Casio A158W

Casio launched the A158W in 1989. Its own product page says the design has not changed since. It is a digital watch with an alarm, a stopwatch and a light, in a chrome-plated resin case on a stainless steel bracelet. The case is 8.2 mm thick. Inside is module 593. The number is stamped in a small box on the caseback. It is the same module that runs the resin-cased Casio F-91W. Casio's manual for module 593 rates it at ±30 seconds a month and about seven years on one CR2016 lithium cell. That battery figure assumes the alarm sounds for 20 seconds and the light is used for one second each day. Casio explains the low cost in plain terms. Its page credits an optimized module and a smaller total number of parts. The same manual also tells owners that pressing the buttons in the wrong order cannot damage the watch. Casio still lists the A158W today. The line now includes versions with a different color scheme and with a stainless steel mesh band. The surprising part is the second life of the module. Sensor Watch, an open-source project, makes a replacement circuit board for module 593 watches. Its documentation lists the A158W as compatible. The owner swaps the board and gets a programmable watch in the original case. The same page warns that many of these Casio models are counterfeited, and tells buyers to use a reputable seller.

Everyday timekeeping with almost no upkeep. Casio's manual quotes ±30 seconds a month and about seven years on one CR2016 cell. A thin, light watch on a metal bracelet. The case is 8.2 mm thick and the watch weighs about 46 g, according to Casio's Australian distributor. The bracelet adjusts to wrists from 145 to 205 mm. Simple daily tools. There is a daily alarm, an hourly signal and 12- or 24-hour time. The stopwatch reads to 1/100 of a second, with split and 1st-2nd place times. A base for a project. Sensor Watch lists the A158W among the watches that take its programmable replacement board. Where it falls short: the light is weak. Ben's Watch Club calls the backlight remarkably weak. Water resistance is for daily life only. Casio describes it as fine for washing up or sudden rain and gives no depth rating. It is not a swimming watch. The case is chrome-plated resin and the glass is resin, not metal and mineral glass. The calendar treats February as 28 days, so the date needs setting by hand in a leap year. The stopwatch stops counting at 59 minutes 59.99 seconds. Some owners say the folded-link bracelet pulls arm hair. Ben's Watch Club repeats the complaint but had no trouble with it.

The usual cause is a flat cell. Module 593 runs on one CR2016, rated by Casio at about seven years. iFixit's circuit board guide gives the same order of work. Fit a fresh cell first, because a low battery shows the same symptoms as a faulty board.

Press L in normal timekeeping. The light is weak even on a new cell, according to reviewers. The F-91W guide at f91w.watch, which covers the same module, notes that a dimming light is usually the first sign of a failing battery.

Check the settings before anything else. The display shows a mark when the alarm is on and another when the hourly signal is on. Casio's manual says the daily alarm sounds for 20 seconds at the set time until it is cleared, and the L button stops it.

Casio rates module 593 at ±30 seconds a month at normal temperature. Its manual suggests correcting the seconds once a month against a time signal. Drift inside that range is normal.

That is not a fault. The auto-calendar is set at 28 days for February, so a leap year needs the date set by hand.

Also not a fault. Casio's manual says the stopwatch display is limited to 59 minutes 59.99 seconds.

Turn the watch over. Sensor Watch notes that a genuine module 593 watch shows the module number in a rectangular box on the caseback. It also warns that these models are widely counterfeited.

The cell is the most common reason for a dead A158W. iFixit's guide takes out four Phillips #00 screws on the back. It lifts out the rubber gasket and the module, then opens the module's four tabs with a small flat screwdriver. The new CR2016 goes in, everything goes back, and the time is set. This is careful home work. Two owners add warnings in the comments. The module fits back only one way, with two buttons on one side and one on the other. One owner needed a reset before the whole display worked.

The A158W is rated for hand-washing and rain, and the seal depends on the rubber gasket under the caseback. The F-91W guide at f91w.watch covers the same module. It says opening the case compromises water resistance unless the gasket is replaced and the case is pressure-tested afterwards. A watchmaker can do both.

If a fresh cell does not bring the display back, the board may be damaged. iFixit says a faulty board usually shows cracks, scratches or bulges. Its replacement guide moves the battery to a new board behind the LCD and clips the battery holder back at its four corners. This is home work with a replacement part. On watch-repair forums the usual view is that a digital module dead on a new cell is broken. There is no restart button to try.

A low cell makes the light dimmer, so a new CR2016 is the first fix. Beyond that, the light is weak by design. Ben's Watch Club points readers who want a brighter light to the Casio A168W, a different model with a different module.

There is no repair for a fake. Sensor Watch warns that many module 593 Casios are counterfeited. Look for the module number 593 in a box on the caseback, and buy from a reputable seller.

Owners report that the folded links can catch arm hair. Ben's Watch Club notes the complaint but had no trouble.