Atari XMM801 Capacitor Replacement Guide

Main control board XMM8-B02AM (FSM Figure 19). C1 and C2 are the two large cans at the top right.

The Atari XMM801 printer has eight aluminium electrolytic capacitors, all on the main control board, XMM8-B02AM. The parts list in Atari's XMM801 Field Service Manual (CO 70435) gives a value, voltage rating and part number for each. The interface board, the switch board and the mains filter board have no capacitors in the parts list. Two of the eight are the reservoirs of the printer's two supplies: C2 (3,300 µF) for the 19 V head and motor supply, and C1 (2,200 µF) for the 5 V logic supply.

Capacitor list

XMM801 electrolytic capacitors (FSM parts list p. 28 and Figure 18)

Ref	Value	Rating	Atari part no.	Circuit
C1	2,200 µF	16 V	C-228Z016EV	Reservoir after the D1-D4 bridge, input of the 7805 regulator IC7 (about 11 V DC)
C2	3,300 µF	35 V	C-338Z035EV	Reservoir after the bridge BD1, fed with about 23 V AC; drawn as "C22" on the circuit diagram
C3	10 µF	35 V	C-106Z035EV	Output of IC7, +5 V
C4	10 µF	35 V	C-106Z035EV	Emitter of the pass transistor T1, 19 V supply
C6	10 µF	35 V	C-106Z035EV	Line feed motor (LFM) 19 V line, after D6
C7	10 µF	50 V	C-106Z050EV	T3 stage on the carriage motor (CM) line
C8	3.3 µF	50 V (16 V on the circuit diagram)	C-335Z050EV	CPU reset circuit, with R33, R25 and D8
C24	10 µF	35 V (16 V on the circuit diagram)	C-106Z035EV	+5 V supply beside IC1 (74LS373)

The parts list gives the series code CE-04 for all of them except C8. The other capacitors on the board (C5, C9 to C23 and C25 to C30) are ceramic.

Where the parts list and the circuit diagram disagree, the parts list gives the higher rating, and a part at that rating serves for both. The circuit diagram labels the 3,300 µF reservoir C22, but C22 in the parts list is a 0.1 µF ceramic at the CPU supply pins, and the board layout marks the large can as C2.

Atari's check points put about 23 V AC into BD1 with the printer idle. The peak of 23 V AC is about 32 V, close to C2's 35 V rating, so do not fit C2 with a lower rating than the original.

Board locations

XMM8-B02AM parts layout from the field service manual (Figure 19)

On the layout, C1 and C2 sit at the top right beside the bridge BD1 and the transformer connector CON1. C3 and C4 are at the right-hand edge next to the regulator IC7 and the transistors T1 and T3. C6 and C7 are beside D6 and D7, to the right of CON3; C8 is beside D8 in the middle of the board; C24 is next to IC1 on the left, near the ROM.

Procedure

1. Unplug the printer from the mains and disconnect the SIO cable.
2. Open the case. The field service manual has no step-by-step case removal; its exploded view (p. 42) shows the platen knob (index 1-9), the upper and bottom cases and the M4 × 20 case screws (index 1-12).
3. Unplug the connectors to the main board: the transformer secondaries (CON1), the switch board (CON3), and the mechanism connectors CON4 to CON8 (print head, paper feed motor, carriage motor, home position switch and paper end sensor, carriage motor strobe sensor).
4. The parts list gives four M3 × 8 tapping screws for the main board. The Atari SIO interface board plugs onto it through a 14-pin connector on spacers.
5. Replace the capacitors one at a time, noting the polarity of each before removing it.
6. Refit the board and connectors, then check the supply voltages and run the self test as described on the Atari XMM801 Troubleshooting page.

Checks after recapping

Supply checks (FSM REF.7-0 and REF.7-1, printer idle)

Point	Expected
IC7 pin 1 (input, across C1)	About 11 V DC
IC7 pin 2 (output, across C3)	5 V ±5 %
Emitter of T1 (across C4)	About 19 V DC

Then hold LF while switching on to run the self test.

Related pages

• Atari XMM801
• Atari XMM801 Maintenance Guide
• Atari XMM801 Troubleshooting
• Atari XMM801 Documentation
• Capacitor Failure Symptoms