help needed aleph 2 troubleshooting

[MikeZ]

Here is the problem: when I switch the power on there is about a 3 second delay and then my 4 amp circuit breaker blows. This is not giving me time to find the problem in the circuit via taking measurements. Any suggestions?

Here are the specific details:

First I have only basic electronic skills so try to address your suggestions to my low level of knowledge.

This is an aleph 2 monoblock.

The power supply is Kristijan K design.

The main circuit board is BrianGT.

The power supply to the boards is 51 Vdc per rail.

I had a friend double check my wiring and he found no mistakes.

I have replaced the circuit breaker thinking it may be bad and there was no change, so it seems the breaker was ok.

Does my circuit breaker need to be a higher value?

Thanks Mike

[fcel]

Let's start with the fuse first. Did you use slow blow fuse?

[MikeW]

Check for shorts. Disconect the output and check the Mosfets. Make sure Q1,Q2,and Q3 are still good. Check the polarity of the Caps. Make sure all the Zeners are the right way. After checking powering it up at a lower voltage and see if it works. Good luck.

[MikeZ]

fcel: I did not use a slow blow fuse, I used a 4 amp circuit breaker. Do you think the circuit breaker is faster than the slow blow fuse? If so I can try to purchase a slow blow fuse.

mikew: I disconnected my main board from the output boards which have the fets mounted on them, there were no shorts on the main board. cap polarity is correct, zeners mounted correct. I do not have equipment needed to test the fets, I purchased matched sets off this forum so I am assuming they are good.

[Andypairo]

I'd start with a light bulb in series with the primary (or a variac), in order to operate the amp with substantially lower voltage (and without tripping the breaker), and then I'd look for what's wrong.

Cheers

Andrea

[macka]

Mike,

This is all part of diy, but here are a couple of possible clues.

1. Your mains voltage is about 120 VAC right?

Well the draw on the Aleph is about 300 watts, but your amp could well be drawing more than this as the rail voltages of your amp are 6 volts over the design of 45volts DC and I'm not sure if you are using a thermister for the soft start up . This may have the effect of causing the breaker to trip near its "Threshold" (sorry about, I could not resist the Pun...I can hear Mr Pass chuckling).

The solution for the above hypothesis is to replace / bypass the breaker for a proper 4 amp slow blow fuse as per the design and also make sure you are using the Keystone CL 60 Thermister for a soft start.

2. If this does not work, check the value of R19, it should be 56k, this resister trims the DC bias to 3 amps.

Then check the voltage across Q5 to ensure the CCS is working okay as per the schematic with the outptut fets isolated from the supply rails temporarily. The bias level also can be lowered / raised trimming the value of R19.

Note that correct the bias is with about 0.50 volt across the 1.0 ohm source resistors and the dissipation of the output fets will be a shade high with your supply rails of 51 volts but not enough to loose sleep over!

3. If this does not work check the output stage Fets G D S to ensure you have the wiring okay with the schematic, note only one fet source is connected to the sense return wire per side.

Then check the voltages on the driver board as per the schematic, again with the output stage isolated from the DC rails.

Hope this works...good luck.

macka

[nbaula]

Hi! MikeZ did you find out what the problem is?

[MikeZ]

I have not had a chance to work on it, living in a small town, I have to order everything by mail. I have ordered fuse holder and slo blo fuses. I am hoping it comes today and I can test over the weekend. I will post results after testing the fuses.
Thanks Mike

[MikeZ]

Update, Put in 4a slo blo fuse it blew. Put in 5a slo blo fuse and it took a bit longer to blow but not long enough to take any measurements.

Cap polarity is correct, zener polarity is correct. I checked for shorts and couldnt find any, I performed this check with multimeter and most items gave me some resistance. Couldn't check the fets as I didnt know how. How can I check the fets to see if they are good?

Mains voltage is about 120 VAC. I am using a Keystone CL 60 Thermister for a soft start. R19 is 56.2K. Can't check the voltage across Q5 as the amp shuts down too quick. Only one fet source is connected to the sense return wire per side. To check the voltages on the driver board as per the schematic, with the output stage isolated from the DC rails, do I remove all 12 fets?. If I remove all 12 fets the fuse does not blow, the LED does not function.

As I stated If all 12 FETS are removed the fuse doesnt blow. Should I be able to check voltage drops across most components then?

Any advice?

[MikeZ]

one more thing, what does CCS stand for. Thanks Mike