Roberts Expression DAB/FM Radio fault finding and repair

[Raufaser]

Hi,

My DAB kitchen radio stopped working. When it is pluged in, it powers on without having to press the power button. This is not normal. Normally you have to press the power button. The display shows information, but there is no LCD backlight. Usually the LCD backlight is always on when switched on and plugged in. The Power button does nothing. There is no audio out. The only way to power the radio off is to pull the plug.

This is an example of what the radio shows after plugging in the power supply:


The radio has to PCBs. One with the controls and display. The other one is for audio amplification (i guess). On the first one i noticed the following damage:


This is the whole board before cleaing (front and back):



The damage area after cleaning:


The whole board after cleaning:


Any suggestions what to measure or replace? Or any ideas in general what might be the problem and how to fix it. I would really appreciate your input. I am OK at soldering but a newb at fault finding.

Thank you in advance.

[cruff]

Looks like possibly C227 leaked. You should probably replace it.

[Koray]

I think the circuit could be cleaned further. There are still oxidation remnants left. Some components may require reflow of solder, too.
K.

[Raufaser]

Hi thank you very much for the idea. I replaced C227, but still the same issue. The desoldered cap had a tiny hole on the lower third of the body. But the cap tester says: ESR 0.49Ohms, Vloss 3,0%, 236uF ...Its specification says 220uF 6.3V
So maybe it wasn't defective despite the hole in it?!

C248 looks suspicious too. I will replace that next.

[Raufaser]

I replace C227 and C248. Still same same behaviour. I cleaned the board further.
Here are pictures of the current state:



Furthermore i tried to identify the ICs in that area. My findings
P0SV - RP200x SERIES Voltage Regulator  P0SV_rp200_ea-3219765.pdf (457.49 kB - downloaded 14 times.)
4013B - CD4013B Dual D-Type Flip-Flop  4013B_cd4013b.pdf (1203.32 kB - downloaded 4 times.)
26 A6K - AAT600 High-Precision Reset Voltage Detector  26_A6K_AAT600.PDF (336.32 kB - downloaded 11 times.)
29 8T - XC6202 High Voltage Positive Voltage Regulators  29_8T_XC6202_001.PDF (1858.46 kB - downloaded 8 times.)


I hope I am not too far off. I have no idea what the two "M6"s are and the "L6".

I measured the CD4013B and i didn't read a signal with my scope on the clock inputs. Is that normal?

Since all buttons are working except of the power button I will try to desolder this one. There was a lot of leaked stuff on this button.

There is a component missing above the "P0SV" voltage regulator. Can it be blown off? Dematerialized to dust?!. Or just an empty spot on the PCB?!

I really appreciate your inputs.

[fzabkar]

What voltages do you measure at SW204 and SW205?

Does the radio power up any differently if you hold down SW205?

As for L6 and M6 ...

http://markingcodes.com/search/c/L6
http://markingcodes.com/search/c/M6

"104" is a 10K pullup resistor on the CE pin of IC200. This enables the regulator. The missing component appears to be connected between the same pin and ground. I can only imagine that it could have been set aside for a small bypass capacitor which has now been left unpopulated.

[timenutgoblin]

Between D204 and C248 there is a resistor with "220" marking (22 ohm). It looks burnt.

[Raufaser]

Yes i agree. That has probably been me. In the first pic it looks normal. I am still measuring 22Ohms ...

[Raufaser]

Thank you very much for your input.

What voltages do you measure at SW204 and SW205?

SW204: lower pins 0.16V ; upper pins 3.43V
SW205: lower pins 7.7V ; upper pins 0.16V
(The other buttons like SW204 ; 7.7V is the voltage of my power supply)

Does the radio power up any differently if you hold down SW205?

No.

http://markingcodes.com/search/c/L6
http://markingcodes.com/search/c/M6

So many options. I have no idea which one they could be ...

[Raufaser]

I came back to report success in repairing the radio.

Short story:
IC203 didn't work as it should. It is a Flip Flop which forewards the operating voltage when flipping and flopping correctly. I supplied the voltage manually at it's output and the radio worked. Desoldered the IC to test it seperately. It worked correctly. Soldered it back in and it still works correctly. 

Long story:
After some evenings of unsuccessfully trying to firgure out what is the problem, because i didn't have any schematics and was only pretty much taking guesses, I decided to write an E-Mail to the Roberts support. I explained my problem and asked if they have an idea or can provide me with a service manual. Two days later I received a very nice E-Mail with the service manual attached. 
In there was a troubleshooting flowchart. I only had to do 3 steps ...



And the schematics helped in understanding how it is supposed to work.



So fingers crossed the TC4013 will work at least 10 more years.