Litronix 'eats'crystals - is it me ?

[james_stan]

Hi All

If you have read any of my previous posts you will see I have been
trying to learn bits on a couple of litronix modules.

One has exposed bond wires so I guess after my ham-fisted effort at replacing the crystal it is b*ggered. Will no even show the 32KHz.

The other is stranger. On three occassions now I have replaced the crystal and it will start to work. I can 'scope the crystal and see 32 KHz. I can then short the cotnrol and set buttons to 3 Volts and
the LEDS come on and I can increment digits etc. (although I could still use a Litronix setting guide). I am powering the units using the 3v supply from a battery carrier (2 xAA) and two croc clips.

However if I leave the unit alone power disconnected and try again after a short break zippo ! On the crystal this time I could only register a flast 1.5ish Volt no 32KHz !

Is it so easy to break these crystals ?

Will they cook if the legs short with power-on ? Is it likely that the module itslef is inflicting the damage or is it simply my restrictive abilities ?

Yours frustratedly

James

[retroleds]

James:
You have a couple of things going on, possibly. First, most of the Litronix use a 32k crystal, but it was a three lead one - the third lead charged the crystal to get it "fired-up"('m using laymen's visuals here, electrical engineer types don't chew my head of f). The crystals were made by Statek Corp., their design had a larger piece of crystal(easier to handle) but required that "jump start". Your standard two lead crystals won't work, unfortunately, which is why I personally have abandoned buying Litronix items, and are selling off the few I have left.

Guy Ball(former owner of www.ledwatches.net) has a neighbor who works for Statek - I sold the man some parts for his HP calc. and he tried to help me by sending some of their more modern 32K crystals. Two lead, useless except in a very few of the very last modules Litronix made.

Regarding the soldering of crystals - if you are not using a heat sink between the solder point and the crystal, you are probably damaging them greatly. This is a few years old but a decent starting point on that topic. http://www.thedigitalwatch.com/Archives/QuickTip_002.htm

[james_stan]

Hi Ed

Thanks for the informative reply. In the modules I have I only see
two nodes for connecting the crystal, also the 'square' ones I removed only had two leads so maybe I have modules of the later type to which you refer ?

I did read a bit about sinking the heat when replacing crystals but chose to ignore it (no fool like an old fool right ?) - when I saw the things initially working I convinced myself I was right...

.. I'll try one more crystal with a heat sink attached and see how we go.

BTW during all this I did think about making up a crystal testing circuit. You need some caps (20pF) resistors (100k, 10M) and a cmnos inverter apparently. I thought if the output is connected to a couple of LEDs (one in each direction) an oscillating signal will light-up both = pass. Anyone else tried this to save transplanting dead crystals.


Cheers

james

[retroleds]

BTW during all this I did think about making up a crystal testing circuit. You need some caps (20pF) resistors (100k, 10M) and a cmnos inverter apparently. I thought if the output is connected to a couple of LEDs (one in each direction) an oscillating signal will light-up both = pass. Anyone else tried this to save transplanting dead crystals.

James, that sounds like way too much work(where did you get this idea?). A simpler solution is to buy an inexpensive $1 Chinese made LCD watch item, cut the existing crystal out and solder two small jumpers to the board(better to just leave the leads long and solder wire to wire with them lying next to each other). And there you have an easy way to test a crystal. You can also hook up new crystals and let them burn in for a few days before transplanting.

[james_stan]

James, that sounds like way too much work(where did you get this idea?).

The basic circuit is from an Electronics Text Book, adding the LEDs was sort of my idea - not sure if it would work even.

Anyhow I like your method much better.. will give it a try.

Cheers

James