I've been doing some sorting out of my one F5 amp -- I have 4x amp boards to bi-amp my mutt speakers. One of the rectifier bridges packed up, so I got new ones, got some heatskinks for them and did some prettifying.
So far so good, everything back up and running. I noticed a bit of hum from both channels, so decided to do some hum squishing. One thing was to re-adjust bias.
When I built the boards up, I didn't pay attention to which way around the trim pots were, as the casing was not in the way. Now it is... 3 of the 4 trim pots are facing the wrong way to get a screwdriver to.
No worries - unscrew the boards, unsolder the pots and turn them around. Did the left side, reset the bias, all good.
The right side showed no voltage across the R11/R12. Hm, weird I think. Also, full 24V across source & gate (should be 3-4v??) on both MOSFETs.
Hm, thinks I, maybe a bad solder when I put them back. Pull them off again, check, clean up, put back.
Now the moment I power it up, R11 and R12 (the 3W 0R47) start to smoke. Instant smoke, and then fuse goes.
Any ideas? There is no load connected, so the only route to ground is through a bunch of stuff. The output MOSFETs don't get noticeably hotter (although there is little time). Mystified how an accidental soldering prob could affect both halves. If the MOSFETS are fried and shorted, you'd only get 1/2A through R11, so 1/8W. Where do I even start?
So far so good, everything back up and running. I noticed a bit of hum from both channels, so decided to do some hum squishing. One thing was to re-adjust bias.
When I built the boards up, I didn't pay attention to which way around the trim pots were, as the casing was not in the way. Now it is... 3 of the 4 trim pots are facing the wrong way to get a screwdriver to.
No worries - unscrew the boards, unsolder the pots and turn them around. Did the left side, reset the bias, all good.
The right side showed no voltage across the R11/R12. Hm, weird I think. Also, full 24V across source & gate (should be 3-4v??) on both MOSFETs.
Hm, thinks I, maybe a bad solder when I put them back. Pull them off again, check, clean up, put back.
Now the moment I power it up, R11 and R12 (the 3W 0R47) start to smoke. Instant smoke, and then fuse goes.
Any ideas? There is no load connected, so the only route to ground is through a bunch of stuff. The output MOSFETs don't get noticeably hotter (although there is little time). Mystified how an accidental soldering prob could affect both halves. If the MOSFETS are fried and shorted, you'd only get 1/2A through R11, so 1/8W. Where do I even start?
