Time problems LX200

[Bonzo]

I own a LX200 with a minor problem. The clock displayed in the keypad display runs 10 seconds an hour to fast. I think something is wrong with the crystals. From Meade Europe I have received a lonely-board they got left for a reasonable price so the telescope is working fine now.
But I like to know is some of you know were I can bay the 32.768 KHz crystals controlling the DS 1202 IC's used in the LX mainboard.
You may answer in German I can read it, but my writing is terrible!! Sorry.
Doe anyone of you know if it is possible to adjust the frequency of crystals. I tried capacitors but then the clock stoped.

 

[spatz1]

Hello...

Normally you should be able to buy the apropriate crystals in nearly
every electronics shop, e.g. Conrad (www.conrad.com), but it can be cheaper to
get a low-price-electronic clock and use the crystal out of it...these
32.768kHz-Crystals are used in nearly every digital or analog clock, normally such a clock
consists of a black blob, a piece of printed circuit and a silver, barrel-shaped crystal...

It is possible to tune the frequency of a crystal, but more than 1-2% is
normally not possible...you could calculate if your 10-seconds-off-by-the-hour
is in the range of 1-2%, then it could work.
More tuning normally stopps the crystal from starting to swing.

To do this, you normaly put a variable capacitor (1-5pF) in parallel to the
crystal and then check, if it is still swinging and what effect there is on the
clock...then perhaps you can tune it so that the clock is going right...but its easier to
change the crystal with a new one.

But in this case i would suppose the error to be in the circuit that controls the
crystal, because crystals normally go well or do not go at all...perhaps one
of the surrounding resitors or capacitors round the crystal is defect or
out of spec (=does not have whats written on)...but this is also heavy to check as you
would have to desolder them all to get them checked outside the circuit...

 

[Bonzo]

Hi Frank,

I never knew it could be that simple! Just demolish a old electronic clock and use the crystal! I most certainly gone try it!
Since Meade provide me with a new main-board I can do some experiments on the old board defect board and see how it goes. If I succeed it gives me a good working spare main-board.
Soldering-off the circuit components is a easy job. De crystal is controlled by the DS-1202 Clock chip and this chip is mounted on a IC-bracket
So changing out the chip could be helpful as well. The hardest job will be to find them. Meade Europe could not provide me with them and I could not find both items (crystal and IC) in the Conrad catalogue. But I will have a look on the internet
Many thanks for your reply.

Fokko