advertisement


4 terminal capacitors

Thanks snoman.
Any colour - LOL. I very much doubt she's going to have green, I have a funny feeling these could end up red, having said which I don't think she paints her nails. Maybe she'll have clear.
I've tried to clean as best I can, the problem with cleaning to the left is there are so many components the cotton buds just keep getting caught on them. I'll have another go. At least to the right they are in fairly straight lines.
I can't take offence at blobby, I'd have to agree. I'm pretty sure I was aware of this when I did the caps a while ago and took a meter to them to check there was no conduction, but I'll check again.
 
I possibly should have mentioned. I know there is a stained / darker area between the mosfets and the screws, behind that there are not any caps, so I don't believe this is electrolyte - most likely rosin as you say. The caps are in 3 rows, the straight line of lots of blobby soldering, another row to the right of that and another 4 caps immediately to the right of the mosfets, each of which I think are now fairly clean.
I did check the resistance between the long line of caps terminals and they either have no conduction or resistance of around 1.96 on the 2k Ohm scale, which I think agrees with the surface mount resistors in each case.

Correction - the long line of terminals is the backs of untouched mosfets (the groups of 3) and replaced caps (the wider pairs of terminals)
 
Well I appear to have fixed my problems on the worse (right) channel, but I still have a little crackling on the left channel when I turn the amp on for 20secs or so.

A question please.

How quickly do the mosfets heat up to dangerous (damaging) levels if not connected to a heat sink (with nothing on the input)?
Disconnecting / connecting the heat sink from the mosfets is a right PITA, fiddly and takes forever, if I can turn the amp on for a minute or so to check for crackling without damaging the mosfets that would help a lot.

Thanks.
 
It all depends on how much bias is present but mosfets tend to be operated at higher bias than bipolars. It could be anything from 20 seconds to a minute or two... use your fingers to tell if you don't have an infra red thermometer. If they are too hot to touch for more than a few seconds then they are too hot.
 
Well firstly thanks to all those who offered suggestions but I think I'm going to have to concede defeat, although it was entertaining trying to fix it.
What I did more recently notice is that if I put a voltmeter across the amp o/p terminals, the right channel would get a spike (20V+ from my amateur voltmeter so probably more like 60V in reality) when I turned it on. Out of curiosity I did try swapping the large caps between channels and the spike also moved. What I suspect that also means is that I had some other fried components / shorts on the original channel and I've now fried some more on the other channel. I did also notice after swapping the caps that after the spike the voltage went to 0V and after I turned the amp off gradually increased to around 4v over 10mins or so before decreasing again.
Oh well.
It was a lovely amp but time to say goodbye to it.
Thanks again.
Jeddy
 
You must log in or register to reply here.


advertisement


Back
Top