Fitting a ltc 1799 precision oscillator...

Dj Task Manager · May 31, 2009, 12:40:55 PM

Ive a ltc 1799 chip and im going to try and do the oscilator crystal replacement jobbie on my amstrad ckx100. Looking at the instructions on how to wire it up on the getlofi website the two diagrams seem to be in opposition with each other. one is suggesting wiring it up one way and the other is sort of the mirror image (left to right swap of where to wire everything if you follow...) as if one refers to the chip one way up and the other the other way up.

here is the page with the diagrams: http://www.getlofi.com/?page_id=1446

I hope this makes sense! I fear I havent managed to articulate myself very well.
If anyone knows the correct way round to wire one of these little fellas up i would be very grateful for any info.

Cheers

DJ Task Manager

Gordonjcp · May 31, 2009, 01:20:14 PM

One will be looking at the track side of the board, one will be looking at the component side and seeing the tracks like an X-ray.

the_zombiest · May 31, 2009, 07:30:35 PM

Did you get the ltc1799 from getlofi?
Is it the same revision as illustrated?
I've used the 1st revision boards before but not what they have pictured.
I'd say try it as pictured in the top diagram. Maybe they soldered the chip upside down.

LoneStar81 · May 31, 2009, 11:36:16 PM

Everyone looking for SMD adaptor boards for the LTC1799, look:

http://tinyurl.com/nm5a7h

Everyone with a bit of soldering experience should be able to fit the chip on these.
The chips themselves are about 2.95 Euro or so at my usual local suppliers.

And thanks to whoever it was who made me stumble upon it! I fit one into a Korg DDD-5,
couldn't be any simpler!

Dj Task Manager · June 01, 2009, 10:10:03 AM

i got the chip off of e-bay, its on a little adaptor board thing similar to that mention in the previous post but with pins coming down off it.

So do we recon the getlofi image is with the chip the right way up and diagram headed 'basic connections' is viewing it from trackside?

this seems a bit silly and cautious but i dont want to risk destroying it wiring it up wrong

cheers yall

Gordonjcp · June 01, 2009, 10:46:37 AM

Well, pin 1 is marked and you have the circuit diagram. If you don't have the datasheet, it's easily available on the 'net. Sit down and draw the circuit and board layout yourself before you start.

Dj Task Manager · June 01, 2009, 12:27:48 PM

awesome, i hadnt noticed that pin1 was labled

thanks g-slice

Dj Task Manager · June 01, 2009, 02:10:07 PM

one last thing...

i have a 0.1uf cap to go between pins 1 and 2 (looking at diagram headed 'basic conections'), it is axial, so does the long leg want to go to point 1 or 2?

Sorry for all my noob questions!

Mike

Gordonjcp · June 01, 2009, 03:59:24 PM

If the 0.1uF capacitor is polarised, it will be marked which end is positive and which is negative.

Most caps that small *aren't* polarised, so it doesn't matter.

Dj Task Manager · June 03, 2009, 01:00:37 AM

ARRGHH! Ive just tried to hook it up and now im totally confused...

I setup it as it is in the getlofi diagram and but it doesnt seem to work.
I can conceed that this is almost certainly dow to my ineptitude, i may have wired it up wrong and blown the chip up or something, what I dont get is when the switch is over selecting the crystal it works, then when I switch it to the other side for the LTC the crystal signal still gets through and it just keeps working?!!
what the hell is going on?! Im not very hot at electronics but this seems totally odd, maybe the switch im using is faulty? this is the only thing i can think of as there is no other way for a signal to get through!

once again AAARRGHH

Gordonjcp · June 03, 2009, 03:01:23 AM

Does it work with *just* the LTC circuit?