Atari 1200XL Capacitor Replacement Guide

Atari 1200XL

This is the capacitor list and recapping procedure for the Atari 1200XL. Every value, voltage rating and part number below is from the parts list in Atari's field service manual for the machine. The hosted scan of that manual does not include the schematics, so the list gives each part's value but not its place in the circuit.

The 1200XL takes 9 V AC from an external transformer and rectifies and regulates it on the main board, so unlike the 600XL and 800XL it has a large filter capacitor and two regulators of its own. See Atari 1200XL General Maintenance#Power supply for the supply.

Visual inspection

Before removing anything, look for:

• bulging or split ends on the electrolytics;
• dried electrolyte or brown staining on the board around their leads;
• corroded or broken leads;
• heat discolouration around the regulators A1 and A2 and the bridge rectifier CR8.

A capacitor can have lost capacitance or gained ESR without any visible sign. An ESR meter finds these. See Capacitor Failure Symptoms.

Before replacing anything, measure the transformer on the AC range and the output of each regulator (see Checks after recapping); a fault in the supply shows there first. On his Atari Projects site Jason Moore reports that the original electrolytics in Atari 8-bit computers do not fail often, though some do.

Electrolytic capacitors

Atari's parts list has thirteen electrolytic capacitors on the main board, in four values. The list is for PCB/RFI shield assembly CA061074 and names no board revision, and Atari notes that "minor variations in design may be encountered depending upon the production date of the console".

Atari 1200XL electrolytic capacitors (Atari parts list, section 5)

Designators	Value	Rating	Description in the parts list	Atari part number
C39	10,000 µF	16 V	Cap. 10000uF (16V)	C060603
C7, C51, C52	47 µF	10 V	Cap. Alum Elec Axial	24-100476
C40, C41, C54, C93, C99, C102, C155	22 µF	16 V	Cap. Alum Elec Axial	C014393
C115, C162	10 µF	16 V	Cap. Alum Elect Axial	C014371

The parts list does not describe C39's construction. The 47 µF, 22 µF and 10 µF parts are axial.

Between C1 and C162 the parts list has no entry for C6, C33, C38, C43–C46, C49, C50, C53, C62, C69–C71, C92, C94, C101, C107, C108, C146 or C156–C161. Without the schematic the scan does not show whether those positions are empty on the board or simply missing from the list, so check the board before ordering.

Other capacitors

The rest of the board's capacitors are ceramics and small non-electrolytic parts. They rarely need replacing but are listed for board-level repair.

Atari 1200XL non-electrolytic capacitors (Atari parts list, section 5)

Designators	Value	Rating	Description	Atari part number
C1	68 pF	not stated	Ceramic axial	C014179-12
C2–C5, C8, C10–C12, C14–C25, C30–C32, C34, C48, C55–C59, C68, C95, C100	0.1 µF	25 V	Ceramic axial	C014181-03
C9, C98	270 pF	25 V	Type not stated	C061336-02
C13, C35, C64–C67, C72–C91, C103–C106, C109–C114, C120–C145, C147, C148, C151–C154	0.001 µF	25 V	Ceramic axial	C014181-01
C26–C29	0.047 µF	25 V	Ceramic axial	C014180-09
C36, C37, C149, C150	0.01 µF	100 V	Type not stated	C061337-01
C42, C47	0.01 µF	25 V	Ceramic axial	C014181-02
C60, C118	100 pF	25 V	Ceramic axial	C014179-19
C61	150 pF	25 V	Ceramic axial	C014179-09
C63	390 pF	25 V	Ceramic axial	C014180-10
C96, C97	820 pF	25 V	Ceramic (see tech tip 15 below)	C061336-03
C116	6800 pF	25 V	Ceramic axial	C014180-12
C117	1500 pF	25 V	Ceramic axial	C014180-15
C119	3.9 pF	25 V	Type not stated	C061336-01

Atari's changes to the capacitor list

Two of Atari's tech tips for the 1200XL change capacitors. Both apply only to machines showing the fault.

• Tech tip 15 (7 June 1983) deals with audio frequency drift. Where the sound is poor, missing, or needs constant readjustment, replace the ceramic 820 pF capacitors C96 and C97 in the audio oscillator with polystyrene 820 pF 25 V parts (Atari C018261, alternate C010821).
• Tech tip 19 (15 August 1983) deals with machines that show no picture with the Star Raiders cartridge, because the reset timing to the 6502 is wrong for that cartridge. Solder a 0.001 µF NPO 50 V capacitor (C014181-01) between pins 3 and 7 of U16.

A machine that has been through Atari service may already have these changes.

Replacement procedure

1. Unplug the transformer and wait a few minutes for the board to discharge.
2. Turn the console upside down and remove the six screws holding the bottom cover to the top cover. Lift out the bottom cover with the board and turn it right side up.
3. Remove the six screws holding the board, and lift the board and cartridge connector out of the bottom cover.
4. Remove the eleven push rivets from the shields, then separate the top and bottom shields and the fish paper, taking care not to damage the board.
5. Photograph the board and note the polarity mark of every electrolytic before removing anything. On axial parts the band marks the negative lead.
6. Desolder one part at a time, clean the holes, and fit the replacement with the same polarity. Use the same capacitance and an equal or higher voltage rating, and check that the new C39 fits under the shield.
7. Inspect every joint, then check with a meter that there is no short between +5 V and ground before applying power.
8. Reassemble in reverse: top shield upside down on the bench, board upside down on it, fish paper in the bottom shield, then the bottom shield on top, keeping the adjustment holes clear; eleven rivets, then the board into the bottom cover with six screws.

Checks after recapping

Atari specifies the supply as 9 V AC in, 31 VA, and 5 V ±5 % (1.7 A maximum) at the output of each regulator.

Power checks (Atari figures)

Test point	Expected
Transformer output, meter on AC	9 V AC
Output of regulator A1	4.75–5.25 V DC
Output of regulator A2	4.75–5.25 V DC
6502 (U21) pin 8, VCC, to pin 1 or 21, ground	+5 V

Then run the self test: press HELP while the power-on logo is on screen, with no cartridge fitted, and run the Memory, Audio Visual and Keyboard tests. If the colour or sound has shifted, VR1 (colour) and the sound adjustment can be reached through the top or bottom cover.

Related pages

• Atari 1200XL
• Atari 1200XL General Maintenance
• Atari 1200XL Troubleshooting Guide
• Capacitor Failure Symptoms
• Recommended Tools