merlin , your brother is wrong . you must zero both pots by measuring across r3 and r4 ! cw and ccw mean nothing . as ZM told you it all depends on the board design , the pots and the way you installed them .
cheers Woody
cheers Woody
Ok, I knew he was wrong.
When you have them both pots set to ~ "0", isn't one mosfet on and the other off? Will you see .00v at R11 & R12 or just one of them?
Or replace the pots with photocells......that way, sometime during the day or night, the bias will set itself properly....for a few minutes.....
(Actually, I keep a little 3 x 5 file card in my folder with my F5 notes, BOM, schematics, etc...... just to remind me in which direction to tweak my pots, whenever I go in to fine-tune my bias settings....)
Ok, something is out of wack. When I've got both pots at "0", I've got R11 @ .35v and R12 @ .0v (or vise versa).
I've think I've gone over the circuit carefully, I can't account for the offset.
Any suggestions?
To develop a voltage across a resistor, there must be current flow, where does the current exit the circuit? .35V/.47R=0.74465A
Begin by fitting a shorting link directly across the gate/source of the FET with the .35V. If the voltage remains, there is a either a current path through the source/tab/heatsink or via R17/18 or R13/14. If it's R13/14 the FET is duff.
Thanks. I've ordered a couple of extra mosfets (irfp9240 /irfp240), the 22k ohm that I replaced with 10k ohm, and some 5k trimmers.
Hopefully, I'll get the problem solved.
Hopefully, I'll get the problem solved.
Arg, still having problems with my amp.
I've replaced 2x 5k trim pots, I've put back in the 22k ohm that I mistakenly removed.
I've zeroed the pots (turned them fully counter clockwise -checked r3 + r4 too), re-attached everything again.
When I powered it up my fuse popped and blackens my R11 + R12 resistors.
Any suggestions?
I've replaced 2x 5k trim pots, I've put back in the 22k ohm that I mistakenly removed.
I've zeroed the pots (turned them fully counter clockwise -checked r3 + r4 too), re-attached everything again.
When I powered it up my fuse popped and blackens my R11 + R12 resistors.
Any suggestions?
I think I shorted one of the mosfets.
The next time I started it up it smoked my R13 (47ohm) resistor.
I've got replacement mosfets, but no r13 spare.
Can anyone spare a couple of 47ohm 1/4 1% resistors?
The next time I started it up it smoked my R13 (47ohm) resistor.
I've got replacement mosfets, but no r13 spare.
Can anyone spare a couple of 47ohm 1/4 1% resistors?
Arcol Resistors - RS Components Canada
Lol I also fried a fet for the first time, Saturday, Tried to measure rail with DMM set to temperature mode... When you care more about your speakers than your amp, you rip that speaker cable out like it was a snake attacking your kittens. 🙂 No harm done though
Lol I also fried a fet for the first time, Saturday, Tried to measure rail with DMM set to temperature mode... When you care more about your speakers than your amp, you rip that speaker cable out like it was a snake attacking your kittens. 🙂 No harm done though
Hi JC,
I'm not Albertob, but if you're looking for heatsinks you might be interested
FRANAB - Industria Metalúrgica Ltda
If you're in SP then they're in your neighbourhood. I bought sinks from them for my F5 a year or two ago and was very pleased the quality of the sinks and the service. I live in Brasilia, so probably like you I can't buy sinks from the places most people on the forum do, because of the shipping cost, but these came out quite reasonably priced.
Regards
Nigel
irfp9240
I pulled it out of my system, along with the fried R13 (47ohm 1/4 watt resistor).
And between gate & drain I read 23ohms -- I guess that's bad, because the new one is OL between gate & drain.
Hopefully nothing else is wrong with the unit. I'm going to mount the new one and try biasing it up again.
I pulled it out of my system, along with the fried R13 (47ohm 1/4 watt resistor).
And between gate & drain I read 23ohms -- I guess that's bad, because the new one is OL between gate & drain.
Hopefully nothing else is wrong with the unit. I'm going to mount the new one and try biasing it up again.