Capacitor Question

[caraudioguy2100]

I’m staring a new thread on this since my old post has my questions along with others questions I wanna make it less confusing .

Anyway I’m rebuilding a 10k amp and noticed the amp has Sam Young caps in it .

i tested the rail caps which are supposed to be 1800uf 200v caps .


Some of the caps tested good while others tested not so good .

2 tested at 1660uf another at 1200uf and the esr varies from 2.4 to 1.6 .

I’m going to replace all of the rail caps .

Since the rail cap readings are all over the place wondering if this would be the cause of the amp self destructing when I installed it in the vehicle?

 

[Perry Babin]

Are you using 21844 driver ICs?

When did the amp fail (on startup, on shutdown, after being driven hard...)?

 

[caraudioguy2100]

The amp is using IR21844 driver ic’s . The audio driver board was brand new when I installed it .
The amp failed on power up .

The amp worked perfectly fine on the bench but when installed in a vehicle it self destructed

 

[Perry Babin]

Is the initial mute delay working... Does the rail voltage build completely before the amp starts to oscillate? See attached.
http://www.bcae1.com/temp/ampstartup01.mkv

 

[caraudioguy2100]

I will have to check this out after I replace the caps since they are out of the amp at the moment and I’m waiting on the power supply fets to arrive

 

[caraudioguy2100]

Also wondering can I replace these disk caps (tan colored) with these ceramic caps ?

 

[Perry Babin]

That appears that it's likely just across the 12v input. If so, the replacements will be OK.

Why are you concerned that they wouldn't work?

 

[caraudioguy2100]

Well there is a few that were damaged after cleaning the board in the protection circuit so was wondering if these will work just as good as the originals . I took the pic as reference to show what caps I was referring to

 

[Perry Babin]

As long as the voltage rating of the replacement cap is well above the applied voltage, they should be fine. You'll have to determine what the applied voltage is.

Is there a voltage rating on the original caps?

 

[caraudioguy2100]

No there is no voltage rating on the original caps

 

[Perry Babin]

That 'generally' means that the caps are rated for 50v.

 

[caraudioguy2100]

Back to this amp . I’m ordering new rail caps for it somce the old ones were way out of tolorance . I can only find 85 degree caps . Should I keep looking for 105 degree ? They are 1800 uf 200 v

 

[Perry Babin]

For the most part, the primary filter caps are 105C. The rail caps are 85C.

 

[caraudioguy2100]

I’m onto the next section of this amp . The outputs filter caps are 10uf 250 volt caps which are impossible to find .

There are a total of 4 caps 2 caps are in parallel with each other same with the other 2 .

My question is can I get a total of 2 caps . 22 uf 250 v film caps to replace the 4 10 uf caps and hook 1 lead here and the other lead here as shown ? Since space is an issue . Or will this not work ?

 

[Perry Babin]

Yes if you can find a 22uF@250 that will fit.

 

[caraudioguy2100]

In the schematic the output filter caps appear to be in parallel. The originals are 10uf 250 v .

i ordered 4 caps total 22uf 250 v.

can I use 2 per side and use both positives soldered to the board as shown and hook the negatives together to make the new filter caps ?

 

[Perry Babin]

You were asking about film caps. Did you buy electrolytics?

If so, the series connected electrolytics are generally each rated for at least double the full rail-rail voltage.

 

[caraudioguy2100]

I couldn’t find any film caps that would fit in the allowed space . I bought electrolytic’s .

so I need to buy 500 volt caps instead of 250 v caps if I run them in series ?

 

[Perry Babin]

What is the rail cap voltage?

 

[caraudioguy2100]

200 volts