First off, many thanks to 6l6. And what a great community this is..
I’ve been working on my first amp build, an F5, and thought tonight was going to be the night. With your help, I was able to get 1 board biased up and figured the 2nd would be a piece of cake.
Had my voltmeter on output resistor and start to open up the potentiometer but didn’t see any increase in voltage, and I spun it open for a while. Moved over to the other pot and started to make some turns and saw some voltage across the resistor quickly.
Then I started checking voltages on some of the resistors so that I could compare to the other board that was up and running at full bias. I was reading 0.7V on resistors R9, R10, R11, R12 on the fulyl biases board, but 0.35 V on the same resistors.
Starting to wonder if I have a cold solder joint on one of my power inputs to the board. Voltages at the output of the PSU caps check out.
Any and all help and suggestions are greatly appreciated.
Thanks
I’ve been working on my first amp build, an F5, and thought tonight was going to be the night. With your help, I was able to get 1 board biased up and figured the 2nd would be a piece of cake.
Had my voltmeter on output resistor and start to open up the potentiometer but didn’t see any increase in voltage, and I spun it open for a while. Moved over to the other pot and started to make some turns and saw some voltage across the resistor quickly.
Then I started checking voltages on some of the resistors so that I could compare to the other board that was up and running at full bias. I was reading 0.7V on resistors R9, R10, R11, R12 on the fulyl biases board, but 0.35 V on the same resistors.
Starting to wonder if I have a cold solder joint on one of my power inputs to the board. Voltages at the output of the PSU caps check out.
Any and all help and suggestions are greatly appreciated.
Thanks
Hi Dennis. I’ve measured the voltage at the inputs of the PCB, inconclusively. I say that because i have heat shrink tubing down to the base of the PCB making it tough to get a reading. Without a doubt, I’ve had the lead on bits of the solder on top of the PCB and got no reading.....and other bits I’ve got a reading of 25v. When checking voltage by placing my lead on the cable on the backside of the board, clearly 25v.
All of this I’ve described is specific to one side (either +/-....can’t remember which), the other side is clearly fine.
The offset is .04 volts. As soon as I start the bias process and open up the potentiometer to where I start to see voltage at the resistor, the offset increases dramatically (1.4mV at resistor, 0.116V offset).....and there is nothing I can do to the opposing pot to start seeing voltage in the resistor.
Any thoughts?
All of this I’ve described is specific to one side (either +/-....can’t remember which), the other side is clearly fine.
The offset is .04 volts. As soon as I start the bias process and open up the potentiometer to where I start to see voltage at the resistor, the offset increases dramatically (1.4mV at resistor, 0.116V offset).....and there is nothing I can do to the opposing pot to start seeing voltage in the resistor.
Any thoughts?
On the bad board, can you access the bottom to verify you have proper +/- voltages?
If they look suspect then reflow the soldering.
Assuming the input voltages are ok, referring to schematics on Page 2 here:
http://www.firstwatt.com/pdf/art_f5_turbo.pdf
what voltage are you getting across R5 and R6? And when you adjust the pots P1
and P2, do the voltages change? If one changes and not the other, which one
doesn't change?
If they look suspect then reflow the soldering.
Assuming the input voltages are ok, referring to schematics on Page 2 here:
http://www.firstwatt.com/pdf/art_f5_turbo.pdf
what voltage are you getting across R5 and R6? And when you adjust the pots P1
and P2, do the voltages change? If one changes and not the other, which one
doesn't change?
So,-23 volt where R6 meets the negative rail?
What voltages do you see across R5 and R6 as you adjust P1 and P2? What is
the max voltage you see across R5 and R6 as you adjust the pots? (Do it one
at a time) We need to see if it's simply a matter of not having adequate voltage
there to turn on the mosfets.
What voltages do you see across R3 and R4?
Where did you get your jfets? Do you know the Idss of the jfets?
What voltages do you see across R5 and R6 as you adjust P1 and P2? What is
the max voltage you see across R5 and R6 as you adjust the pots? (Do it one
at a time) We need to see if it's simply a matter of not having adequate voltage
there to turn on the mosfets.
What voltages do you see across R3 and R4?
Where did you get your jfets? Do you know the Idss of the jfets?
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Appreciate the help guys.
I'll follow up with the R3/R4 voltages before I take the board of the heat sinks and check for suspect soldering. I had done a quick visual on the top of the boards, but didn't know if the various voltages readings in place would validate where/if I had any soldering issues. (Sounds like that's the likely culprit)
I don't know the Idss of the jfets, but I bought them from the diayaudiostore
Path forward, I'll take some more readings, pull the boards off and re-flow. Then what? specifically, is there anything else to do while I have the boards of the heat sinks? Should I power up with the pots turned all the way down and run some checks, or do I need to mount to sinks first?
Thanks,
I'll follow up with the R3/R4 voltages before I take the board of the heat sinks and check for suspect soldering. I had done a quick visual on the top of the boards, but didn't know if the various voltages readings in place would validate where/if I had any soldering issues. (Sounds like that's the likely culprit)
I don't know the Idss of the jfets, but I bought them from the diayaudiostore
Path forward, I'll take some more readings, pull the boards off and re-flow. Then what? specifically, is there anything else to do while I have the boards of the heat sinks? Should I power up with the pots turned all the way down and run some checks, or do I need to mount to sinks first?
Thanks,
Thanks Dennis,
6L6 brought to my attention that I had ztx550 in backwards. I de-soldered and replaced with a new. But unfortunately, all is the same.
I've gone ahead and taken voltage readings on all the resistors in the attached spreadsheet.
Not sure what else to do. I actually have mosfets on hand, but don't know if I should swap out, or try another troubleshooting tactic.
readings taken with the pots turned down fully, where you'd start the bias process.
I also took readings to the leads of the mosfets, 23.5 as well
Really appreciate the help. I'm so excited to hear the music
6L6 brought to my attention that I had ztx550 in backwards. I de-soldered and replaced with a new. But unfortunately, all is the same.
I've gone ahead and taken voltage readings on all the resistors in the attached spreadsheet.
Not sure what else to do. I actually have mosfets on hand, but don't know if I should swap out, or try another troubleshooting tactic.
readings taken with the pots turned down fully, where you'd start the bias process.
I also took readings to the leads of the mosfets, 23.5 as well
Really appreciate the help. I'm so excited to hear the music
Solved - Sounds Amazing!
Here were my two issues: I had ztx550 flipped in orientation and I accidentally clipped the leg of one of the JFets. Feel like a bonehead, both things easily preventable and I should caught the mistakes. But man am I thankful for the help from Dennis and 6L6.
This was quite a learning experience. I had a blast. And the music....holy cow, the thing sounds amazing. Thanks diyAudio!
Here were my two issues: I had ztx550 flipped in orientation and I accidentally clipped the leg of one of the JFets. Feel like a bonehead, both things easily preventable and I should caught the mistakes. But man am I thankful for the help from Dennis and 6L6.
This was quite a learning experience. I had a blast. And the music....holy cow, the thing sounds amazing. Thanks diyAudio!
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