Hi all, a troubleshooting request here...
After three years in storage and a too-many-steps international moving process I finally have my stereo again and just started reviewing my F4 monoblocks to press them back into service.
Unfortunately one of the amps won't bias up correctly. I was following the procedure and had the bias sitting at .13v for an hour, didn't touch the offset because it was at .06v. I then moved the bias up to .300v and switched over to check the bias, only to find that turning P2 had no effect. After many turns (in both directions), I switched back to look at the offset and saw it reading .750v. I immediately killed the power and started cranking down P1. Now I'm gonna have to find the problem, but unfortunately lack any knowledge of where to start as I'm still at the legos stage.
Some further details...
1. I haven't had the fortitude to turn it back on, but I did notice when I killed the power that the heat sinks were not warm very warm... I thought they were warming up during the initial hour, but I'm running on fumes after trying to put an entire house together for 3 days straight and might have been mistaken. Maybe the mosfets never powered up.
2. I have monoblocks with external power supplies (there's only one channel in each box) and just attached the second amp to the power supply that was already in place from biasing up the first amp. Unfortunately there was still some charge in the capacitors. So it's possible that I fried something right then and there, although I was able to power it up and adjust the bias.
3. I did not smoke anything. No fumes at all throughout the process.
Any thoughts on where to start for troubleshooting would be greatly appreciated. Unfortunately I'm three years out of practice... and like I said, never really made it out of the lego stage back when I was in the thick of it.
Thanks so much folks. I adore these amplifiers and am eternally grateful to the group here for making it all possible.
- Chris
After three years in storage and a too-many-steps international moving process I finally have my stereo again and just started reviewing my F4 monoblocks to press them back into service.
Unfortunately one of the amps won't bias up correctly. I was following the procedure and had the bias sitting at .13v for an hour, didn't touch the offset because it was at .06v. I then moved the bias up to .300v and switched over to check the bias, only to find that turning P2 had no effect. After many turns (in both directions), I switched back to look at the offset and saw it reading .750v. I immediately killed the power and started cranking down P1. Now I'm gonna have to find the problem, but unfortunately lack any knowledge of where to start as I'm still at the legos stage.
Some further details...
1. I haven't had the fortitude to turn it back on, but I did notice when I killed the power that the heat sinks were not warm very warm... I thought they were warming up during the initial hour, but I'm running on fumes after trying to put an entire house together for 3 days straight and might have been mistaken. Maybe the mosfets never powered up.
2. I have monoblocks with external power supplies (there's only one channel in each box) and just attached the second amp to the power supply that was already in place from biasing up the first amp. Unfortunately there was still some charge in the capacitors. So it's possible that I fried something right then and there, although I was able to power it up and adjust the bias.
3. I did not smoke anything. No fumes at all throughout the process.
Any thoughts on where to start for troubleshooting would be greatly appreciated. Unfortunately I'm three years out of practice... and like I said, never really made it out of the lego stage back when I was in the thick of it.
Thanks so much folks. I adore these amplifiers and am eternally grateful to the group here for making it all possible.
- Chris
+ rail = 24.5v
- rail = -25.1v
SR bias (adjusted via R1) = .15v
PMOS_gate (top of R15) - NMOS_gate (top of R11) = 8.5v
Thanks, I meant, measured between the two gates accessing at the gate side resistor legs of R15 and R11. Using standard store boards.
And will work on my terminology. Thanks! Like I said, it's been three years of listing to music through a portable bluetooth, so I'm way out of practice.
So appreciate the help!
And will work on my terminology. Thanks! Like I said, it's been three years of listing to music through a portable bluetooth, so I'm way out of practice.
So appreciate the help!
now, simple logic sez this - if that same amp was proper operative prior to getting it to storage, it would be best to dismantle pcb and inspect all soldering points, redo what is suspicious and even more than just suspicious
taking same care as during initial assembly, put everything back, renewing thermal goo if there is
repeat setting procedure
if problem is solved, that was it
if not, we're going to troubleshoot ......... though - in most cases it's simple as replacing TL431 or just increasing R8 to first standard value or decreasing R9 to first standard value
reason - some TL431 are all equal ........ while some TL431 are even more equal
if your trimpots are common 270deg rotation type - be a Chicken as ZM, replace them with multiturns - much easier life for us not initiated in ABFAB Club
taking same care as during initial assembly, put everything back, renewing thermal goo if there is
repeat setting procedure
if problem is solved, that was it
if not, we're going to troubleshoot ......... though - in most cases it's simple as replacing TL431 or just increasing R8 to first standard value or decreasing R9 to first standard value
reason - some TL431 are all equal ........ while some TL431 are even more equal
if your trimpots are common 270deg rotation type - be a Chicken as ZM, replace them with multiturns - much easier life for us not initiated in ABFAB Club
Agreed. It's heating up normally now. I think I'll repeat what I did yesterday just to see if I get the same result when trying to bias up to .350v, Then dismantle, and follow your advice. I don't want to just be waiting for it to blow one day, it's not so easy (or at least cheap) to get stuff shipped to Panamá. Hopefully all my screws hold up to the torsion.
Thank you!!
Thank you!!
now, simple logic sez this - if that same amp was proper operative prior to getting it to storage, it would be best to dismantle pcb and inspect all soldering points, redo what is suspicious and even more than just suspicious
taking same care as during initial assembly, put everything back, renewing thermal goo if there is
repeat setting procedure
if problem is solved, that was it
if not, we're going to troubleshoot ......... though - in most cases it's simple as replacing TL431 or just increasing R8 to first standard value or decreasing R9 to first standard value
reason - some TL431 are all equal ........ while some TL431 are even more equal
if your trimpots are common 270deg rotation type - be a Chicken as ZM, replace them with multiturns - much easier life for us not initiated in ABFAB Club
So, in your opinion... the most likely thing to go awry with an amplifier after medium term ( 1-2 years ) storage is the trim pots?
I'n curious because I need to learn how to maintain my amps, now that I've built a collection... and I can't be relying on 3rd parties to do this for me.
far from that being a rule
many amps were left for long time and functioned good after flippin' da switch even in cases of some poor soul powered an amp logically needing at least some reconditioning - example - eons old tube amps
my remark was more about us poor amateurs not being brave enough to use single/partial turn trimpots, as Papa is used to
He's Big Boy, doing amps from Betlehem's night, if not even before
now - amp which was left working and now is not, it must be something trivial - any sort of poor contact - be it mechanical or soldered....... if we exclude possibility of caps shot, not enough time for that
luckily - good caps are having half life time much longer
many amps were left for long time and functioned good after flippin' da switch even in cases of some poor soul powered an amp logically needing at least some reconditioning - example - eons old tube amps
my remark was more about us poor amateurs not being brave enough to use single/partial turn trimpots, as Papa is used to
He's Big Boy, doing amps from Betlehem's night, if not even before
now - amp which was left working and now is not, it must be something trivial - any sort of poor contact - be it mechanical or soldered....... if we exclude possibility of caps shot, not enough time for that
luckily - good caps are having half life time much longer
Tube amps are indeed a different issue, but I've had issues with potentiometers getting dirty when not used. Sometimes rotating them a hundred times will clean them, sometimes not. Same with mechanical switches.
I figure a multi turn pot might be easier to clean by rotating it a bit back and forth, keeping track of its initial location, whereas a single turn pot would likely go wildly out of "calibration".
I figure a multi turn pot might be easier to clean by rotating it a bit back and forth, keeping track of its initial location, whereas a single turn pot would likely go wildly out of "calibration".
Using a method found on the internet
http://www.diamondstar.de/transistor_matching_mosfet.html
I tested my diyaudio store bought mosfets and got the following results.
How would you best distribute these p and n channels on four f4 boards (two monoblocs)?
http://www.diamondstar.de/transistor_matching_mosfet.html
I tested my diyaudio store bought mosfets and got the following results.
How would you best distribute these p and n channels on four f4 boards (two monoblocs)?
I know it's not the time for questions, but if someone is willing... I have a problem with adjusting the offset on one channel. The DMM shows no change when spinning. I already changed TL 431 and p2 trimpot - no change. I noticed that the power supply shows a difference of approximately 1.5v between the + and - rails while the channel board is connected to it. When the channel board is disconnected the power supply shows exactly the same voltage on the clothes rail???
