubleshooting guide.

Safety

The 825 has its own mains power supply. Switch the power off and unplug the line cord before cleaning, lubricating or opening the printer. The print speed adjustment is the only procedure done with the power on and the covers off; Atari warns of injury from the moving parts and from hazardous voltages inside the printer.

Keep the printer level when moving it or lifting the body cover. The ribbon sits loose in its tray and spills out if the printer is tipped.

Routine cleaning and lubrication

Atari 825 cleaning, inspection and lubrication (operator's manual table 6)

Item	When	What to do
Outside of the printer	As required	Mild detergent on a clean, soft, lint-free cloth
Interior	Each ribbon change	Inspect and remove any foreign objects
Print head and carriage	Each ribbon change	Remove the ribbon and brush dust from the head, ribbon path and carriage with a soft-bristle brush
Ink on the print head	Each ribbon change	Gently wipe dried ink from the front of the head with a clean, soft, lint-free cloth
General cleaning	Every 6 months	Clean as above, clean the platen with mild detergent and water, and vacuum the interior with a soft brush attachment
Carriage guide shafts	Every 6 months	Oil and wipe the shafts (below)
Paper drive roller and end plate bushings	Every 6 months	Clean the roller and bushings, then oil the bushings (below)

Atari notes that the interval depends on the environment, the amount of use and the type of paper.

Carriage shafts

1. Move the print head to the left side of the printer.
2. Put a few drops of light machine oil on a clean, lint-free cloth. Atari names Shell Tellus No. 27 light DTE or Anderol 365 SAE 10-30.
3. Wipe the carriage guide shafts with the cloth to lift any residue.
4. Move the head to the right side and wipe the left-hand part of the shafts.

Paper roller bushings

1. Clean the paper drive roller and the end plate bushings with a lint-free cloth.
2. Put one drop of light oil on each end plate bushing.
3. Turn the paper roller with the thumbwheels so that the oil runs into the bushings.

Service cleaning

The field service manual's procedure goes further, and Atari recommends it before any detailed repair, because dust, ribbon and paper chaff, residue and poor lubrication cause faults of their own.

1. Remove the cover assemblies.
2. Look inside for loose wires, connectors and hardware, chafed cables, and worn or damaged parts.
3. Remove the mechanism assembly (see below) and set it aside.
4. Brush paper and dust residue from the base and the circuit board with a soft brush.
5. Brush the print head and carriage, and wipe dried ink from the front of the head.
6. Clean the rest of the mechanism with a lint-free cloth moistened with Freon, paying particular attention to the carriage shafts and the paper roller end plate bushings.
7. Oil the carriage shafts and the end plate bushings as above.
8. Reassemble the printer and clean the outside with mild detergent.

Changing the ribbon

The ribbon is a continuous loop packed in a Centronics Zip-Pack, Atari order number CA016087.

1. Switch off, unplug the line cord and set the ON-LINE/LOCAL switch to LOCAL.
2. Lift the printer cover off from the back.
3. Move the head release lever to the LOAD position to back the head away from the platen.
4. Push the spring-loaded driven roller away from the drive roller with the plastic lever supplied, take the old ribbon out from between the rollers and unthread it.
5. Peel the film off the new Zip-Pack and put it in the ribbon tray close to the drive rollers.
6. Thread the ribbon as shown in figure 10 of the operator's manual, with one twist on the left side to make a Möbius loop. Do not twist it on the right side. Hold the ribbon tensioner arm open on the right and thread the ribbon past it.
7. Press the plastic strip down through the hole in the shell and pull the wrapper tab to remove the wrapper, then discard the wrapper, shell and strip.
8. Turn the drive roller clockwise to take up the slack.
9. Reload paper, set the head release lever to print position 1, 2 or 3, and refit the cover.

Adjustments

All three adjustments are made with the cover assemblies off. Make an adjustment after replacing a part that affects it. The tools are flat and No. 1 Phillips screwdrivers, 1/4 in and 5/8 in nut drivers, a 3/8 in ignition wrench, 2 mm and 0.050 in Allen keys, an ohmmeter, and 0.004, 0.005 and 0.014 in feeler gauges.

Print head gap

A wrong gap shows as the head dragging (a wide smudge), a light smudge under the line, paper tears or jams, light print, or contrast that varies across the line.

1. Remove the covers and lift the mechanism assembly out of the base.
2. Move the print head to the centre of the mechanism, handling the carriage by the sturdy casting above the carriage rack.
3. Set the print head release lever to position 3 and put a 0.014 in feeler gauge between the nose of the print head and the platen.
4. Loosen the set screw on the left side of the head carriage with a 2 mm Allen key.
5. Turn the cam bushing adjusting nut under the left side of the head carriage with a 3/8 in wrench until the gauge slips easily between the head nose and the platen. Keep the release lever at position 3 throughout.
6. Tighten the set screw.

Hall effect sensor clearance

The Hall effect sensor on the head carriage produces the column sense pulses from a magnetic rotor. A wrong clearance is one of Atari's causes for slow printing.

1. Remove the covers and the mechanism assembly.
2. Loosen the sensor mounting screw with a No. 1 Phillips screwdriver.
3. Put a 0.005 in feeler gauge between the sensor and the rotor and move the sensor against it until the gauge moves with slight friction. Tighten the screw.
4. Check that a 0.004 in gauge fits loosely in the gap.
5. Move the carriage by hand and watch the rotor. It must turn without touching the sensor.

Print speed

Part of the logic board with R25 and TP1, from figure 4-3 of the field service manual

This adjustment is made with power on and the covers off.

1. Remove the covers and set the printer up for its self-test.
2. Switch on and check that the power LED lights.
3. Set the ON-LINE/LOCAL switch to ON-LINE. The head moves to the left margin, then to the right margin and back, with a line feed each time it reverses at the right. This continues until the printer is switched off or set to LOCAL.
4. Count how many times a minute the head travels from left to right. The correct rate is 37 to 39 lines per minute.
5. Adjust potentiometer R25 until the rate is right.

With an oscilloscope, monitor the column interrupts at TP1 or pin 6 of U3 and set R25 for 1.0 to 1.1 ms between pulses with the carriage moving forward. The waveform figure at the back of the same manual labels the speed control on that signal R59 and gives the pulse period as 2.0 to 2.1 ms, measured with Atari's T825 test program running. Check which potentiometer your board has before turning anything. For setting up the self-test the field service manual refers to paragraph 5.5 of the operator's manual, which is not in Atari's 825 operator's manual.

Taking it apart

Cover assemblies

Lift the printer cover off from the back. The body cover is held by five Phillips screws: remove them, raise the body cover far enough to reach under its front, unplug the ribbon drive motor cable from the circuit board and set the cover down, keeping it level so that the ribbon stays in its tray.

Mechanism assembly

1. Switch off, unplug and remove the top and body covers.
2. Move the carriage to the far right so that you can reach J003. Unplug the stepping motor connector from J003 while pressing the board down beside the connector with the other hand. Pull on the connector body, not the wires.
3. Unplug the ribbon cable from the flyback board connector in the middle of the circuit board, and unplug the single-wire connector J005.
4. Pull out slightly on the retaining tabs on each side and lift the mechanism out of the base.

Logic board

With the covers and the mechanism off, remove the Phillips screw at the left front corner of the board and the two screws at the transformer, keeping the transformer heat shield and the plastic high-voltage shield over the fuse. Slide the board forwards to free its rear edge, lift the rear edge, and pull the board out of the base, freeing the line cord strain relief. Take care of the switches that pass through the front panel. On refitting, make sure the strain relief is seated at the back of the base.

Fuse

The line fuse F1 is a 1 A slow-blow cartridge fuse, 1/4 in by 1 1/4 in, on the right front corner of the logic board under a clear plastic high-voltage shield. Atari's spare is Littelfuse 313001.

1. Switch off, unplug and remove the printer cover and the ribbon.
2. Lift the body cover as above.
3. Loosen the Phillips screw on the right side of the transformer and remove the high-voltage shield.
4. Replace the fuse with one of the same rating.
5. Refit the shield with its slotted part under the flat washer, tighten the screw, reconnect the ribbon drive motor cable, refit the body cover, rethread the ribbon and refit the cover.

Auto line feed

The printer adds a line feed to each carriage return. Removing resistor R11 from the logic board disables this, but Atari advises against it with a 400 or 800, which then has no way to make a line feed except by program.

Related pages

• Atari 825
• Atari 825 Troubleshooting
• Atari 825 Documentation
• Recommended Tools