Problem fixing an Amplifier - replacing electrolitic capacitors

[jmaarroyo]

Hi guys!
I'm new in this forum.
And I'm trying to fix and Old Onkyo a809 Stereo Amplifier.
Well everyhing started because, when I was listening some music in the amp, right chanel sometimes started to make some scratchy sound and sound got distorted.
I was reading in some pages that this is caused because some electrotic capacitors in the power suply leaks some AC voltage, this amplifier was made I think in 1992, so capacitors have almost 20 years, Original capacitors are 18000uf - 63 volts, I didn't find them, so I replaced them with some different value, 22000uf - 63 volts,
New capacitors are half of the size than old capacitors
It took me 2 hours to replaced them because of the cables, after that I turned it on, and it sound for a while, new capacitors got burned, and blown
Why does it happen?, is it because they're differente value, or because they're small size?
Any ideas would be appreciated.
I hope I could restore this old amplifier, it has a lot of power.

 

[Nigel Goodwin]

If the new capacitors have failed, then there's something seriously wrong - either they aren't the correct voltage (22000uF is fine, in fact it's an upgrade), they are faulty, or you fitted them the wrong way round.

 

[unclejed613]

sounds like you got them in backwards, or they don't meet the peak charging current rating of the originals. there's usually a half moon symbol or a thick line on the silk screen of the board indicating the negative side of the cap. also in amplifier and receiver power supplies there are very high charging currents (sometimes referred to as ripple currents) if the new caps aren't rated for this amount of ripple current (and you actually increased the ripple current when you increased the capacitance by the way) the new caps will fail. there's a third possibility, and that's that the new caps were some cheap knock-offs with a very poor formulation and wouldn't have lasted very long anyway. i usually try to get Panasonic, Elna, Rubycon, Nichicon caps for receivers. on the other hand Capxon, Samxon, Sam Yung, and other caps like that are cheap unreliable garbage.

the electrolytics that actually need replacing for the distortion problem are in the amp circuits themselves. there's one on the inverting input of the amp (the "feedback" input), there's probably one or more current sources that have an electrolytic across a voltage reference, and if the amp uses a "bootstrap" circuit in the voltage amp to increase total voltage swing, there's one or two electrolytics there. all of these caps in these locations can cause distortion or other problems.

 

[ben7]

oh no I think you put them in backwards!

I had a BIG cap almost explode in my face the other day, I could hear it bubbling inside! I accidently installed it backwards after it popped up out of the breadboard, I pushed it back down not realizing it got connected backwards! scared the crap outta me when I looked down at the board and saw it bulged up! xD

Must have been quite a smoke show with 22000uF caps! I wonder why no fuses popped at all...are the fuses for the positive and negative supply rails ok? How many amps are they rated for?(if there are even fuses at all...?)

BTW the old power supply caps were likely ok, you should clean out the front panel switches and volume potentiometer cause when they get dusty inside they tend to make the sound crackly.

-Ben

 

[shokjok]

Aside from reverse polarity or PSU failure, did you measure the power amp's supply voltage? It could be more than 63 volts, and you will need to connect 75V or 100V capacitors in parallel to achieve the desired 22000 uF. Is the transformer shorted?

 

[unclejed613]

a shorted winding on the transformer would be an instant blown primary fuse.... not more voltage...
the other circuit failure that could cause the caps to blow would be a shorted bridge rectifier, but he would have heard buzzing or hum out of the speakers if that were the case, and that would also more than likely blown a primary fuse. i still think it's backwards or substandard caps.

 

[jmaarroyo]

Hi guys!
Thanks a lot for your support!
Well I replace new caps for older caps, the only thing that got damaged was a fuse.
So I replaced the fuse and turn the amp on.
And it's working again!, I would have missed this amp, because It has a lot of power, I just have used 1/3 of the power.
I detected the problem and I saw that the "Input Selector" is motor controlled, so I used a bit of WD-40 to clean the input selector and the problem is gone!
I almost mess my amp!

So my theory is that new caps didn't produce enough power to support the amp.
Or may be they are defective, on cap got blown!
Now I'm listening to Diana Krall!
I promise be more careful, hehehe!

 

[ben7]

Hi guys!
Thanks a lot for your support!
Well I replace new caps for older caps, the only thing that got damaged was a fuse.
So I replaced the fuse and turn the amp on.
And it's working again!, I would have missed this amp, because It has a lot of power, I just have used 1/3 of the power.
I detected the problem and I saw that the "Input Selector" is motor controlled, so I used a bit of WD-40 to clean the input selector and the problem is gone!
I almost mess my amp!

So my theory is that new caps didn't produce enough power to support the amp.
Or may be they are defective, on cap got blown!
Now I'm listening to Diana Krall!
I promise be more careful, hehehe!

Yay!

Glad to hear you got it fixed!

It is very common to have dirty switches or dirty potentiometers in old amps!

Only one cap got blown? your sure you didn't put it in backwards? Thats very rare to get a defective cap.
Do you know what company made the capacitors?

-Ben

 

[jmaarroyo]

Repair Problem fixing an Amplifier - replacing electrolitic capacitors

Well!
I think this brand is unknow "NIPPON CHEMI-CON", only one cap got a bit inflated, it didn't explode because a fuse gut burned, I try to discharge the cap, but doesn't have any charge!, I discharged an old cap, and it had lot of energy!
I hope my amp could last at least 2 years, this amp (ONKYO a809) was made in 1991, I got it second hand!.
Does anybody know, about a website or dealer, where I could find this kind of caps?

thanks a lot guys!

 

[ben7]

Well!
I think this brand is unknow "NIPPON CHEMI-CON", only one cap got a bit inflated, it didn't explode because a fuse gut burned, I try to discharge the cap, but doesn't have any charge!, I discharged an old cap, and it had lot of energy!
I hope my amp could last at least 2 years, this amp (ONKYO a809) was made in 1991, I got it second hand!.
Does anybody know, about a website or dealer, where I could find this kind of caps?

thanks a lot guys!

huh thats very weird, Nippon Chemi-con caps are very high quality!

https://www.chemi-con.co.jp/e/index.html

-Ben

 

[jmaarroyo]

May be caps where stored very long time, because was very difficult to get these caps.
Nobody buys to often a bigger cap.
In fact, I will try to get these caps same size and capacity.

 

[Nigel Goodwin]

As we've all suggested, it's far more likely you connected it the wrong way round, it would die instantly if you did.

There's no problem finding such capacitors, they are common place - try Digikey - they actually list 9 different 18000uF 63V, and 10 different 22000uF 63V.

 

[unclejed613]

it's likely they were in backwards, that would also have been the cause of the blown fuse