Adjusting both doesn't make a difference that I can tell. The other channel biases up just fine (accept needing more r at r3&4).
Possibly a bad trimpot or bad resistor somewhere?
Possibly a bad trimpot or bad resistor somewhere?
Adjusting both is how you get your DC offset to go to zero -- and that is hugely important in this amp.
The trick is to get things to .2v bias or thereabout and zero the offset.
Then increase the bias to .4, and zero the offset - you will notice that one ill effect the other, so it's always two steps forward and one step back - that's normal.
go to .5, zero the offset, and then set .6, and zero the offset again.
Also you need to have the thermistors on the amp PCB touching the plastic body of the power mosfet, that way they can track the temperature properly.
The trick is to get things to .2v bias or thereabout and zero the offset.
Then increase the bias to .4, and zero the offset - you will notice that one ill effect the other, so it's always two steps forward and one step back - that's normal.
go to .5, zero the offset, and then set .6, and zero the offset again.
Also you need to have the thermistors on the amp PCB touching the plastic body of the power mosfet, that way they can track the temperature properly.
Ok, I got a couple minutes to work on the amp last night.
My broken channel seems to be in worse shape than last time. I no longer measure any voltage across r12. With the pots fully open I measure .015 Volts across r11. I also noted that with 30 minutes of warm up, the heat sink was still very cool, whereas the 'functioning' channel biased to .36 was slightly warm.
My broken channel seems to be in worse shape than last time. I no longer measure any voltage across r12. With the pots fully open I measure .015 Volts across r11. I also noted that with 30 minutes of warm up, the heat sink was still very cool, whereas the 'functioning' channel biased to .36 was slightly warm.
any thoughts here guys (gals)?
With no Voltage across r12, I am assuming there is a short somewhere prior to that resistor. Is this correct and how do I trace the bad component?
I saw f5v3 boards were posted to the store. Is it time to start over? I hope not. I won't learn anything that way....
With no Voltage across r12, I am assuming there is a short somewhere prior to that resistor. Is this correct and how do I trace the bad component?
I saw f5v3 boards were posted to the store. Is it time to start over? I hope not. I won't learn anything that way....
Don't worry about the F5v3 boards.
With the amp powered off, measure resistances from pin to pin on the Jfets and Mosfets. (Pin 1 to pin 2, pin 2 - 3, pin 1 - 3, etc...) Compare to the good channel. Report any gross variances.
Another thought - di you have the proper device properly inserted in the limiter circuit? (ZTX transistor?)
With the amp powered off, measure resistances from pin to pin on the Jfets and Mosfets. (Pin 1 to pin 2, pin 2 - 3, pin 1 - 3, etc...) Compare to the good channel. Report any gross variances.
Another thought - di you have the proper device properly inserted in the limiter circuit? (ZTX transistor?)
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JIm's (6L6's...) comment above is right on the mark. I just posted this on another F-5 thread, but it applies to your case, as well:
If you know you still have one GOOD channel, and suspect you have successfully repaired the bad channel--I'd take some "comparison" resistance checks WITHOUT APPLYING power as your first remediation step. You already have your two most available tools for troubleshooting--a good channel, and a DMM. Check resistances. If you have repaired the board, such comparison checks can give you a good indication of other bad parts, to include resistors, pots, capacitors, semis, and the occasional PCB short or open.
(In your case, it sounds as though you have one known good channel, and one known bad channel.... The advice is still the same--take comparative measurements, and let us know what you find.... In some cases, it might be worthwhile to unsolder a component (same one, on BOTH boards) to take measurements to isolate the bad actors. Yes, throubleshooting is NOT for the faint of heart.... 🙂 )
If you know you still have one GOOD channel, and suspect you have successfully repaired the bad channel--I'd take some "comparison" resistance checks WITHOUT APPLYING power as your first remediation step. You already have your two most available tools for troubleshooting--a good channel, and a DMM. Check resistances. If you have repaired the board, such comparison checks can give you a good indication of other bad parts, to include resistors, pots, capacitors, semis, and the occasional PCB short or open.
(In your case, it sounds as though you have one known good channel, and one known bad channel.... The advice is still the same--take comparative measurements, and let us know what you find.... In some cases, it might be worthwhile to unsolder a component (same one, on BOTH boards) to take measurements to isolate the bad actors. Yes, throubleshooting is NOT for the faint of heart.... 🙂 )
After quite a bit of time off to get ready for my first children arriving next week (twins!) I found some time for measurements. Everything seems to line up pretty well. I am more stuck than ever.
Q1a SG 99.7K Q1b SG 99.7K
SD 41.1 SD 42.1
GD 99.9K GD 99.8K
Q2a SG 99.8K Q2b SG 99.7K
SD 41.1 SD 38.4
GD 99.9k GD 99.9k
Q3a GD 117 Q3b GD 118.3
Q4a GD 117 Q4b GD 121
Q5a BE 129.5 Q5b GD 129
Q6a BE 129 Q6b GD 128.5
What's my next step guys? Cheers!
Q1a SG 99.7K Q1b SG 99.7K
SD 41.1 SD 42.1
GD 99.9K GD 99.8K
Q2a SG 99.8K Q2b SG 99.7K
SD 41.1 SD 38.4
GD 99.9k GD 99.9k
Q3a GD 117 Q3b GD 118.3
Q4a GD 117 Q4b GD 121
Q5a BE 129.5 Q5b GD 129
Q6a BE 129 Q6b GD 128.5
What's my next step guys? Cheers!
Just noticed that I mislabeled Q5b & Q6b in the above post. Both measurements are resistance BE.
The fact that my bad channel has not heat generated at Q3 & Q4 should give a hint, no?
The fact that my bad channel has not heat generated at Q3 & Q4 should give a hint, no?
Well yes, there's that! 😉
I would love to get this amp playing before they get here. I have an F4 and Aleph J in the que, too.
Twins? Yes, get something built and working before they arrive. Your DIY time will go to ZERO for at least a year...
But aside from that, Congratualtions!
But aside from that, Congratualtions!
Thanks Joca and Attila!
Does the SLPX153M035E7P3 cap look to be good? I think it is the 15000uf version of the above cap.
Or am I better off with 380LX153M035A022 or 380LX153M035A022?
Does the SLPX153M035E7P3 cap look to be good? I think it is the 15000uf version of the above cap.
Or am I better off with 380LX153M035A022 or 380LX153M035A022?
hi giantstairs,
the united chemicon caps seem better. (less esr & more ripple)
plus higher voltage - meaning longer life.
the united chemicon caps seem better. (less esr & more ripple)
plus higher voltage - meaning longer life.