2019-02-26 (Tu) GraLab Timer Repair COMPLETED

I found a lab timer at a thrift store and figured it was worth the risk to buy it for $5 and see if it worked. If nothing else, I thought it would make a nice enclosure with a timer face. When I connected it, the timer hand ran just like the second's hand on a clock except it ran counter-clockwise (anti-clockwise) as it should for a countdown timer. The button at the top could activate the internal buzzer, but the timer would not stop at 0 or buzz.

Enough background
Normal activation of this GraLab timer failed, but operation seemed reliable, so it seemed a reasonable and valuable use of time to try to repair any internal problems with the timer. According to eBay, a used working timer was a minimum of $20, and new timers were considerably more expensive. Those usually had a switched receptacle on the side for activating or deactivating an appliance while this unit only had a blank slot.

Troublesome timer

Hands from the face were taken off. The second's hand required a 3/32 hex key while the minute hand only needed a Phillips screwdriver. These tools were readily available and not any kind of security style.

3/32" hex tool

Screws holding the back in place only required a straight-blade screwdriver, and they were apparent rather than hidden under stickers. Inside, there was a motor with a gearbox, a buzzer, and a couple of switches. The switches can be seen on the front picture and control the incoming power and activate the siren which is the black box with four wires at the bottom of the enclosure. It would be easy to replace it with a relay for powering appliances. At the center are the motor and gearbox.

Inside the enclosure

The motor and gearbox were the heart and brains of the device. Both hands were reattached so their operation could be seen while the gearbox was exposed. Since the second's hand ran smoothly, the problem was probably not the motor.

Reconnected hands

Inside the gearbox were a couple of cams directly attached to the second's and minute's hands. When they were reattached, those cams could be moved to see their effects on the cam. A limit switch with a roller was affixed at the bottom of the gearbox. When the cams aligned, the switch would release and activate the buzzer. This alignment should have corresponded with the hands both being on 0 at the same time.

When the minute's hand was reattached, the movement changed noticeably from when the timer was purchased. The screw holding them to the face cylinder must have been loose which allowed the tracking to get off. It used to feel like gentle bumps whenever the minute's hand was moved, but after tightening, the movement moved something on the inside. In this case, the minute's cam was running.

Finding the grooves in the cams

Testing with the enclosure open was done and proved that the cams were once again in alignment and that the mechanism worked as expected. The gearbox was also loose so that the hands would jostle a bit which seemed like it could be intentional. It was not. Plastic grooves in the case provided a place to lock the gearbox in place. It was easy to reattach and felt sturdy. The groove needed to have some damaged plastic removed before it would accept the gearbox assembly again.

Damaged and repaired bracket

A short video, thirty-six seconds long, was shot and narrated. The second take was kept. Unfortunately, the buzzer at the last second set the upper limit for the sound, so the narration is quiet until the blast at the end. There was plenty of warning since the countdown happens exactly as you would expect.

Narrated video demonstration ***LOUD BUZZER AT THE END***

With a timer successfully restored, it seemed fitting to make some tea in my favorite mug.

Time for a celebration

First time here?

Completed projects from year 1
Completed projects from year 2
Completed projects from year 3
Completed projects from year 4
Completed projects from year 5

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