Roberts Radio rd-3 FM RDS/DAB digital radio
Not working

No sound
Fuse blown

22nd July 2017

Fault: no sound, no display

NOTE: if the fault is no sound, but the display is working (and the radio tunes as normal),
then the fault is likely to be the headphone socket contacts. These buld up an oxide layer over time, particularly if
the headphone jack is not used for a while. In that case, simply insert and remove headphones in that socket
several times.

This report is regarding:

Status: red mains light on, but radio dead with the "On/Off" button either on or off.
No display and no sound.


Faults discovered::

The 800mA fuse had blown.

C49 was of the wrong voltage rating. It was rated at 10V, but was across the 15V* supply
This is a design or manufacturing fault..
C49 had "exploded" and blown the 800mA fuse.

Also, there was no 15V continuity between C49 and C52, most likely the via hole at C52 was damaged by the current surge.
This meant there was no supply to the audio amp, hence no sound.




A link was placed in the position shown in the image below.


The capacitor C49 was removed.
Because of the difficulty in inserting a replacement (only limited tooling avaiable), it was not replaced.
It merely doubles up the decoupling that is already supplied by C52.

The radio appeared to work ok without it.

Anyway, the disc ceramic C48 provides high-frequency decoupling locally to the Audio Amp.

This is the view from the other side of the board, showing the position of C49:


Testing was done with a lab power supply set to 15V, connected after the 800mA fuse holder.

Even though this may not be the only fault that may occur with this radio, I thought I'd share it online, to add to the fault reports available.

*15V supply: this was what was measured before the 800Ma fuse, being the off-load voltage from the radio internal power supply.
I therefore tested the radio with a regulated 15V power supply, which caused C49 to blow, I assumed for the 2nd time.
However, since inserting a replacement fuse, I noticed that the radio internal power supply dropped to just over 10V.
Even so, C49 should still have been rated above 10V, typically 15V.

Please let me know if this was the fault you had, and if this report has been helpful.
Click the button below.


For those of you interested in the Audio Amp Data Sheet, here it is:








roberts radio rd-3 FM RDS/DAB digital radio
not working
no sound
fuse blown
mains lamp on