Atari Portfolio Capacitor Replacement Guide

This page provides a capacitor replacement guide for the Atari Portfolio palmtop computer. The Portfolio has a relatively small number of capacitors compared to desktop computers of the era, with most related to power regulation, voltage conversion, and the LCD bias supply. Capacitor failure can cause power instability, display problems, and data loss.

Overview

The Atari Portfolio's main board is a compact single-board design containing the Intel 80C88 CPU, RAM, ROM, and all support circuitry. The board uses a mix of SMD (surface-mount) and through-hole electrolytic and ceramic capacitors. The primary areas where capacitor failure causes issues are:

Power regulation — Input filtering and voltage regulation for the 5V logic supply
LCD bias generator — A small charge pump/DC-DC inverter circuit generates the negative voltage (~-15V to -20V) required to drive the LCD
Memory backup — A capacitor (or supercapacitor) that maintains RAM contents during battery changes
Decoupling — Standard ceramic decoupling capacitors near the CPU and support ICs

Disassembly for Capacitor Access

To access the main board capacitors:

Remove batteries and AC adapter
Warm the display window with a hair dryer and carefully peel it off (see Atari Portfolio General Maintenance#Display Window)
Remove the two black screws beneath the display window
Carefully separate the top case from the inner bezel — release the plastic clips gently with a spudger
Remove the silver screws securing the metal RF shield
Mark the orientation of all ribbon cables before disconnecting
Take extreme care with the power ribbon cable between the keyboard and display PCBs — this is fragile and easily damaged
The main board is now accessible for capacitor inspection and replacement

Capacitor List

The following table lists the electrolytic capacitors found on the Atari Portfolio main board. Due to PCB revision variations, exact reference designators may differ slightly between units. Always verify values against your specific board before ordering replacements.

Atari Portfolio Electrolytic Capacitor List
Ref.	Value	Voltage Rating	Type	Location / Function
C1	100 µF	10V	Electrolytic (SMD or through-hole)	Main power input filter — smooths battery/adapter supply
C2	47 µF	10V	Electrolytic (SMD)	Secondary power filter — post-regulator decoupling
C3	10 µF	16V	Electrolytic (SMD)	Voltage regulator output filter
C4	4.7 µF	25V	Electrolytic (SMD)	LCD bias charge pump — negative voltage generator input
C5	4.7 µF	25V	Electrolytic (SMD)	LCD bias charge pump — negative voltage generator output
C6	1 µF	50V	Electrolytic (SMD)	LCD bias filter capacitor
C7	0.47 F (470 mF)	5.5V	Supercapacitor (through-hole)	Memory backup — maintains RAM during battery changes (~1–2 minutes hold time)

Note: In addition to the electrolytic capacitors listed above, the board contains numerous small ceramic capacitors (typically 100 nF / 0.1 µF) for decoupling. These rarely fail but should be inspected if unexplained instability occurs.

Capacitor Functions and Failure Symptoms

Capacitor Failure Symptoms
Capacitor(s)	Function	Failure Symptom
C1, C2	Main power filtering	Unit fails to power on, intermittent resets, unstable operation. May appear to work briefly then cut out.
C3	Regulator output	Erratic behaviour, random crashes, peripherals not working correctly.
C4, C5, C6	LCD bias voltage generation	Display appears blank even though the unit is running (key clicks audible). Contrast adjustment has no effect. If measured, the LCD bias voltage (normally ~-15V to -20V) will be absent or severely reduced.
C7	Memory backup (supercapacitor)	C: drive data lost immediately upon battery removal (instead of the normal ~1–2 minute grace period). If this capacitor has failed, battery changes will always result in data loss.

Replacement Procedure

Tools Required

Temperature-controlled soldering iron (suitable for SMD work — fine tip recommended)
Solder (leaded 63/37 recommended for ease of work on vintage boards)
Flux (no-clean liquid flux)
Desoldering braid or solder sucker
Isopropyl alcohol (90%+) and brushes for cleaning
Multimeter for verification
Tweezers (anti-static)
Magnification (loupe or stereo microscope recommended for SMD components)

General Procedure

Photograph the board before starting — note the orientation and polarity markings of all capacitors
Verify polarity — electrolytic capacitors are polarised. The negative terminal is typically marked with a stripe on the capacitor body. On the PCB, look for + markings or filled/open pad indicators
Apply flux to the capacitor pads
For SMD electrolytics: heat one pad while gently levering the old capacitor away, then clean both pads with desoldering braid
For through-hole components (C7 supercapacitor): desolder both leads, clear the through-holes with desoldering braid or a solder sucker
Clean the pads with IPA
Place the new capacitor, verify polarity, and solder in place
Clean the area with IPA to remove flux residue
Inspect under magnification for solder bridges or cold joints

Replacement Component Specifications

When sourcing replacement capacitors:

Match or exceed the original voltage rating — never use a lower voltage rating
Match the capacitance value — higher capacitance is generally acceptable for filter caps but stay within ±20%
Use low-ESR electrolytic capacitors where possible — modern low-ESR aluminium or solid polymer capacitors will outperform the originals
For the supercapacitor (C7): Use a 0.47F 5.5V supercapacitor. This is available from major electronics distributors (e.g., Panasonic, KEMET). Ensure the physical size fits the board footprint
SMD capacitors should match the original footprint size — most are 1206 or slightly larger packages

LCD Bias Voltage Modification

A known community modification addresses the low battery warning timing. This involves replacing two SMT capacitors in the voltage detection circuit to extend the warning period from the stock 10–15 minutes to approximately 48+ hours. This modification was documented by Best Electronics and involves:

Replacing two capacitors in the battery voltage monitoring circuit with higher values
The exact values depend on the specific board revision
This modification is often combined with a crystal replacement to adjust clock speed

Consult the Atari Portfolio Technical Reference Guide and community resources for board-revision-specific modification details.

Post-Replacement Testing

After replacing capacitors:

Reassemble and insert fresh batteries
Verify the unit powers on and displays the DIP DOS prompt
Check LCD contrast range — adjust the contrast potentiometer and verify full range of adjustment
Test the memory backup: save a file to C:, remove batteries, wait 30 seconds, reinsert batteries — the file should still be present (verifying C7 supercapacitor function)
If using expansion modules, verify they are detected
Run the built-in applications (editor, spreadsheet, calculator) to verify stable operation