Repairing clock radio

[unchillfiltered]

I have a clock radio alarm which I'm quite fond of, and which has reliably woken me up every morning since the late '80s. It has recently started making clicking noises at random times, a similar noise to what it normally makes when the radio comes on.

While it would be far easier just to bin the whole unit and get another one (or simply disable the speaker and use it only as a clock), I would prefer to repair it.

My not very educated guess is that one of the capacitors is not holding its charge, and I reckon the two blue caps at the front left of the image below may be the problem, as there appears to be a slight residue below them.

They are 470uF and 220uF (both 10V), if that's any help.

Does anybody have any suggestions before I do anything more?

 

[davelectronic]

Clock radio repair

Hi unchillfiltered.
Its a possibility, daily use and of that age, but the stuff at the base of the caps looks like a bonding compound, pcb manufacturers often use the stuff, as ive tried to reclaim the odd cap from a newer dead electrical item.
Dave.

 

[shrtrnd]

The clear plastic cube with the pink dot on top looks like it might be a relay.
The relay would be more apt to make a clicking noise.
Trace the wiring on the bottom of the board from the power to the relay, it should
lead you to the (possibly) bad cap.
good luck

 

[davelectronic]

Clock radio repair

Ive plugged in old power supply's of, or from the 80's powers ok until you load the supply, it soon becomes apparent the capacitors are dying.

You could re cap that in a short time, if you do find the offending capacitor, then for lasting longevity, i would be inclined to replace them all.

That does look like a relay, but it might be an inductor, it can really only be one or the other, pin out on the underside might give some ideas, as would closer inspection of what is possibly the relay, bad cap would make it judder, if voltage dropped across the coil.
Dave.

 

[Resqueline]

The cap's look ok but might still be going bad and cause problems. You can try to measure the ripple voltage on them or you can just replace them.
The clear plastic cube with the pink dot on top is a radio circuit inductor. It has nothing to do with this issue.

 

[unchillfiltered]

Thanks very much for your prompt responses. As a newbie to this board I appreciate your assistance.

I can't see anything which looks like a relay on the PCB, but think the radio may be switched on via one of the two small ICs on the board rather than a physical relay. The clicking noise I refered to comes from the speaker.

I'll need to get some new capacitors and try replacing these. There's nine electrolytic ones, which I expect are most likely to be the problem, and loads of small ceramic ones which are probably ok. Part of the board has an epoxy resin coating an I don't have any inclination to attempt to remove that.

 

[shrtrnd]

The random clicking noise sticks in my mind.
Any possibility of dirty switch contacts or volume controls?
The caps sound like likely suspects but the random clicking seems unusual.
Dirt or moisture a possibility?
I had an annoying clicking in the audio of my TV years ago. It was sitting under my
evaporative cooler vent, and moisture was getting into it.
Just something else to consider.

 

[unchillfiltered]

shrtrnd, I'm pretty sure it's not related to the switch or volume control, but I'll wiggle these about to check first, as that's easier than replacing the capacitors.

 

[poor mystic]

"Easy, scmmeezy" is what you should say, unchillfitered.
If this really is a sentimental item replace all electrolytics; they are born to die and don't live all that long.

 

[shrtrnd]

I suppose it's a long-shot, and I haven't heard the clicking noise. I was just wondering
if it might be static from dirty contacts on old switches. You'd use spray-can electronics
parts cleaner for that. May not be the problem, but thought I'd mention it.
Worn/dirty volume control on radio might cause intermittent static 'clicking'.
poor mystic is right though. Over 20 years on a clock radio is considerable. They
really AREN'T designed to do that.
Good luck with the resurrection.

 

[poor mystic]

It could most easily be as you suggest, shrtrnd