Are you referring to the power supply FETs?
If so, the 3205 is a good sub.
The gate resistors are 10 ohms.
http://www.bcae1.com/temp/IMG_6206b.jpg
You also need to check the MPSA56 driver transistors. There are 2 sets of drivers. One set is near the center of the board. The other set is in a group of capacitors near the transformer.
http://www.bcae1.com/temp/IMG_6207b.jpg
http://www.bcae1.com/temp/IMG_6192b.jpg
If you have 11 burned gate resistors, ALL of the power supply FETs need to be replaced. The gate resistors won't burn unless the FET has failed.
Rockford will provide schematics for amplifiers that are out of production (as long as the circuit isn't still in use in the new amps -- that was the case for the BD amps, anyway).
If so, the 3205 is a good sub.
The gate resistors are 10 ohms.
http://www.bcae1.com/temp/IMG_6206b.jpg
You also need to check the MPSA56 driver transistors. There are 2 sets of drivers. One set is near the center of the board. The other set is in a group of capacitors near the transformer.
http://www.bcae1.com/temp/IMG_6207b.jpg
http://www.bcae1.com/temp/IMG_6192b.jpg
If you have 11 burned gate resistors, ALL of the power supply FETs need to be replaced. The gate resistors won't burn unless the FET has failed.
Rockford will provide schematics for amplifiers that are out of production (as long as the circuit isn't still in use in the new amps -- that was the case for the BD amps, anyway).
I checked the 10 ohm gate resistors. 5 of them read crazy numbers like .682 and 126.5 . Im testing the resistors off the board. So im assuming theese are bad. Should i replace all of the gate resistors in the amp ? the other resistors read fine but since 5 read bad. wondering should i replace all of them?
ok i replaced all power supply fets and the gate resistors.
Figured out and replaced all resistors that wer missing in the output side.
went to power the amp amp and the transformer makes a loud screeching/hissing noise wondering what i can do to fix this problem or what else do i need to check?
Figured out and replaced all resistors that wer missing in the output side.
went to power the amp amp and the transformer makes a loud screeching/hissing noise wondering what i can do to fix this problem or what else do i need to check?
I've never used those FETs but it looks like they should work. I generally use IRF3205s.
It's possible that they failed from any of the following:
* Bad connections between the drivers, gate resistors or FETs
* Defective driver transistors
* Defective FETs (damaged during installation)
* Excessive current draw from the audio section (you didn't say how much current it was drawing).
Before you power it up again, disconnect the red/black twisted wires (from the power supply side of the amp). This will disconnect the power supply from the audio section and you'll be able to test the basic operation of the supply to determine if it has any other problems. Before desoldering them, measure the voltage directly across the wires. If there is more than a few volts, discharge the caps (by shorting across the red/black wires with a large low value resistor - a dummy load works well).
It's possible that they failed from any of the following:
* Bad connections between the drivers, gate resistors or FETs
* Defective driver transistors
* Defective FETs (damaged during installation)
* Excessive current draw from the audio section (you didn't say how much current it was drawing).
Before you power it up again, disconnect the red/black twisted wires (from the power supply side of the amp). This will disconnect the power supply from the audio section and you'll be able to test the basic operation of the supply to determine if it has any other problems. Before desoldering them, measure the voltage directly across the wires. If there is more than a few volts, discharge the caps (by shorting across the red/black wires with a large low value resistor - a dummy load works well).
im gonna replace all fets again this time with the 3205's . before the fets went the amp didnt draw that much current. it was idling fine think the reason they went i didnt have them solderd on the mesha board ver good couple of them were loose. wondering how do i cure the hiss in that transformer.
Did you check the driver transistors (mpsa06/56)?
To confirm that you have a good connection on all of the gates of the PS FETs, measure from one gate leg (near the body of the transistor) to the next FETs gate leg. For all of the transistors in each bank, you should read ~2x the gate resistor value. If you don't, you have an open trace or a bad solder connection. There are 4 banks of PS FETs in this amp.
To confirm that you have a good connection on all of the gates of the PS FETs, measure from one gate leg (near the body of the transistor) to the next FETs gate leg. For all of the transistors in each bank, you should read ~2x the gate resistor value. If you don't, you have an open trace or a bad solder connection. There are 4 banks of PS FETs in this amp.
i checked all 56's and 06's all check fine. Also checked the gate resistors from 1 gate leg to the next i get 20 ohms on all of them . also put meter leads in the positive and negative terminals everything checks fine. when i try to power it up it draws 40 amps of current wondering what shouldi check next
If you don't have any shorted outputs, you need to disconnect the power supply from the audio section. They are connected by the red and black twisted pairs. BEFORE you attempt to desolder them, discharge the caps by shorted between the red/black wires with a resistor or dummy load (with insulated leads). The caps can remain charged for a VERY long time and may have 100+v on them. Desolder them from the power supply end of the wires.
With those 4 wires disconnected, does it draw excessive current?
With those 4 wires disconnected, does it draw excessive current?
If you connect only ground and remote (no B+), do you get a clean square wave on the gates of ALL of the power supply FETs?
If you do, 1 of the transformer's is likely shorted. With a limiting resistor in the B+ line, power the amp up (including B+) and twist, push and pull the transformers to see if the current draw intermittently decreases.
If you do, 1 of the transformer's is likely shorted. With a limiting resistor in the B+ line, power the amp up (including B+) and twist, push and pull the transformers to see if the current draw intermittently decreases.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.