Coleco Adam Capacitor Replacement Guide

Coleco drawing 41234 rev. E, the Adam's linear power supply. The four reservoir capacitors are on the left of each section.

The electrolytic capacitors of the Coleco Adam that matter most are in the linear power supply in the SmartWRITER printer, which feeds the whole system: four large reservoir capacitors, up to 15,000 µF, and the output capacitors of its four regulators. The values below are read from Coleco's own drawings: the power supply schematic (drawing 41234 revision E) and its parts list in the Technical Reference Manual, and the schematics of the printer board and the data drive's read/write and servo boards. For what a failed capacitor looks like, see Capacitor Failure Symptoms; for the rails and fault-finding, see Coleco Adam Troubleshooting Guide.

Safety

The power supply board sits in the printer next to its mains transformer. The transformer primary, the switch and the mains cord carry mains voltage, and the reservoir capacitors hold charge after the printer is unplugged. Unplug the printer, then check each reservoir capacitor with a meter before touching the board.

Before recapping

Coleco's check-out guide names no capacitor as a common fault, so find the failed section of the supply before ordering parts. Check fuses F1 (+5 V) and F3 (+12 V inductive and the 18 V line). Then disconnect the memory console and measure the outputs unloaded: the +5 V and +12 V inductive outputs have foldback current limiting, so an overload in the console can hold a rail low while the supply itself is healthy. A section with no DC across its reservoir capacitor (C2, C8, C15 or C20) has its fault on the winding, rectifier or fuse side; one with DC at the reservoir and none at the output has its fault in the regulator circuit. The step-by-step method is in the troubleshooting guide. Replace capacitors that are bulged or leaking, or that measure out of tolerance; see Capacitor Failure Symptoms.

Linear power supply

Linear power supply electrolytic capacitors (drawing 41234 rev. E and Technical Reference Manual parts list)

Ref	Value	Rating	Section	Position	Coleco part no.
C2	10,000 µF	16 V	+5 V	Reservoir after BR1	41347
C4	220 µF	35 V	+5 V	Output	41352
C6	150 µF	50 V	+12 V inductive	With CR12 and CR13 on the 14 V winding	41354
C8	15,000 µF	25 V	+12 V inductive	Reservoir after BR2	41348
C9	1,000 µF	50 V	+12 V inductive	With R11 and the 20 V zener ZR1
C12	220 µF	35 V	+12 V inductive	Output	41352
C15	3,300 µF	25 V	+12 V logic	Reservoir after CR17–CR20	41349
C17	22 µF	50 V	+12 V logic	Output	41353
C20	470 µF	16 V	−5 V	Reservoir before the 79M05	41508
C21	22 µF	50 V	−5 V	Output	41353

Values and ratings from the schematic; the parts list in the Technical Reference Manual (appendix 4.4) gives the same values and the Coleco part numbers. The part number for C9 is not legible in the available scan. C11 is not fitted: the drawing's designation table lists it as deleted.

The other capacitors on the board are ceramic discs of 0.01 µF to 0.047 µF. They do not need routine replacement.

C20 and C21 are on the −5 V rail. Fit them with the polarity shown on the board and the schematic, not by analogy with the positive rails.

Other parts of the supply

The schematic and parts list name the semiconductors and fuses that are replaced alongside the capacitors when a rail has failed:

• U1, U2, U3: µA723 regulators for +5 V, +12 V inductive and +12 V logic. U4: 79M05 for −5 V.
• Q1, Q3: 2N3055 pass transistors (+5 V and +12 V inductive). Q2, Q4: TIP31A drivers. Q6: TIP41A pass transistor (+12 V logic).
• F1, F3: 5 A slow-blow fuses (3AG), for the +5 V and +12 V inductive sections.
• ZR1: 1N4747A, 20 V 1 W zener. CR1–CR21: 1N4002 diodes.

Printer board

The printer board carries the printer's 6801 and the drivers for its motors and solenoids. Its schematic shows these polarised capacitors:

Printer board polarised capacitors (Coleco printer board schematic)

Ref	Value	Rating	Position
C4	4.7 µF	Not marked	On the + input of comparator U1B (LM339) in the reset circuit
C10	10 µF	Not marked	Supply input filter, after R34 and L1
C12	4,700 µF	25 V	Print solenoid circuit, with Q2 (TIP140)
C13	4,700 µF	25 V	Ribbon solenoid circuit, with Q3 (TIP140)
C17	22 µF	Not marked	In series with the base drive of Q2
C18	22 µF	Not marked	In series with the base drive of Q3

A further polarised capacitor, C5, sits beside R10 in the comparator circuit, but its value is cut off at the edge of the scanned sheet. Read its value, and the ratings the schematic does not give, from the parts on the board. The drawing's notes make every capacitor not otherwise marked a ceramic disc.

Data drive boards

Digital data drive polarised capacitors (drawings 41841 and 41842)

Board	Ref	Value	Rating	Rail
Read/write (41841)	C1	22 µF	16 V	+5 V input
Read/write (41841)	C2	22 µF	25 V	+12 V logic input
Servo (41842)	C20	47 µF	25 V	+12 V inductive input
Servo (41842)	C21	47 µF	12 V	+5 V input

The read/write schematic marks C1 and C2 as −10/+50 % tolerance. Both boards are drawn "used on 2404/2410". The read/write board also has two 1 µF 10 V non-polarised capacitors (C6, C7), and the servo board 1 µF tantalum capacitors (C3, C10).

Memory console

The memory console's boards are drawn on sheets 1 to 4 of the schematic set. The parts list for the Memory and I/O board in the Technical Reference Manual is not legible in the available scan, so take values for those boards from the schematic sheets or from the parts themselves.

Procedure

1. Unplug the printer and the memory console. Discharge and check the power supply reservoir capacitors.
2. Photograph the board and note the polarity of every electrolytic before removing it.
3. Replace one capacitor at a time with the same capacitance and an equal or higher voltage rating, in a size that fits the board. Axial or radial matters for the large reservoirs: check the footprint before ordering.
4. Clean the flux off and inspect the joints.
5. Before reconnecting the memory console, power the supply on its own and measure the rails against the tolerances in the troubleshooting guide.

See Recommended Tools for equipment.

Related pages

• Coleco Adam
• Coleco Adam General Maintenance
• Coleco Adam Troubleshooting Guide
• Coleco Adam Documentation
• Capacitor Failure Symptoms