Atari 5200 Capacitor Replacement Guide

An Atari 5200 four-port motherboard

The Atari 5200 main board has a single aluminium electrolytic capacitor, C45, and four tantalum capacitors. The other capacitors are ceramic, polyester and polystyrene parts, which do not dry out the way electrolytics do. A recap of the console is therefore a small job; the parts that more often need attention are the two polystyrene capacitors in the sound oscillator and the electrolytic inside the external power pack.

Values below are from the parts list in Atari's CX5200 Field Service Manual (FD100127 Rev. 4) for the board named, unless a different source is given.

Which board do you have

5200 main boards

Board	Description
CA018087	Original four-port board; U designators
CA020108	Four-port "universal" board; A designators; + as the third character of the serial number
CA021374	Two-port board, with its own power jack; A designators

The board number is in Atari's parts lists and the identifying marks are from section 1 of the same manual.

Capacitor lists

Polarised capacitors

Electrolytic and tantalum capacitors (FD100127 section 8)

Ref	CA018087	CA020108	CA021374	Type
C45	4700 µF 25 V (C016033)	47 µF 25 V (C020121)	47 µF 25 V (C020121)	Aluminium electrolytic, radial
C41, C42, C119, C144	10 µF 20 V (C017516)	10 µF 20 V (C017516)	10 µF (C017516)	Tantalum, axial

C45 sits on the unregulated supply ahead of the regulators. The four-port boards take their power through the RF cable from the CX522 switchbox; the two-port takes it from its own jack.

Film and polystyrene capacitors

Non-ceramic capacitors (FD100127 section 8)

Ref	Value	Rating	Type	Atari P/N	Boards
C13, C14	820 pF	25 V	Polystyrene	C018621 (CA018087); C018261 auto-insertable (CA020108, CA021374)	All
C43, C44	0.22 µF	100 V	Polyester, radial	C010394	All
C19, C99 to C106	0.047 µF	100 V	Polyester, radial	C017518	CA018087, CA020108
C19, C99, C100, C105, C106	0.047 µF	100 V	Polyester, radial	C017518	CA021374

The remaining capacitors are axial ceramics from 10 pF to 0.22 µF.

The power pack

The CX521 power pack (C018187) used with the four-port consoles is a linear supply: a transformer, an MDL-5 fuse, a bridge rectifier and a 3300 µF 25 V reservoir, delivering 9.3 V DC at 1.95 A. The pack contains the mains transformer, so unplug it from the wall before opening it.

Trak-Ball

The CX53 Trak-Ball has one electrolytic on its lower board, C1, 10 µF 16 V (C014392).

The sound oscillator capacitors

C13 and C14 are the 820 pF polystyrene capacitors in the 4.5 MHz sound oscillator around Q4 and L1. Atari's checklists name them, with U7, Q4 and L1, for audio failures, and the audio chart replaces them if Q4's collector is at 0.5 V DC but there is no carrier. Console5 lists them as "styrene audio circuit caps which occasionally fail" and supplies ceramic (MLCC) replacements in its kit. Polystyrene melts easily, so heatsink each lead while soldering. After replacing them, set L1 so that the emitter of Q4 carries 4.5 MHz.

Atari's added capacitors

Two of Atari's tech tips add capacitors. Check whether they are already fitted before a recap.

• Tech Tip 14 (8 July 1983), CA018087: paddle jitter comes from ripple on the POKEY supply and a weak ground at U7 pin 1. The fix is a 10 µF tantalum across U7 pins 1 and 17, with an extra ground jumper.
• Tech Tip 13 (7 July 1983), later four-port and two-port boards: Signetics 74LS258s at A16 and A17 can corrupt RAM data. One fix is a second 390 pF capacitor in parallel with C145 and a 470 Ω resistor from C137 to R134; the other is a 74LS258 from another maker.

Procedure

See Recommended Tools for equipment and Capacitor Failure Symptoms for what a failed capacitor looks like.

1. Unplug the power pack. On a four-port console the RF cable also carries the power; disconnect it from the switchbox.
2. Remove the case and the RF shield, and photograph the board.
3. Note the polarity of C45 and of each tantalum before removing it.
4. Replace C45 with the value for your board. A higher voltage rating in the same size is acceptable; a lower one is not.
5. Replace C13 and C14 with a heatsink clip on each lead.
6. Clean off the flux and inspect the joints.

After the recap

Atari's flowcharts give these readings:

Supply checks

Test point	Four-port	Two-port
Centre of J3 (power and RF input)	10 to 12 V
Input of VR1	About 11 to 13 V	About 9 V
Input of VR2	+12 V	At least +7 V
Output of VR1 and VR2	+5 V	+5 V
Pin 3 of the RF module	+5 V	+5 V

Then run the colour-bar test and set R8, and the Pokey Adjust test and set R132, as described on the Atari 5200 General Maintenance page.

The switchbox bypass and C45

Console5's switchbox bypass for four-port consoles removes C45 and L8, adds a DC jack and a reverse-polarity diode, and fits a 47 µF capacitor in the C45 position with a 0.1 µF capacitor across the new jack. Console5 notes that the original 4700 µF can be refitted instead if its leads are extended and it is relocated. The modification is described on Atari 5200 AV Output Upgrade.

Related pages

• Atari 5200
• Atari 5200 General Maintenance
• Atari 5200 Troubleshooting Guide
• Atari 5200 AV Output Upgrade
• Atari CX5200 Field Service Manual