Atari Portfolio Capacitor Replacement Guide

Main board of an Atari Portfolio HPC-004, C103911-001 Rev A. The 60-pin expansion connector (J3) is at the left, the memory-card connector (J4) at the right. Photo: Raimond Spekking, CC BY-SA 4.0.

The Atari Portfolio runs from three AA cells stepped up to 5 V, and keeps its internal RAM disk alive during a battery change with a capacitor. Atari's Portfolio Technical Reference Guide describes the supply lines, their voltages and current limits, and the memory-backup arrangement, but gives no component values. A recap therefore starts by reading the values off the board.

What is on the board

The main board in Raimond Spekking's photograph of an HPC-004 is marked C103911-001 Rev A. Beside the ribbon cable to the display it shows the step-up regulator circuit: an 8-pin 34063 switching regulator at U16, a moulded surface-mount capacitor marked "68" and "6V", and a small electrolytic rated 85 °C lying flat on the board. Most of the other capacitors on the board are small surface-mount parts. Ceramic capacitors do not dry out and are not part of a recap; replacing them at random risks the pads for no benefit.

How the Portfolio is powered

Portfolio supply lines

Line	What it is	Documented behaviour
Main supply	Three AA cells, stepped up to 5 V by a switching regulator that can be switched off	The cells sit well below the logic rail
VEXT	The external supply voltage, connected directly to the external jack socket	Available on the expansion bus; peripherals may use it
Initial source	Whichever of the cells or the external supply is at the higher voltage	The Portfolio runs from the higher of the two
5VS	Output of the five-volt regulator	5 V during STANDBY and RUN, floats low at other times. Rated to supply 40 mA at 5 V ±5 % to a peripheral
VCC (card)	Follows 5VS	Exists so that inserting or removing a memory card does not put spikes on 5VS
VRAM	Supply to the system RAM	4.5 V in STANDBY and RUN; initial source minus 0.5 V in OFF mode; the voltage across a capacitor in NO POWER mode
BATD	Battery detection	Goes low when the cells are removed

The four power modes are NO POWER (no initial source connected, for example during a battery change), OFF (custom chip and RAM powered directly from the initial source), STANDBY (whole system on the 5 V regulator, processor clock halted) and RUN.

Memory backup

Two separate arrangements keep data, and they are easily confused.

• The Portfolio itself. Atari states that when an initial source has been supplied and then removed, "the system RAM will be backed up by an internal capacitor", and that during NO POWER mode the voltage on VRAM decays. This capacitor decides whether drive C: survives a battery change. Atari gives neither its value nor a hold time.
• The memory cards. The RAM cards are static RAM, and each card has its own lithium back-up cell, which Atari says keeps the card's data out of a Portfolio "for a year or more". atari-computermuseum.de gives the cell in Atari's cards as a CR2016. A card that loses its data whenever it is removed has a flat cell in the card, which is not a fault in the computer.

To test the machine's own backup, save a file to C:, remove the cells, wait, refit them and check whether the file survived. If the data is lost at once, the backup capacitor is the suspect, but measure VRAM before replacing anything, since a decaying VRAM is the documented behaviour. During NO POWER mode no current should be drawn from VRAM, or the system RAM can be corrupted, and pressing the cold reset switch pulls VRAM to ground through a small resistor.

The display

The display is a 240 × 64 super-twist LCD driven by a graphics LCD controller with its own screen RAM and character ROM. Contrast is set in software, through a control register. A display that is blank while the keys still click is not necessarily a hardware fault: try the contrast keys and a cold reset first. Atari publishes no LCD bias voltage; if the bias circuit is suspected, compare readings with a working machine.

Access

Disassembly is covered on Atari Portfolio General Maintenance. Two points cause lasting damage if missed: the display window is glued and has to be warmed and peeled before the screws beneath it can be reached, and the ribbon cable between the keyboard and display halves is fragile, so note its orientation and support it; do not pull on it.

Working on the board

1. Photograph the board before removing anything, close enough to read the marking on every electrolytic.
2. Write down the location, value, voltage, package and polarity of each part as you go.
3. Replace one part at a time. Match the capacitance and package, and match or exceed the voltage rating; there is very little clearance over the board.
4. Clean the pads and check for corrosion under each part; leaked electrolyte attacks traces before it shows from above.
5. Inspect under magnification and remove the flux.

See Capacitor Failure Symptoms and Recommended Tools.

Testing afterwards

1. Check for shorts between the supply lines and ground before fitting cells.
2. Fit fresh cells and confirm the machine reaches the DOS prompt.
3. Confirm the contrast adjusts through its full range.
4. Confirm 5VS is at 5 V ±5 % with the machine running.
5. Confirm VRAM is about 4.5 V in RUN.
6. Test the memory backup as described above.
7. Confirm any expansion peripheral is still detected.

Related pages

• Atari Portfolio
• Atari Portfolio General Maintenance
• Atari Portfolio Troubleshooting Guide
• Atari Portfolio Technical Reference Guide
• Capacitor Failure Symptoms
• Recommended Tools