Loud random pop from Technics amplifier

[dg0991]

Hi everyone, My Technics su x 120 amp has recently stated to crackle and pop loudly randomly, irrespective of the volume. It starts by crackling and them makes a very loud popping sound sending the speakers to the limit of their throw.This mostly happens when the amp is powered on after being disconnected from the mains for a couple of hours.It rarely happens if the amp has been left plugged or switched on.

Also when the amp is connected to the mains after being disconnected for several hours it does not power on at once, meaning that I have to push the on off button several times to get it working.Once the power lights come on it crackles and makes a very loud pop sound.This happens regardless of the input selected.

I'm thinking that maybe some capacitor has gone bad?

 

[petehall347]

sounds like a power switch issue ..or power relay if it has one ..

 

[dg0991]

Thanks for your reply.It does not have a power relay, I thought it was the power switch at first but if it is the power switch would the amp make the pop noise at other times as well?

 

[petehall347]

i think it would arc then burn itself together enough to work until its turned off and back on .
you could try and listen to the switch itself at power up when its acting up ..

 

[dg0991]

I checked the switch with a multimeter and it seems to be working fine, there is also no evidence that there was any sparking or a loose connection, I forgot to mention that when powered up after being disconnected from the mains the display backlight comes on the first time meaning that the amp is powered, however the display itself and the surrounding lights do not come on.

After this the amp will work fine but sometimes it will make a loud random pop.

 

[petehall347]

pops are generally transistors gone bad .. power on crackling is often the power switch .
is it both speakers ?
does amp have main-pre jumpers .?
if both speakers i am suspecting power supply transistor/s or poor soldering .

 

[dg0991]

Yes it affects both speakers and the loudness of the pop is the same regardless of the volume it is turned to, the amp has never been taken apart and has not been used a lot before I bought it, however it had been stored in a damp place.

 

[petehall347]

if you are certain about the power switch next logical move would be check for dry solder joints around the power supply . i use a magnifying glass so i can see stuff much better .
also check any fuse holders for corrosion .

 

[Alanthefuxer]

I bought one of these amps today and when I plugged it in first I thought it was going to take my speakers out, with a LOUD 'whump'. I switched it off in a hurry (to save my Tannoy D700s from damage) then opened it up. All I did was push down the large 3300 cap on the PCB behind the power switch and there was a loud click. I tested it with headphones - ok - and when I connected again all was well. I'm sorry I don't know what this proves, but the PSU area on the board seems suspect to me. I might take it off and do a recce of the solder joints, but probably only if it misbehaves again. All of the caps look perfect by the way!