Sandstrom DAB Radio -

[Gabriel]

Ok, the radio turn on but the display flickers on-off quite fast, nothing is displayed - caps look ok but may be toasted anyway.

So what would cause the display to behave like this ? Is this perhaps a psu problem and a cap that shorts to ground ?
When I measure voltage to the display it varies between 3.003 to 3.025 quite fast, is it possible that the voltage varies even more but that my fluke 12 don't have the brains to detect it ?

Added a few pictures and a 10MB video showing display behavior.

Video link to photobucket - http://s636.photobucket.com/albums/u...t=MVI_2963.mp4

[japlytic]

On the 5th picture, try replacing the three electrolytic capacitors in the bottom left corner, including the 1000uF 10V unit near a 3-pin through-lead IC (transistor-like package).
If the radio works properly, replace the electrolytic capacitors on the primary side.

[Gabriel]

Thanks will remove them and try with some others - why would changing the primary caps help if it works after replacing the other 3 ?

I tried to use the min/max feature on the fluke on the voltage to the display - max was 3.1.. and min was 0.017 - If thats correct I'm guessing that the caps short to ground.

[Gabriel]

Replaced the 3 of them no change, replaced the 2 to the left of them too no change.

Will try so more the following days.


Any other ideas ?

[momaka]

There's a small capacitor by the PWM/FET IC on the primary side, likely 10, 22, or 47uF - this is the start-up capacitor. Replace this capacitor (if you haven't done so already).
If you have and the results are still the same, note down the part number on the PWM/FET IC and post it here. Also measure the voltage across that start-up capacitor. BE CAREFUL! The start-up capacitor is on the primary side, so you'll likely be measuring its voltage with respect to hot ground (this is not the same as the regular ground).

[Gabriel]

Yes, it was the startup cap - 47µF 25V Jwco - Can't even find their homepage so I fitted fm pretty much all over.

My fluke measured the startup cap to 47µF - guess a esr meter would be quite handy.

Everyting works now - Thanks momaka

[momaka]

You're welcome and congrats on the fix .

[Little Al]

I know this thread is over 2 years old now. But if any one is still browsing, your help much appreciated. I accidentally left the radio on for 2 weeks while on vacation. It was still working but the display brightness had gone. In a darkened room the display can be seen running. In normal lighting conditions the display is invisible. I have looked for "cooked" caps but there seems to be none. If anyone can point me in the right direction, I would be most grateful

[Gabriel]

Welcome to the forum.

My caps did not look cooked at all, caps can fail without bloating.
The 47µF 25V Jwco was the only defect cap in my radio - I did however replace all the Jwco as they are totally crap.

Added a picture for you to see, try to replace the small 47µF next to the two kmg's.

[Little Al]

Hi G

Thanks for the picture and the info. Am sorry to appear to be an ignoramus but what are KMGs

Al

[Gabriel]

In the middle of the picture right behind the transformer you can see two caps that are brown in colour - they are marked kmg - to the left of those two you can see a small black cap.
That small black cap was the only caps that was defective in my radio, replace your's and see if it comes back to life.

[Little Al]

Thanks for pointing me in the right direction. Will let you know how it goes