Carver have internal fuse to protect channel dead?

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi doggie750,
There are no internal fuses in a Carver, save the mains fuse. This seems to satisfy the anti relay / fuse lot but they still don't like Carvers.

There is a known failure that can cause this. One leg of the the input coupling cap one the long PCB's breaks free (broken solder connection). It simply needs to be resoldered. Look for a film cap near the top back from the motherboard.

-Chris
 

djk

R.I.P
2001-02-04 4:23 am
USA
Its a little more complicated than a bad solder joint.

Carver liked to buy surplus parts where available. The 'greenies' have copperweld leads, steel plated with copper, then tinned. The steel to copper bond fails. The solder joint may look fine, sometimes wicking it and re-soldering will fix it (for a while).

The best thing to do is replace the cap with a polypropylene with pure copper leads, they cost less than $1 each.
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
All due respect, but I have never had a Carver come back with that joint failed again. Possibly you saw one production run because they would definitely have put out a bulleton on this. Even if they didn't, I used to talk directly to the engineering staff and service and this was never mentioned. The joint did fail in many units. Our fix was to desolder the joint and redo it with a touch of flux. The amp may be back blown, but never that joint again.

I have seen amps where a tech had cracked the side off the cap and / or destroyed the traces, but that's all for that cap in particular. If it makes you feel better, replace the film cap with another of similar value. Using adhesive to couple the cap to the board will help keep the joint from cracking again. Djk, perhaps this step was missed?

-Chris
 

djk

R.I.P
2001-02-04 4:23 am
USA
It strictly depends on the age of the capacitor. Using NOS surplus parts caused the problem, being quite old when the unit was built. Not all Carver units had these parts, no easy way to tell.

I am also seeing the same problem with carbon film resistors with copperweld leads in several different brand amplifiers that are about 20+ years old.

This and gold migration have been a real PITA on a few units until I figured it out.
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi djk,
I also see this on many different brands. Mostly Asian production. It appears the leads are not properly prepared before the solder bath. Either that, or the wave soldering machine is poorly maintained.

I normally remove the component and clean the leads, then reinstall. Replacement achieves the same thing. Electrolytics are replaced. But then, these days, only the older stuff is worth repair unless you are talking about the better brands.

-Chris
 

djk

R.I.P
2001-02-04 4:23 am
USA
At the risk of repeating myself, it is the plating that has failed, not the solder joint.

If you are near Cedar Rapids, Iowa let me know and I will see if I can get you a visitors badge. We have some scanning electron 'scope photos that you might find interesting. You might have to sign a non-disclosure agreement.
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi djk,
Well, that's certianly possible. Whatever the actual cause, the fix seems to be the same. I don't have access to a scanning electron 'scope, but I will believe you on that. I can only speak from what I've seen come across my bench over 30 yrs. I do like to chase faults down to their actual cause.

Wouldn't be the first non-disclouse I've had to sign. If I ever get down there I'll have to look you up. Sounds interesting. I'm up in the Toronto area. Kinda far for me to "drop on by" :D .

Take care, -Chris
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi doggie750,
I can't remember the colour of the cap., it doesn't matter. The solder joints will look fine as djk and I were discussing. The cap in question is a film cap near the top side closer to the connections to the board that runs front to back. While you are at it, clean and resolder those joints too. It is a pain in the butt, but I've had to do this many times over the years.
Just take them all out and clean / tin the leads and resolder them in. You can replace them if it makes you feel better. I believe there was some silicon adhesive holding the cap in question down on the PCB.

-Chris
 
I think I know which cap is it.....Your are right about the silicone bonded to it on the pcb. Prior to taking this out, would it be wise to test the cap first if this is the right cause of the failed left input. What's the next step if we are targeting the wrong object, let say the cap is good and still intact?
You are right it's a pain to tweak this out. but it's FUN...challenging

Much thanks
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi doggie750,
To "tack solder" means to temporarily solder a connection. In this case a capacitor across a suspected bad capacitor. Do this with the amp off -of course.

Running the amp. Yup, turn it on. The cover will be off so no jewlery allowed! There is around + and - 120VDC on the high supply. Use a plastic rod or something like that to manipulate the components. No metalic probes allowed.

When you turn it off and unplug it (hint!), use a meter to be sure all supplies are discharged. Do this before soldering anything.

-Chris