DDS generator problems

[Deathwish]

I purchased one of these a while back. http://www.ebay.co.uk/itm/291399023398?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I attached it to an atx psu, and then a psu I just finished making last night. All I get out of it is freakiness. I cant give you a pic as my phone camera is broken, but if you draw a sine wave and then along its entire length place masses of white dots that is what my scope shows. if you then wait a few minutes the waveform starts to look like someone has put a sandcastle on top of another one on each cycle.

It is doing my head in. Any ideas

[electros6]

Does the lcd power up. what is the scope you are using , please provide some details

[Deathwish]

lcd is fine, scopes are a tektronix 2225 and a rigol ds1054z

[mij59]

Could be a problem with the output filter of the generator, whats output level and frequency of the generator ?
With the Rigol you should be able to save wave forms to usb

[Deathwish]

Sorry was busy trying to play with it. It is now showing me a double sine wave ..... then it turns off, so I think it is kind of naffed, but the psu is fine so thats good..

[Farley]

This looks like the same device in another auction:
http://www.ebay.co.uk/itm/DDS-Function-Signal-Generator-Module-Sine-Square-Sawtooth-Triangle-Wave-Digital/400971779496?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20140122125356%26meid%3D7a90dc301d8646c0864eda7b437897df%26pid%3D100005%26rk%3D2%26rkt%3D6%26sd%3D291399023398

In the schematic shown in that listing it doesn't appear that there is a decoupling capacitor on the AVR power pin. Assuming the module you have has the same processor, you might try adding a 100nF cap directly across pins 10 and 11 of the AVR. Keep the leads a short as possible. Also, it doesn't appear there is any decoupling on the LM358 power pins.

Another thing to try would be to re-seat anything in a socket or connecter.

After that, if still no joy, look for poor solder joints and/or retouch/reflow all the solder connections on the PCB.

[Deathwish]

yes thats the pos, it is now on LSD, the screen is doing funky things and displaying random char$ and then it turns itself off at random. It is in the cupboard till it learns to behave.

[Deathwish]

the user manual etc

https://www.dropbox.com/s/z0ktc666sct1gj1/H11887install.pdf?dl=0

[tom66]

Bear in mind the output filter these use is very basic, essentially nonexistant, so don't expect a clean wave at a high frequency unless you're prepared to add an external filter.

[Deathwish]

I can do that I suppose if I can find one

[jimdeane]

Does the PSU need a minimum load, and do you have a load resistor in place?

[Deathwish]

No its not the psu, I tried a atx one then built my own , it does the same on both. for some reason i purchased an ad9850 module and a ublox lea 4t gps receiver too, I cant remember exactly why , I think i was going to make a sig gen of my own but I lost all train of thought on it a while ago.