Hi!
I've had my two F5 builds with dual mono, CLC PSU up and running for about two years now.
Over the last weeks I started noticing two issues with one of the channels on one amp. I first noticed that the LED was using a lot more time to stop glowing after power down than on the other channel. I then noticed a lot more "pop" on that channel at startup.
So, I decided to adjust the bias. I removed the cover, attached all three mulitmeters at the right places and startet up. Nearly 1.8VDC at the output and 4mV\14mV over the resistors.
When trying to adjust the bias, I can get the voltage over the output down to 0 by adjusting one of the potentiometers, but the other one does not respond at all.
After a visual inspection I can see some traces of heat over Q1 and Q2, but I'm not positively sure that its new since they were soldered in and out a few times during the building.
Where do I start?
I've had my two F5 builds with dual mono, CLC PSU up and running for about two years now.
Over the last weeks I started noticing two issues with one of the channels on one amp. I first noticed that the LED was using a lot more time to stop glowing after power down than on the other channel. I then noticed a lot more "pop" on that channel at startup.
So, I decided to adjust the bias. I removed the cover, attached all three mulitmeters at the right places and startet up. Nearly 1.8VDC at the output and 4mV\14mV over the resistors.
When trying to adjust the bias, I can get the voltage over the output down to 0 by adjusting one of the potentiometers, but the other one does not respond at all.
After a visual inspection I can see some traces of heat over Q1 and Q2, but I'm not positively sure that its new since they were soldered in and out a few times during the building.
Where do I start?
having functional channel , it's easy to compare
check resistors , traces , best to replace trimpots
it's best to remove JFets and check them in matching jig
pull one leg of mosfet source resistors and check them
check mosfet screws tightness , check for possibly continuity between them and heatsink
it's easy ...... considering ziliion of parts involved
check resistors , traces , best to replace trimpots
it's best to remove JFets and check them in matching jig
pull one leg of mosfet source resistors and check them
check mosfet screws tightness , check for possibly continuity between them and heatsink
it's easy ...... considering ziliion of parts involved
R2 looked a bit weird, so I replaced it. Measured OK out of the PCB.
Pulled one leg of both mosfet source resistors, both OK.
Screw tightness and continuity for mosfets were good.
Visual checks ok, can't find anything wrong when I try to measure points on the functioning side vs the faulty side, but I can't really say that I know what I am looking for....
Tried to turn P1 and P2 all the way down for a new bias adjust. Nothing happens when turning P1. P2 reacts after about three turns.
Any tips on what to do next?
Pulled one leg of both mosfet source resistors, both OK.
Screw tightness and continuity for mosfets were good.
Visual checks ok, can't find anything wrong when I try to measure points on the functioning side vs the faulty side, but I can't really say that I know what I am looking for....
Tried to turn P1 and P2 all the way down for a new bias adjust. Nothing happens when turning P1. P2 reacts after about three turns.
Any tips on what to do next?
Failed to mention in the intro that the amp played music when I saw that the initial errors, and that I also noticed that it was not getting hot at all, barely hand temperature.
I have of course not tried to play music on it after I have started the troubleshooting, but my first guess was that the JFets and mosfets were not broken since it was playing music without major problems....?
Will try to check JFets and mosfets asap.
I have of course not tried to play music on it after I have started the troubleshooting, but my first guess was that the JFets and mosfets were not broken since it was playing music without major problems....?
Will try to check JFets and mosfets asap.
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