aleph 5 help...please

[george a]

Hi All

I am in the process of firing up an A5 based onthe Mark Finnis boards

However some probs..
Positive rail fuses keep blowing and the negative rail voltage now also appears at the positive side of the pcb....
not good I'm Sure...

Can anybody offer any comments?

Thanks in Advance

[Netlist]

That must be a wiring problem.
Are you sure you didn’t reverse the polarities?
Try measure the PSU without connections to the amp.

/Hugo

[george a]

Hi

Actually the wiring is ok but it appears at least one output mosfet is shorted (on the ngative rail) _ I am going through checking the rest....

[Jye]

Hi George

I am also using Marks boards, just have to put the caps in. Is there any chance of you posting some progress pictures

Cheers
Jye

[george a]

Jye

I will post pics soon.
Boards are partly inverted in installation with semi's on bottom, now for ease of service and setup

Cheers

[george a]

Jye

Photo of heat sink assembly with "prongy bits" attached (wife speak)
this Aleph will be fan cooled (lots of fans left over from old PC power supplies!)

[george a]

Jye

Jye

part problem solved , ! output mosfet per rail fried (total 4)

Heatsink +pcb's shown in partial dissambly checking for probs
I'll post reassembled photo soon when amp up and running

Cheers

[george a]

Hi All

I now have some additional data

I read somewhere that to emulate the ouptut stage being ok but not connected that you short cap C11 (220uF) to ground
The out put stage is now NOT connected at all and I now get the following voltages:

R14 9.9 V (should be 4-5V)
Q5 0.56V (should be 4-5 V)
R11 5.6V (should be 4-5 V)
Z5 9. V = OK
Ground to source of Q1 & Q2 3.5V ( should be 4V)

Rail voltages are at 36V

I have checked all semi's and they appear ok.

ANy clues please ?????

[george a]

Hi again

I think I misred info on disconnection of the output stage.
I have now the whole circuit together excluding the output mosfets.
All other resisters etc are now in circuit .
Voltages now appear still as above excepting R14 remains at 9.9V

......help....please

[george a]

Getting there slowly..
voltages now as follows:

R14 9.9 V (should be 4-5V)
Q5 4.5 V (should be 4-5 V)
R11 5.6V (should be 4-5 V)
Z5 9. V = OK
Ground to source of Q1 & Q2 3.5V ( should be 4V)

BTW Jye

You will have noticed that the A5 boards I am using are not those Mark has in his own A5 but appear to be an earlier incarnation.

He lives just across town here in Adelaide.

I have seen and heard his own amp and the photos don't do it justice, he is a real craftsman.

AS for the sound - good enough to stop worrying about upgrading after getting it going.
Hats off to Nelson and to Mark...