The Dreaded Single Digit of Death

[abem]

I have question about the dreaded single digit of death.

By "single digit of death", I'm referring to the case when a module illuminates only a single LED digit at a time. Usually, the digit illuminated is chosen randomly among the 4 available digits when power is applied and it's often a "0" or a "1" (probably because the startup time is 1:00), but it may also show other digits or incomplete digits.

I was formerly under the impression that when a module exhibited this problem, it was most likely just the quartz crystal that has gone bad which causes the display to no longer multiplex.

Since replacing the quartz crystal is a cheap and easy fix, I was hopeful that this was a generally fixable problem. However, I've run into two modules where changing the crystal has had no effect or has only temporarily fixed the problem.

My question is: How often is this the quartz crystal and how often is it something more insidious and unrepairable (the IC)?

-abe.

[Handy]

Hi Abe,
I have had two modules where the crystal didn't fix the fault.
Now that you have fitted new crystals, try warming the modules up.
They may well burst back to life, until they cool down again. This means the oscillator is not running because one of the two temperature compensation resistors has gone open circuit.
There is no real remedy for this apart from fitting a CMOS 32KHz oscillator circuit, see my post further down the page.
Some people don't like doing this as they feel that the oscillator will run the battery down quickly. The ones I use only consume 2 microamperes. As the original Pulsar oscillator circuit is not biased correctly, due to the open circuit resistor, the addition of an oscillator chip should not harm the original Pulsar IC. Only time will truly tell though.

Cheers,
Ian G1DRP

[retroleds]

try warming the modules up.
They may well burst back to life, until they cool down again. This means the oscillator is not running because one of the two temperature compensation resistors has gone open circuit.

I show nice shots and give resistance values for both sections here http://www.dwf.nu/viewtopic.php?t=2753& ... resistance

A resistor of the right value can be laid down against the circuit board, just north-west of the trimmer and both wires ran around it to the connection points, for a fairly "factory" look. Especially with a coat of black paint to make it blend in visually. Find a module that has been acid burned clean of the paint....amazing what you can see.

[Handy]

try warming the modules up.
They may well burst back to life, until they cool down again. This means the oscillator is not running because one of the two temperature compensation resistors has gone open circuit.

I show nice shots and give resistance values for both sections here http://www.dwf.nu/viewtopic.php?t=2753& ... resistance

A resistor of the right value can be laid down against the circuit board, just north-west of the trimmer and both wires ran around it to the connection points, for a fairly "factory" look. Especially with a coat of black paint to make it blend in visually. Find a module that has been acid burned clean of the paint....amazing what you can see.

Yes, that would be a good alternative