Atari 810 Capacitor Replacement Guide

The original Atari 810 has nine aluminium electrolytic capacitors: eight on the rear board, which holds the power supply and the motor circuits, and one on the side board. Atari's Atari 810 Disk Drive Field Service Manual (FS015854 Rev. 1) gives the value and voltage rating of each in its parts lists, and the rear board silkscreen in its appendix shows where they sit.^[1] Sams Computerfacts CD9 has a schematic of the same two-board design with the DC voltage on each rail.^[2]

Drives built from February 1982 use the "810 Analog" design, with a Power Supply Board in place of the rear board and an Analog Board above the mechanism.^[3] Neither FS015854 nor Sams CD9 covers those boards; Atari's later field service manual, FD100003, does.^[3] Read the values off the capacitors of an Analog drive before ordering parts.

Signs of failure

No +5 V at pin 3 of A108, no +12 V at the collector of Q113, or no -5 V at the anode of CR107. Sams lists these as the power supply checks.^[2]
A spindle speed that drifts or will not hold; Atari's troubleshooting guide points to the drive motor circuit on the rear board among other causes.^[1]
Bulged, leaking or crusted capacitors, especially the three 4,700 µF filters on the rear board.

See Capacitor Failure Symptoms for general signs.

Capacitor list

**Atari 810 electrolytic capacitors, original two-board design**
Ref	Board	Value	Rating	Atari part	Where it sits (Sams schematic)	Notes
C146	Rear	4,700 µF	25 V	C014780	Bridge output, the 11.2 V rail feeding the 7805 (A108)
C148	Rear	4,700 µF	25 V	C014780	Output of the +12 V doubler, input of Q113	Sams shows 25.1 V here
C149	Rear	4,700 µF	25 V	C014780	+12 V doubler, with CR115 and CR116
C150	Rear	470 µF	16 V	C014368	-5 V doubler output	Numbered C153A on the Sams schematic; see below
C151	Rear	470 µF	16 V	C014368	-5 V doubler, with CR117 and CR118
C160	Rear	10 µF	16 V	C014392	+5 V output of A108
C143	Rear	10 µF	16 V	C014392	Input of the motor drive array A107
C142	Rear	47 µF	16 V	C015505	Drive motor circuit, at A107 and Q112	Parts list gives the part without a reference; the silkscreen marks C142 as 47 µF
C132	Side	4.7 µF	35 V	C014369	Power-up reset circuit, with R127 and Q110

Values, ratings and Atari part numbers are from the FS015854 parts lists; positions are from the rear board silkscreen and the Sams schematic.^[1]^[2] Atari's tolerances are +50/-10 % for the rear board electrolytics and +75/-10 % for C132.^[1] The parts list prints the 470 µF line as "C150, 1" because the text runs off the page; the silkscreen shows both C150 and C151 as 470 µF.^[1]

Sams shows 25.1 V at the input of Q113 (J105 pin 3), the node that C148 filters, which is at the 25 V rating Atari specifies for that position.^[2]^[1] Fit a 35 V part at C148 if one of the same capacitance fits the board.

The rear board's other larger capacitors, C152 (0.47 µF 100 V) and C145 and C158 (0.22 µF), are Mylar film types, not electrolytics.^[1]

Atari's list has two 470 µF capacitors, C150 and C151. The Sams schematic has C151 and a 470 µF C153A on the -5 V doubler output and no C150, so C153A appears to be the same part under another number.^[1]^[2]

Procedure

Unplug the adaptor and the I/O cables.
Open the drive and remove the common baseplate, the side board and the rear board as described in the maintenance guide.^[1]
Replace the capacitors one at a time, matching polarity to the board markings and noting the orientation of each before removing it.
Refit the boards. The harness plugs are not polarised, so check each one against your notes before switching on.^[1]

A108 and Q113 are mounted on the common baseplate, which is their heatsink. If either is removed, refit Q113's insulating plate and coat both devices with heat transfer compound.^[1]

Checks after recapping

**Voltages to check (Sams CD9)**
Point	Expected
Adaptor output plug	10.9 V AC
Cathode of CR111	12.0 V
A108 input	11.2 V
A108 pin 3 (+5 V)	5.0 V
Collector of Q113 (+12 V)	12 V
Anode of CR107 (-5 V)	-5 V

The figures are Sams' measurements on a working drive.^[2] Then run Atari's floppy quick-check and check the spindle speed, as on the Atari 810 Maintenance Guide.^[1]

Related pages

References

↑ ^1.00 ^1.01 ^1.02 ^1.03 ^1.04 ^1.05 ^1.06 ^1.07 ^1.08 ^1.09 ^1.10 ^1.11 Atari, Inc., Atari 810 Disk Drive Field Service Manual (FS015854, Rev. 1, July 1980): power supply p. 2-20; disassembly pp. 6-3 to 6-13; side board parts list p. 8-6 (CA014162 Rev. 10); rear board parts list pp. 8-8 and 8-9 (CA014161 Rev. 12); rear board silkscreen CA014161 Rev. B, appendix E. Hosted here as File:Atari 810 Disk Drive Field Service Manual FS015854 Rev 1.pdf.
↑ ^2.0 ^2.1 ^2.2 ^2.3 ^2.4 ^2.5 Howard W. Sams & Co., Computerfacts CD9, Atari Model 810 (June 1986): schematic with voltages pp. 2-3; troubleshooting p. 12. Hosted here as File:Sams Computerfacts CD9 Atari 810 Disk Drive.pdf.
↑ ^3.0 ^3.1 Michael D. Current (ed.), Atari 8-Bit Computers: Frequently Asked Questions, comp.sys.atari.8bit FAQ, last modified 2 August 2026, section 3.2.1. mcurrent.name. Community reference.

[fsm-1] 1.00 ^1.01 ^1.02 ^1.03 ^1.04 ^1.05 ^1.06 ^1.07 ^1.08 ^1.09 ^1.10 ^1.11 Atari, Inc., Atari 810 Disk Drive Field Service Manual (FS015854, Rev. 1, July 1980): power supply p. 2-20; disassembly pp. 6-3 to 6-13; side board parts list p. 8-6 (CA014162 Rev. 10); rear board parts list pp. 8-8 and 8-9 (CA014161 Rev. 12); rear board silkscreen CA014161 Rev. B, appendix E. Hosted here as File:Atari 810 Disk Drive Field Service Manual FS015854 Rev 1.pdf.

[sams-2] 2.0 ^2.1 ^2.2 ^2.3 ^2.4 ^2.5 Howard W. Sams & Co., Computerfacts CD9, Atari Model 810 (June 1986): schematic with voltages pp. 2-3; troubleshooting p. 12. Hosted here as File:Sams Computerfacts CD9 Atari 810 Disk Drive.pdf.

[faq-3] 3.0 ^3.1 Michael D. Current (ed.), Atari 8-Bit Computers: Frequently Asked Questions, comp.sys.atari.8bit FAQ, last modified 2 August 2026, section 3.2.1. mcurrent.name. Community reference.

[1]

[2]

[3]