Hi,
I finished wiring my Zen V4 and I ran into trouble when starting it up.
I tried one channel at a time with a variac and got the same problem.
I fused the transformer at 1.5A and set the bias potentiometer to the maximum value.
I first checked the supply voltage which was correct at 50V.
I then connected one channel to the supply and monitored the voltage drop through R0. This voltage is not supposed to go beyond 0.7V. My problem is that I reach this value only about half way on the variac (corresponding to a power supply voltage around 25V).
This indicates that too much current is being drawn, but I need to find out where.
The PCBs were ordered directly from Passdiy and I don't suspect wiring problems.
I did forget to short the input before doing the test , but I redid the power up with shorted inputs and reached the same result.
I am wondering if this current draw is caused by a damaged component.
Would you have any suggestion as to which component would be most suspect and how I can test it (them)?
Any suggestion is welcome.
Thanks,
Olivier
I finished wiring my Zen V4 and I ran into trouble when starting it up.
I tried one channel at a time with a variac and got the same problem.
I fused the transformer at 1.5A and set the bias potentiometer to the maximum value.
I first checked the supply voltage which was correct at 50V.
I then connected one channel to the supply and monitored the voltage drop through R0. This voltage is not supposed to go beyond 0.7V. My problem is that I reach this value only about half way on the variac (corresponding to a power supply voltage around 25V).
This indicates that too much current is being drawn, but I need to find out where.
The PCBs were ordered directly from Passdiy and I don't suspect wiring problems.
I did forget to short the input before doing the test , but I redid the power up with shorted inputs and reached the same result.
I am wondering if this current draw is caused by a damaged component.
Would you have any suggestion as to which component would be most suspect and how I can test it (them)?
Any suggestion is welcome.
Thanks,
Olivier
Hi,
Thanks for the reply.
I tried increasing the supply voltage yesterday, but the R0 voltage drop kept increasing and blew the fuse (1.5A).
In a past thread someone had a similar problem when Q3 was installed wrong. I don't think I did the same mistake but I will check to be sure.
Could a damaged Q3 cause this problem?
Thanks,
O.
Thanks for the reply.
I tried increasing the supply voltage yesterday, but the R0 voltage drop kept increasing and blew the fuse (1.5A).
In a past thread someone had a similar problem when Q3 was installed wrong. I don't think I did the same mistake but I will check to be sure.
Could a damaged Q3 cause this problem?
Thanks,
O.
It takes more time to type than to lead you to this nice link:
http://www.uoguelph.ca/~antoon/gadgets/mostest.htm
/Hugo
http://www.uoguelph.ca/~antoon/gadgets/mostest.htm
/Hugo
Hugo,
I just looked at the schematics and the board layout and I think I found the problem.
The outline of Q3 is printed on the board, but I think there is a
mistake and the collector and emitter pins are reversed.
I looked at the manufacturer datasheet and the order of collector-emitter-base relative to the transistor outline (the flat face) does not seem to correspond to the outline on the board.
I will double check tonight, but it would explain the symptomes that I had on my amplifier. I just hope that I didn't damage any part in the process.
Thanks for the help,
Olivier
I just looked at the schematics and the board layout and I think I found the problem.
The outline of Q3 is printed on the board, but I think there is a
mistake and the collector and emitter pins are reversed.
I looked at the manufacturer datasheet and the order of collector-emitter-base relative to the transistor outline (the flat face) does not seem to correspond to the outline on the board.
I will double check tonight, but it would explain the symptomes that I had on my amplifier. I just hope that I didn't damage any part in the process.
Thanks for the help,
Olivier
Well, I checked again and there is no error in the schematics or the layout.
I checked all my wiring and board stuffing without finding any problem.
The only thing I can imagine is that some transistors are blown.
I will order spare parts and change all of them.
I cannot find anything else right now.
O.
I checked all my wiring and board stuffing without finding any problem.
The only thing I can imagine is that some transistors are blown.
I will order spare parts and change all of them.
I cannot find anything else right now.
O.
I bet it is simple, but the wierd thing is that it happened on both channels and since the PCBs are from PassDIY, the problem is not from the PCB.
It means that I probably made the same mistake twice, but I cannot find it out yet (kind of weird making the same mistake on two PCBs).
I will check the values of all resistors and check the base-emiter voltage of Q3 with a multimeter tonight.
I am pretty sure Q1 and Q2 are dead on one channel and they might have killed R10 in the way.
I have ordered replacement transistors, but I would like to understand why the regulation of Q2 doesn't work when I bring the power up.
A friend was wondering if bringing the power voltage too slow might
damage Q1 when Q2 is not yet regulated. Q1 being dead could cause the death of Q2 and R10.
O.
It means that I probably made the same mistake twice, but I cannot find it out yet (kind of weird making the same mistake on two PCBs).
I will check the values of all resistors and check the base-emiter voltage of Q3 with a multimeter tonight.
I am pretty sure Q1 and Q2 are dead on one channel and they might have killed R10 in the way.
I have ordered replacement transistors, but I would like to understand why the regulation of Q2 doesn't work when I bring the power up.
A friend was wondering if bringing the power voltage too slow might
damage Q1 when Q2 is not yet regulated. Q1 being dead could cause the death of Q2 and R10.
O.
This is turning into a blog, but it is fine, I am sure some will find it interesting.
Here is the damage report from last night's tests.
Right channel:
Q3 junction still good (0.66V)
looks like Q1 is dead (gate-source junction is conductive)
Q2 probably dead
Left channel: Q3 still good (holds 0.66V under power)
Q1 good: I get 4V between source and gate when I bring power up
Q2 probably dead: voltage between R0/R1 rises above 0.66V during power up.
I tested all values of all resistors on both boards (all fine).
All caps seem fine.
Wiring seems fine.
No shorts found.
The only explanation I can come up with is that Q2 transistors got damaged (electrostatic discharge?) before they were installed or that they were blown when I tested the amp without sorting the inputs (oscillations?)
I will get my replacement parts Friday and continue my "detective work".
O.
Here is the damage report from last night's tests.
Right channel:
Q3 junction still good (0.66V)
looks like Q1 is dead (gate-source junction is conductive)
Q2 probably dead
Left channel: Q3 still good (holds 0.66V under power)
Q1 good: I get 4V between source and gate when I bring power up
Q2 probably dead: voltage between R0/R1 rises above 0.66V during power up.
I tested all values of all resistors on both boards (all fine).
All caps seem fine.
Wiring seems fine.
No shorts found.
The only explanation I can come up with is that Q2 transistors got damaged (electrostatic discharge?) before they were installed or that they were blown when I tested the amp without sorting the inputs (oscillations?)
I will get my replacement parts Friday and continue my "detective work".
O.
I finally replaced all faulty transsitors and I get the follwing behavior:
I can monitor the voltage through R0/R1 and it reaches 0.66V when the voltage on the transformer primary is about 90V. The regulated voltage is then about 42V.
If I go any higher the voltage across R0/R1 increases and Q2, Q1 and the fuse all blow.
This behavior is similar on both channels.
- the base-emiter voltage across Q3 and it is fine at 0.66V.
- the source-gate voltage on Q2 and Q1 is 4V
Where could this power be going?
Do you have any suggestion?
Thanks,
Olivier
I can monitor the voltage through R0/R1 and it reaches 0.66V when the voltage on the transformer primary is about 90V. The regulated voltage is then about 42V.
If I go any higher the voltage across R0/R1 increases and Q2, Q1 and the fuse all blow.
This behavior is similar on both channels.
- the base-emiter voltage across Q3 and it is fine at 0.66V.
- the source-gate voltage on Q2 and Q1 is 4V
Where could this power be going?
Do you have any suggestion?
Thanks,
Olivier
Check (condition, pin-out, etc.) all semiconductors -transistors, zeners, diodes...they're usually the first to go. Since the Zen is a simple circuit and you have all the time in the world, might as well check all components plus solders. Concentrate on one channel. Once you nail the first the second will be a breeze.
Don't get frustrated. Keep the dectective work fun.
Don't get frustrated. Keep the dectective work fun.
As far as I understand, the problem with my amplifier is that Q2 is not regulated.
Either Q3 is not doing its job or there is a wiring or part problem in the regulation loop.
Or it may be Q1 not functionning properly, conducting too much and drawing too much current from Q2.
The problem seems to be consistent on both channels and I haven't found it yet.
O.
Either Q3 is not doing its job or there is a wiring or part problem in the regulation loop.
Or it may be Q1 not functionning properly, conducting too much and drawing too much current from Q2.
The problem seems to be consistent on both channels and I haven't found it yet.
O.
Hi all,
I think I found my problem.
It was a tricky one. I brought one of my channel to work and we tested it using a large aluminum plate as heat sink and monitoring several voltages.
Everything went perfectly.
The problem I had was with my heat transfer (I still have to get it to work in my chassis, but I have less doubts now).
Eventhough I have 3 massive heat sinks per channel, the thermal coupling between the transistors and the sinks (aluminum plate) was not as good as I thought. As a consequence Q2 was probably heating up very fast and Q3 couldn't regulate.
I will mount each transistor directly on its own sink and everything should work just as well as in the lab.
Thank you all for your advice, I will keep you updated and I will post some pictures when it is finished.
Olivier
I think I found my problem.
It was a tricky one. I brought one of my channel to work and we tested it using a large aluminum plate as heat sink and monitoring several voltages.
Everything went perfectly.
The problem I had was with my heat transfer (I still have to get it to work in my chassis, but I have less doubts now).
Eventhough I have 3 massive heat sinks per channel, the thermal coupling between the transistors and the sinks (aluminum plate) was not as good as I thought. As a consequence Q2 was probably heating up very fast and Q3 couldn't regulate.
I will mount each transistor directly on its own sink and everything should work just as well as in the lab.
Thank you all for your advice, I will keep you updated and I will post some pictures when it is finished.
Olivier
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