So I found an older mosfet amp that largely resembles a Hafler DH500, but without output protection, slightly lower rail voltage.
When I got inside, I quickly noticed that the zobel resistors were burnt open, well, almost open.
After replacing some output decoupling .1uf, and the electrolytic rail decoupling for the driver/predriver stage, as well as the resistors, I fired it up, noticed that one channel is slightly distorted, and clips fairly easily. The dc offset is stable, and the same on both channels.
If I had a scope here, I would be better off, but may just swap the driver boards side to side and see if by chance the outputs are bad, unlikely, but possible after being run in oscillation for long enough to barbeque the resistors possibly so(?)
I used some small package 3watt wirewound resistors in the zobel, since I had them here, but am thinking that might not be the best choice, and will have to get some metal film parts to try before any transistors.
Any thoughts on this one?
When I got inside, I quickly noticed that the zobel resistors were burnt open, well, almost open.
After replacing some output decoupling .1uf, and the electrolytic rail decoupling for the driver/predriver stage, as well as the resistors, I fired it up, noticed that one channel is slightly distorted, and clips fairly easily. The dc offset is stable, and the same on both channels.
If I had a scope here, I would be better off, but may just swap the driver boards side to side and see if by chance the outputs are bad, unlikely, but possible after being run in oscillation for long enough to barbeque the resistors possibly so(?)
I used some small package 3watt wirewound resistors in the zobel, since I had them here, but am thinking that might not be the best choice, and will have to get some metal film parts to try before any transistors.
Any thoughts on this one?
Hi phase,
I wouldn't swap the boards if I were you. Not having a scope also means not knowing what's going on in there. Swapping the boards is a newbie mistake, and you know that.
So, if you swap the boards and the trouble follows the board, you might be lucky and still have a good board. If the trouble stays on that channel, and follows the defective board you may have the worst case. Another damaged channel while not being any further ahead to know what is wrong.
To be honest, you might be further ahead to yank the "bad" driver board and simply check every semi-junction with your meter. That will tell you much more than swapping things around ever will. That and there isn't a risk of blowing up good parts.
-Chris
I wouldn't swap the boards if I were you. Not having a scope also means not knowing what's going on in there. Swapping the boards is a newbie mistake, and you know that.
So, if you swap the boards and the trouble follows the board, you might be lucky and still have a good board. If the trouble stays on that channel, and follows the defective board you may have the worst case. Another damaged channel while not being any further ahead to know what is wrong.
To be honest, you might be further ahead to yank the "bad" driver board and simply check every semi-junction with your meter. That will tell you much more than swapping things around ever will. That and there isn't a risk of blowing up good parts.
-Chris
Thanks Chris, I will resist the urge to swap the boards; bad one is the harder one to access, so that isn't helping things.
One thing I thought of was to take some voltage readings on the good side, to see if maybe any diodes are leaky.
The drivers are still available, just not cheap.
Thanks again. More probing around here when I get a chance...
One thing I thought of was to take some voltage readings on the good side, to see if maybe any diodes are leaky.
The drivers are still available, just not cheap.
Thanks again. More probing around here when I get a chance...
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