Last year, I repaired an Apple PowerBook 1400CS-166 for a friend of mine, which required a recap of the mainboard, backlight board and display driver board, a replacement for the leaky original NiMH battery pack, a mainboard repair, and a new power supply.
Originally, the system seemed completely dead with no response to the power button.
Disassembly
Disassembly of the PowerBook 1400 is a fairly complex process, but it’s easy enough to do following this excellent comprehensive guide.
Mainboard Recap
The SMD aluminium electrolytic capacitors on the 1400 mainboard are a common problem – they physically leak which causes corrosion, and they don’t perform as intended which can cause all kinds of weird issues including a completely dead unit.
Aluminium electrolytic capacitors are commonly used for filtering, smoothing, and decoupling in both high- and low-voltage electronics. They are quite cheap in comparison to their solid-electrolyte counterparts (such as tantalum and polymer electrolytics), so are very common in consumer electronics.
Their useful lifetime is highly dependent on the specific application that they are used in (i.e. frequency, ripple current) and temperature, as well as the manufacturer and series of the specific component. They typically comprise aluminium windings which are coated with a liquid electrolyte, which can dry out over time (negatively affecting the performance of the capacitor, often causing them to fail dead-short), or even leak out and cause corrosion to the PCB and surrounding components.
SMD aluminium electrolytic capacitors are common, well-documented failure points in other pieces of equipment from the 1990s (i.e. Amiga 600, Amiga 1200, Apple PowerBooks, Apple Macintosh Classic / Classic II / SE / SE/30, etc), where they physically leak and cause board corrosion.
The 1400 mainboard is easy enough to recap, having only ten SMD capacitors:
You can usually buy capacitor packs for these machines from sellers such as Console5, but I just made up my own by noting the specifications of all of the electrolytic capacitors on the board, and ordering a set of high-quality known-brand parts.
In this build, I decided to use tantalum electrolytic capacitors for the smaller capacitors in the display boards and polymer aluminium electrolytic capacitors for the larger capacitors on the mainboard, both of which are equivalents to standard aluminium electrolytic capacitors – these use a solid electrolyte, meaning that they will not physically leak.
When substituting electrolytic capacitors, the capacitance needs to be the same, and the voltage rating can be the same or higher (within reason) – when you’re going through all this effort to recap something, be sure to use high-quality replacements.
For SMD capacitors, I usually remove all of them at once using a hot air rework station with kapton tape and aluminium foil to protect the surrounding areas, or by carefully twisting them off using needle-nose pliers (this technique may not be suitable if the pads are damaged, as they could delaminate from the board – and push downwards, don’t pull upwards!). The pads can then be cleaned up using new solder and either desoldering braid or a desoldering station. The board should then be thoroughly cleaned to remove any leaked electrolyte and leftover flux, using isopropyl alcohol and an ESD-safe brush.
When fitting new electrolytic capacitors, you must take care to ensure that the value, voltage rating, and orientation of the new capacitor are correct – electrolytic capacitors are polarised, so must be installed the correct way around, else they’ll get hot when powered on (and probably explode). The polarity is marked on the case: for aluminium electrolytic capacitors, the negative side is usually shown by a white stripe (for through-hole) or a black bar (for SMD); for tantalum capacitors, the positive side is usually shown by an orange or white bar (for SMD). This catches a lot of people out!
You can’t always trust the orientation markings on the PCB silkscreen (if it even has them, not all boards do), as sometimes mistakes were made in the design from the factory (take the PCB layout of the audio circuit on the Commodore CD32, for example), so care must be taken to match the orientation of the new capacitor with the original. Make sure to take lots of “before” pictures for reference, and double-check throughout.
Display Boards Recap
There are two boards in the display area which also suffer from leaky SMD aluminium electrolytic capacitors, including the backlight and display board.
The backlight board can be accessed by removing the RF shielding around it – on this unit it has only two electrolytic capacitors which I replaced with the following:
The display board can be accessed by removing the display bezel.
The display board has six electrolytic capacitors, which I replaced with the following:
- 4 x 3.3uF 50V tantalum SMD electrolytic capacitor.
- 1 x 10uF 16V tantalum SMD electrolytic capacitor.
- 1 x 33uF 10V tantalum SMD electrolytic capacitor.
PRAM Battery Rebuild
The 1400 has up to two internal PRAM battery packs, each of which is made up of two individual rechargeable cells. After a long time in storage, these were understandably dead, and due to their age I decided to replace them anyway.
I bought four replacement Panasonic VL2330 cells with pre-attached solder tabs, and soldered them together with the original flying leads – two in series with a balancing lead in the centre. I then wrapped the new packs in some electrical tape to help insulate them, and fitted them back into their original shells.
Battery Pack Rebuild
The original laptop battery pack was completely dead – I dismantled it to check the condition of the NiMH batteries inside, and unsurprisingly these were leaking.
The original is a 9.6V 4000mAh NiMH pack, comprising a Sanyo 8HR-4/3FAU (13.5cm x 7cm x 2cm) – I found a replacement pack for sale that may be suitable, however the owner decided not to go ahead with the replacement, so I gutted the original pack instead.
Mainboard Repair
With all this work performed, I tested the machine out with its original M4896 PSU, but it was still completely dead – I tested the PSU and its output voltage was insufficient, I dismantled it to inspect inside and the output side seemed to be burnt up (probably due to overload, more on this later).
I salvaged the proprietary power connector off the original PSU and fitted it to a modern 24Vdc 2A PSU, then tested the machine again – the speaker repeatedly “clicked” and the screen backlight flickered as though the unit was trying to start up but constantly restarting, probably due to the overload protection on the PSU kicking in repeatedly (this seems to be a running theme now).
I tested the unit on a current-limited benchtop supply, and this immediately current limits at 1A at 24Vdc, only providing about 5Vdc. I checked the mainboard with a thermal camera to help easily identify any shorts – the new 100uF 35V SMD electrolytic capacitors at PC1-PC5 were getting pretty hot, and the Schottky diode PD1 (marked IR3H) on the underside of the board near the battery connector was getting scorching hot.
I tested PD1 in-circuit, and it tested short-circuit; I removed it to test out-of-circuit in case it was not at fault, but it had indeed failed short-circuit, possibly due to the failing battery pack overloading the charge circuit; I replaced PD1 with a suitable 60V 3A Schottky rectifier diode (30BQ060), and the laptop now booted for the first time!
The electrolytic capacitors at PC1-PC5 which were previously hot were now cool – these were probably exposed to AC from the shorted rectifier diode. Thankfully this wasn’t for long and was only a low voltage, so I don’t think this will have caused any lasting damage.
The picture below on the right was when I installed a through-hole part for testing purposes as I didn’t have any SMD ones, I later replaced this.
I reassembled the laptop to be able to test it properly, and it booted onto its HDD!
Reassembly & Testing
Reassembling the PowerBook 1400 was just the opposite of its disassembly.
With the system reassembled, everything worked great! I’d say that this has been a very successful repair and restoration.
