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Old 16th September 2003, 09:17 AM   #1
Lucas_G is offline Lucas_G  Netherlands
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Default Problem with one Aleph 2 channel

Hi Pass builders,


Recently I fired up (for the first time) two Aleph 2 power amps, equipped with Kristijan's pcb's.

One channel immediately worked fine, but the other one did not.

There was a little bit of smoke, and when I looked at it, it turned out that on the driver pcb there had been an electrical shortage.

The lead on the driver-pcb that goes from POWER + (45 VDC power in) to INPUT ground (both balanced and unbalanced grounds of input) has broken because of an electrical shortage.

BTW, I could not retrace this link between PSU + on to the input grounds on the schematics... Can anyone explain this link?

I examined the PCB, but I could not find any misstakes up till now.

The only thing I can think of is that I may have exchanged + and - power... (you never know!) when connecting PSU and Driverpcb...

Does anyone have any suggestion what might have been wrong?


Regards,

Lucas.
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Old 16th September 2003, 07:45 PM   #2
Lucas_G is offline Lucas_G  Netherlands
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Does anyone have a clue?
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Old 16th September 2003, 07:53 PM   #3
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Did you ask kristijan for an opinion?
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Old 17th September 2003, 09:43 AM   #4
Lucas_G is offline Lucas_G  Netherlands
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Quote:
Originally posted by Tazzy
Did you ask kristijan for an opinion?

Thanks Tazzy for replying.

Yes, I did contact Kristijan, but I am afraid he is on holidays...

I also received this message from Dane:

"The lead on the driver-pcb that goes from POWER + (45 VDC power in) to INPUT ground (both balanced and unbalanced grounds of input) has broken because of an electrical shortage."

On the schematic:
http://web.vip.hr/pcb-design.vip/aleph-2.gif

There is NO connection from +45V to the Input Grounds... Was this part of the assembly instructions?

This could be why nobody has responsed.

There are various threads on the forum on Aleph Troubleshooting. Unfortunately they all read about the same... "Remove all components and test them. Replace any that measure bad or unusual, and reassemble the amp correctly"

I would hate to have to unsolder the output and current source transistors and test them. that was the most difficult part of the construction! (well maybe not - but still a pain)

If you reversed polarity, then yes something probably did fry.

"(you never know!) " You would HAVE to know.

If something smoked, and it wasn't the wire between +45 and Ground, then it's either a transistor or source resistor most likely, and they all have to be checked out of circuit.

I didn't use a variac and bring the amp up slowly while measuring things. I was lucky. My Aleph 2's have been running almost 1 year now.

Test the transistors using the Transistor Matching article on the passdiy web site."


Thanks Dane for replying!

Actually I DID match all the transistors, and I DID check all the connections. My first project Aleph 5 monoblocks were ok right from the beginning, so was the other channel.

I was just as astounded by the connection between PSU plus and Input ground....???!!!!!!!!!!
However, I could not compare this driver-PCB with the other PCB in the working channel....

BUT!!!!!!

This morning I looked more closely in daylight at the PCB....:

KRISTIJAN, THIS REALLY SHOULD NOT HAPPEN!

There is a (unwanted) connection (actually a tiny, but beautiful lead) between the PSU plus plane and the ground plane!!!!!!

Mystery solved!

I will ask Kristijan to send me a new driver PCB, and meanwhile repair this burned pcb, and remove the unwanted connection by scretching it out.

Regards,

Lucas.

Here is a picture of the pcb:
Attached Images
File Type: jpg faultypcbwithtextsmall.jpg (50.7 KB, 622 views)
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Old 17th September 2003, 09:45 AM   #5
Lucas_G is offline Lucas_G  Netherlands
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Here is a close up picture of the spot with the short-circuit:
Attached Images
File Type: jpg faultypcbdetailwithtext.jpg (56.2 KB, 606 views)
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Old 17th September 2003, 01:11 PM   #6
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Hello Lucas,

I am sorry to hear about your problem.

Also, I am glad that you located the problem precisely.

I believe that the all parts that are located at the PCB are in
working order, and are not affected by this short circuit.
You should power up the amplifier again, once you
reconnect the melted PCB leads and remove short circuit.

The new replacement board would be send to your adress within 24 h.

If I can be of any further assistance to you please feel welcome
to contact me again.

Best regards,
Kristijan Kljucaric
http://web.vip.hr/pcb-design.vip
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Old 17th September 2003, 06:50 PM   #7
Lucas_G is offline Lucas_G  Netherlands
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Quote:
Originally posted by kristijan-k
Hello Lucas,

I am sorry to hear about your problem.

Also, I am glad that you located the problem precisely.

I believe that the all parts that are located at the PCB are in
working order, and are not affected by this short circuit.
You should power up the amplifier again, once you
reconnect the melted PCB leads and remove short circuit.

The new replacement board would be send to your adress within 24 h.

If I can be of any further assistance to you please feel welcome
to contact me again.

Best regards,
Kristijan Kljucaric
http://web.vip.hr/pcb-design.vip

Hi Kristijan,

Yes, I am glad too that I have found the problem.
It drives you mad when you think you must have made an error and are unable to find it.

However, such small accidents happen.
I will make this pcb working for now, and when the new pcb arrives, i will exchange it.

Apart from this particular pcb, I have always been very happy with your beautifully designed pcb's, so keep up the good work!

When this project is finished, I will order some Aleph P 1.7 boards with you. Maybe even a group buy, since my friends have become diy-pass lovers too!

With kindest regards,

Lucas

P.S. Yes, the address is right...
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Old 24th September 2003, 10:03 PM   #8
Lucas_G is offline Lucas_G  Netherlands
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Quote:
Originally posted by kristijan-k
Hello Lucas,

I am sorry to hear about your problem.

Also, I am glad that you located the problem precisely.

I believe that the all parts that are located at the PCB are in
working order, and are not affected by this short circuit.
You should power up the amplifier again, once you
reconnect the melted PCB leads and remove short circuit.

The new replacement board would be send to your adress within 24 h.

If I can be of any further assistance to you please feel welcome
to contact me again.

Best regards,
Kristijan Kljucaric
http://web.vip.hr/pcb-design.vip

Hi Kristijan,

The new pcb arrived today. Thanks for sending it quickly.

Today I tried to fire up the channel again with the repaired first pcb.

It did work, however I got a DC at the loudpeaker outputs of 9 Volt DC!!!!!!!!!!!!!!!

I switched off, then fitted a 5 Watt 10 Ohm resistor as a load, and then switched it on again. The resistor immediately melted away.

What could be the reason for this extreme offset?
I did the same matching as with the other channel, on which I get a DC offset of 0,01 Volt...

Could it be that some transistors were damaged by the shorting circuit of the faulty pcb. There had been a shorting betweed PSU plus and Input grounds....

What transistor is most likely at fault? The BC550's or the 9610's?

Am I right in presuming that if one of the 240 power mosfets were defect, I should get something even higher than 9 Volt DC (my PSU delivers 48 VDC).?
Also the powermosfets should be more immune against such a 48 Volt shortage...??

I sincerely hope so, because exchanging transistors on the driver pcb is less of a pain than desoldering/removing and checking all the powermosfets...

Any help from someone with insight is dearly appreciated!!

Regards,

Lucas.
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Old 24th September 2003, 10:07 PM   #9
jleaman is offline jleaman  Belgium
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On this note. I to admire your pcb's and work kristian. : O ) Please do keep up the good work..

Hope to hear from you soon. as i need to order boards also.
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Old 25th September 2003, 01:04 AM   #10
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I would say that it is highly unlikely that the power fets ar damaged. As you said, if one was damaged, you would have full rail(- or +) at the output. however, if one was shorted on the pos side and one on the neg side, you could see something else, but you would also see some flames and majic smoke come from the source resistors.
Since Kristijan sent you a new board, I'd maybe salvage caps if you think it's cost effective and replace all transistors andjust pitch the old board. you can test the power fets as sets with a ohm meter. You should see near infinite between sources and drains and gates.
I had problems with both of my Aleph 2+ s and studied the circuit until I could almost draw it from memory. Don't let it discourage you. When you can become one with the machine, you can understand it to the point of knowing what it will do if you change anything.
Good luck and keep us posted.

And let's see some pics of the chassis!
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