aleph5 question

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I build an A5 some 2-3 years ago and it works like a clock (usually)

Today I listened to some low level music and it seemed that one speaker was completely dead. When fumbling with the speaker terminals it seemed that one off the connections was somewhat instable (it was completely lose inside and it bearly made contact and I never noticed before :xeye: )

So when I had done some resoldereing I couldn't resist taking some measurement and I noticed something strange...

1 channel draws 35V/10,7A at the powersupply while the other draws 35V/6.07A.
DC offset at the terminals is 38mVand 10mV.
So I measured some more, the fets are running at 2.87A both channels and voltage is also the same (0.6 V). When connected to a sinewave generator output is the same with an 8ohm resistor.

Can someone explain where those 4 amps are going ???

Ralph
 
an idea...

there are 2 options I can think of, assuming totally separate PSUs, check your rectifiers, and then check your caps, I had one that was not a dead short, but close to it, and given long enough it would have gone poof...I found it after noticing it was getting warm...

Stuart
 
first...

...check with your meter for the resistance of the bank as a whole. After a while it should approach a huge number, the meter has to charge all the caps, but if one is bad it will not climb past a certain point...if it shows up as shorted, then you can start unsoldering...

Stuart
 
Ok,

now I know how important it is to build your amplifier servicable ??!!

I had to dismantle the complete amp to get to the rectifiers (stacked under 2 layers of caps which were bolted to a plate and the plate was bolted to an other plate which had a screw under the main pcd ?!!!).

Since this was my first real project I was now horrified with my solderingtechnique...

So what did I do:

I disconnected the amp from the PCB --> still 4A lost
then I disconnected the last 6 caps per channel --> still 4A lost
then I disconnected the first 6 caps per channel --> still 4A lost

at that point I only had the rectifiers and trannies to the wall. So I disconnected the rectifiers, but by then I coudldnt reconnect power in a safe manner so I measured the diodes in the rectifiers which seem fine ?? so now I came to the only part left, the tranny....

So my next step is to take apart the groud plate whith the transformers and measure them.

When will I build an Aleph-x ???, whenever the A5 is running again :bawling: :bawling: :bawling:
 
I first measured the left channel +/- compared to ground and did the same with the right channel. These steps I repeated until I got to the rectifiers.

I'll probably rebuild only the PSU on a piece of MDF this weekend so I can work much safer and can measure trannies,rectifiers and caps

Ralph

ps I use some generic bridge rectifiers

pps all the way down there were the rectifiers (pic shot at original build, it's a sad sight now)
 

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I’m not sure but could this happen with wrongly connected secondaries?
I remember ones connecting the wires of dual secondaries the wrong way.
Heavy current was running so I rewired and didn’t bother anymore to test if the circuit would have worked.

/Hugo
 
maybe...

...If secondaries were connected in parallel, but did not match perfectly, ie one had a turn or two too many. In most cases the current would be quite high, four amps is definitely possible. The impedance of the secondary on a big toroid is a fraction of an ohm, and the torids I've played with had about 2-3 turns per volt, so a even one turn imbalance could make a 0.5v difference.

Either disconnect and measure or use a clamp on current meter and measure with no other load, it would show up immediately...

Good luck

Stuart
 
Hi Jan,

going to the ddiy_2005?

For my A5.

I didn't have time so far to rebuild the PSU on a small board. I only did some parametric measurements on the caps en the strange part is the left channel is going to infinite ohm en the right is holding at about 0.140mOhm, all caps on that side :confused:

Ralph
 
I found...

...that in my case one of the caps was dead and 'nearly' shorted. I had fitted one of them backwards, if you have checked this then it must have been bad to start...or there is a piece of something shorting the pins...

You're nearly done...just have to check each cap in turn for temp...be careful, if it really is soaking up that much current it is eventually going to fail with spectacular results..

Stuart
 
Did you watch the polarity of the ohm meter with respect to the caps? If you hook the ohm meter to a cap with reverse polarity, the cap won't charge and will show maybe even negative resistance.

I'm inclined to believe a bad cap that had been sucking up 4A would have had a violent reaction by now.
 
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