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gionag 18th May 2008 07:34 PM

Little (or big ?) problem with a Zen V9.
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Hi guys !

i came back with another issue...
i finished yesterday my Zen V9 based on the pcb of PD & DA.

The power supply is formed by a 300VA toroid with a 240 pri and a 0-36V sec.
After that, i used only 10.000uf 160V cap for filtering (waiting the array of new caps).

I temporaney put the Q2-Q3-Q4 (the 3 irfp240) on a single heatsink (10x23x5cm) and the Lu1014 on a separate one.

The first test was a disaster, one mosfet smoked for over heating ( i was wrong with the assemblage and only a little part of the mosfet surface was in contact with heatsink ). Fixed the assembly of mosfet i tried again powering up the device... and with P1 totally closed i've 39Volt on the drain of Q2. on Q3 i have (between it's drain and GND) 43volt. with P1 i have to set the voltage between Drain of Q2 and GDN at about one-half of 43volt (21.5volts) but........

When i'm going to set the voltage on P1 i can't reach the 21.5volts on the Drain of Q2 and when i'm going just a little under 39volt the array of 2ohm resistors (R1-R2-R3) became so hotter... but very, very, very hot...

the temperature on the heatsinks is fine and the mosfets aren't so hot.

What can happened ? Probably i broke some components...
What points i've to measure for checking if anything is ok ?

thanks for support.
(i understand my incorrect way of expressing facts, if you have any question ask me for more information and i'll try to answer !)

:D bye bye

gionag 18th May 2008 07:42 PM

Voltages measured during tests :

Drain To GND ON Q4 = 50.6Volt
Drain to GND ON Q3 = 43.7Volt

What other measurement can help you ?

gionag 19th May 2008 11:32 AM

maybve there is something in my post that you don't understand ? i'm not a wizard in english :D

Nelson Pass 19th May 2008 06:41 PM

I suggest that you report all pin voltages of all transistors.

The overheating of the resistors suggests that Q3 is being
biased to a higher current than you want.

gionag 19th May 2008 06:52 PM

so, I'll check each voltage between each pin and GND..

stay tuned...

gionag 19th May 2008 06:54 PM


Originally posted by Nelson Pass
I suggest that you report all pin voltages of all transistors.

The overheating of the resistors suggests that Q3 is being
biased to a higher current than you want.

which is the part of circuit that bias Q3 ? excuse me but i am not an engineer... :D

and... why the resistors became so hot only when i lower the voltage on drain Q3 ?

Nelson Pass 20th May 2008 07:24 PM

It's the part attached to the Gate of Q3.

gionag 20th May 2008 11:10 PM

ok... tonight i've desoldered everything and i tryed to rebuild from zero the whole pcb.

i Only kept one "old" mosfet, and the bypass cap of the output cap (C7) and the Bc637 (in place of ZTX450).

few seconds after turning on device, the toroid emits a noise like a "fuzz"... as you hear when you pass near an electrical forniture.

and i was unable to adjust voltages trough P1 and i smoked the 3 2.0ohm resistors.

the only things that is different from pass original design is the Bc637 instead ZTX450 (Q5).

as suggested mr.pass maybe i fault the section that's bias Q3, and there is the Q5...

can different parts is the guilty of these problems ? bc637 seem to be a good equivalent.
And what about "Fuzz" of toroid ?

what other parts of circuit that i can check ?

I'm so sad... :whazzat: :whazzat: :whazzat:

I can't measure voltages across Mosfet because the amp smoke after 9-10 seconds of startup.


Magura 20th May 2008 11:26 PM

I would start out by checking all the components are still alive and well.
Check the pinout of all the three legged fellas, are they mounted correct? compare the PCB with the schematic, and your components.

Magura :)

gionag 20th May 2008 11:30 PM

i already swapped the pins of the bc637 because Ztx450 has different pin-out. that is ok...
and i'm sure that the mosfets is ok.

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