Atari 825 Troubleshooting
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Fault-finding on the Atari 825 printer follows two Atari documents: the short troubleshooting table in the operator's manual, for faults an owner can correct, and the detailed troubleshooting chart in the 825 Printer Field Service Manual, which works to the subassembly and a few named chips.[1][2] Cleaning, adjustments, fuse replacement and taking the printer apart are on the Atari 825 Maintenance Guide.
The 825 runs from 115 V AC through its own transformer. Mains is present at the line cord, the fuse F1 under its plastic shield and the transformer T1. Switch off and unplug the printer before correcting any fault.[1]
First checks
[edit | edit source]| Symptom | Possible cause | Remedy |
|---|---|---|
| No power, LED not lit | Line cord disconnected; power switch off; fuse blown | Connect the cord; switch on; replace the fuse |
| Power on but the printer does not respond | Paper jam; ON-LINE/LOCAL switch at LOCAL; 850 Interface Module not connected or switched off | Clear the jam and check the ribbon before switching on again; set the switch to ON-LINE; connect the 850 or switch it on |
| Print too light | Print head too far from the paper; worn ribbon | Set the head release lever to a lower number; replace the ribbon |
| Roll or cut paper does not align or advance | Paper release lever not engaged | Move the paper release lever forward |
| Ribbon does not feed | Ribbon threaded wrongly; ribbon drive rollers not engaged | Rethread it; open and release the driven roller, then turn the drive roller clockwise |
The 825 cannot be connected to the computer directly. It needs an Atari 850 Interface Module, the CX86 printer cable between the 850's parallel port and the edge connector on the back of the printer, and the 850's own power adapter. Keep the ON-LINE/LOCAL switch at LOCAL when switching on, or the printer may print random characters.[1]
Power supply
[edit | edit source]| Supply | Source | Feeds |
|---|---|---|
| +17 V unregulated | T1 (25 V AC centre-tapped), CR5 and CR6, filter C3 (10,000 µF) | Print head solenoids and carriage motor drive; input to the regulators |
| +5 V logic | VR3, filtered by C5 to C7 | All logic; lights the power LED DS1 |
| +5 V EXT | VR1 | Signal to the host that the printer is powered |
| +12 V | VR2 | Motor drive, including the line feed stepper field |
| 24 V AC | T1, switched by the SCR Q1 and diodes CR1 to CR4 | Ribbon drive motor |
C3 charges to the peak of the rectified waveform, about +17 V before heavy loading, and is the current reservoir for the solenoids.[2] Atari gives no tolerances for these supplies. The power LED shows only that the +5 V logic supply is working. With the cover on, Atari's chart has you look for it through the paper exit slot; if it is not lit, replace F1 with a fuse of the same rating, a 1 A slow-blow type.[2][1]
The ribbon motor diodes CR1 to CR4 act as switches, not rectifiers: when the SCR Q1 conducts, they complete the 24 V AC circuit to the motor. The motor stops only when the carriage is at the left margin and the magnet on it has moved away from the Hall effect sensor S1 (UGN 3013), which turns Q2 and Q1 off. Atari's chart traces a ribbon that does not move to the motor connector J002, the motor or the logic board.[2]
Flyback board and jam protection
[edit | edit source]The flyback protection board plugs into J004 on the logic board and connects to the print head through a nine-wire flexible cable. Its silicon and zener diodes protect the solenoid drive transistors, and each solenoid has its own 2.5 A fuse (CPS part FC100502).[2] One dot missing on every character points at the head cable or the flyback board, which includes these fuses.[2]
The board also resets the printer when the carriage stalls. Operational amplifiers watch the carriage motor terminals and the solenoid current, and a capacitor is kept charged by the column sense pulses from the Hall effect sensor on the head carriage. If the pulses stop for about 250 ms while the motor or a solenoid is powered, the board pulls the processor's reset low, removing power from the motor and solenoids.[2] A printer that stops and resets after a head or paper jam is doing what it was designed to do; clear the jam before switching on again.
Detailed troubleshooting chart
[edit | edit source]| Symptom | Probable causes, in Atari's order | Remedy |
|---|---|---|
| Printer on but does nothing | Paper out switch needs adjustment; fuse F1 blown | Adjust the switch; check whether the power LED is lit, looking down through the paper exit slot, and if not, replace F1 |
| Head drags (wide smudge on paper) | Head gap wrong; head-carriage assembly | Adjust the head gap; replace the head-carriage assembly |
| Light smudge under the print line | Head gap wrong; head-carriage assembly | As above |
| Paper tears, creases or jams | Head gap wrong; head-carriage assembly | As above |
| Print too light | Head gap wrong; worn ribbon; head-carriage assembly; head release lever open or part open | Adjust the gap; replace the ribbon; replace the head-carriage; turn the release lever clockwise to the printing position |
| Left margin wanders | Logic board; mechanism assembly | Replace the faulty assembly |
| Prints too slowly | Needs cleaning and lubrication; Hall effect sensor clearance wrong; print speed wrong; logic board; head-carriage assembly; mechanism assembly | Clean and lubricate; adjust the sensor; adjust the speed; replace the faulty assembly |
| Prints erratically, missing dots | Nine-wire head ribbon cable; 8049 microprocessor; logic board; print head | Replace the faulty part |
| Same dot always missing | Head ribbon cable; flyback board | Replace the cable or the flyback board |
| Pin 9 prints too lightly | Head-carriage assembly; platen assembly | Replace the faulty assembly |
| Line feed works badly | Needs cleaning and lubrication; line feed stepper belt or pulley out of adjustment; line feed stepper motor; mechanism assembly; logic board | Clean and lubricate; adjust the belt tension or tighten the pulley; replace the faulty part |
| Carriage thumps while printing | Needs cleaning and lubrication; head-carriage assembly; moulded carriage rack; mechanism assembly | Clean and lubricate; replace the faulty part |
| Print too dense at the start of the line (overprint) | Logic board | Replace the logic board |
| No ribbon movement | Ribbon motor connector J002 unplugged; ribbon drive motor; logic board | Reconnect J002; replace the motor or the logic board |
| Erratic carriage or tractor movement | Logic board | Replace the logic board |
| Tractors will not move | Logic board; head-carriage assembly | Replace the faulty assembly |
| Tractors move backwards after 10 to 15 minutes of printing, or no print | Print head assembly; flex cable | Adjust, repair or replace the head; repair or replace the cable |
| Tractors move forward continuously | Logic board | Repair or replace the logic board |
| Ribbon does not feed properly | Ribbon twisted or loaded wrongly; drive rollers not engaged | Rethread; open and release the driven roller and turn it clockwise |
| Data sent but nothing prints | Cable between the host and the printer not connected; ON-LINE/LOCAL switch at LOCAL | Check both ends of the cable; set the switch to ON-LINE |
| Contrast varies across the line | Head gap wrong; head-carriage assembly; mechanism | Adjust the gap; replace the faulty assembly |
| Roll or cut-sheet paper does not advance | Pinch roller release lever open | Pull the lever forward to the closed position |
Atari advises cleaning and lubricating the printer before any detailed repair, because dust, chaff and old lubricant cause several of these faults.[2]
Signal waveforms
[edit | edit source]Section 8 of the field service manual gives reference waveforms at the processor. The figure labels each point with a U and an ME designator; the 825 board drawing in figure 4-3 uses the U numbers. The first set is present with or without a computer attached; the second needs Atari's T825 test program running.[2]
| Point | Signal | Pulse width | Period |
|---|---|---|---|
| U3 pin 2 | Master clock (XTAL1), 6 MHz | 1.7 µs (1.66 µs calculated) | |
| U3 pin 38 | 5 µs | 11 to 12.5 ms | |
| U3 pin 11 | ALE | 0.6 µs | 2.5 µs |
| U3 pin 9 | PSEN | 0.55 µs | 2.5 µs |
| U3 pin 8 | 1.2 µs | 130 µs | |
| U8 pin 7 (test program running) | IO/M | 80 µs | 1 ms |
| U3 pin 6 (test program running) | INT, set by the speed adjustment | 2.0 to 2.1 ms |
The speed procedure in section 4.5 of the same manual sets R25 for 1.0 to 1.1 ms between column interrupts at TP1 or U3 pin 6, and for 37 to 39 lines per minute in self-test; figure 8-1 names the control R59 and gives 2.0 to 2.1 ms. The procedure is on the maintenance guide.[2]
Replaceable parts
[edit | edit source]| Part | Centronics part number | CPS part number |
|---|---|---|
| Mechanism assembly | 63680202-5003 | FA100480 |
| Logic board (old) | 63680147-4001 | FA100481 |
| Logic board (updated) | 63680193 | FA100482 |
| Ribbon drive motor assembly | 63669271-4001 | FA100483 |
| Head/carriage assembly | 63669278-5002 | FA100485 |
| Print head assembly | 62001100-5006 | FA100486 |
| Print head assembly (updated) | 62001211-5002 | FA100487 |
| Flex ribbon cable (nine-wire) | 63680142-4001 | FA100488 |
| Flyback board | 63680172-4001 | FA100489 |
| Moulded carriage rack | 63669240-2001 | FC100501 |
| Picofuse 2.5 A | 39030030-1005 | FC100502 |
| Fuse, slow-blow 1 A (Littelfuse 313001) | 39030000-1001 | FC100503 |
| 8049 microprocessor | 63669503-4004 | FC100504 |
| 8755 EPROM | 35578755-1A52 | FC100505 |
| 8156 RAM | 35578156-1001 | FC100506 |
| 7407 driver (SN7407N) | 35474070-1900 | FC100507 |
| Head adjust cam | 63669262-2001 | FC100508 |
| Solenoid driver 2N6388 | 38263880-1900 | FC100509 |
The same table lists a 555 timer under Atari part C019748.[2] The service manual has no component-level parts list, and the capacitor values on its schematic sheets cannot be read in the Internet Archive scan.
Related pages
[edit | edit source]References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 Atari, Inc., 80-Column Printer Operator's Manual for the Atari 825 (C015506, 1980): installation p. 5; replacing the fuse pp. 32-33; troubleshooting, table 7, p. 35. Hosted here as File:Atari 825 80-Column Printer Operator's Manual C015506.pdf.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 Atari, Inc., 825 Printer Field Service Manual: theory of operation, sections 2.2.9 to 2.2.12, p. 11; cleaning, section 3.2, p. 16; detailed troubleshooting chart, table 3-1, pp. 17-20; adjustments, section 4, pp. 21-24; parts list, table 7-1, and replacement part sources, p. 51; signal waveforms, section 8 and figure 8-1, pp. 52-53. Hosted here as File:Atari 825 Printer Field Service Manual.pdf.