IRF3205s should be a good substitute. If the gate resistors are 100 ohms, replace them with 47 ohm resistors if you use the 3205s. If they're 47 ohms or less, they don't need to be replaced.
If the gate resistors are not going to be replaced, check each one (with the FETs out of the circuit) to make sure each one is within tolerance.
The driver transistors may have also failed.
If you can post a photo of the power supply drive section, it would be helpful if further help is needed. If you can take high resolution photos, zip them and email me a set (only if additional help is needed).
babin_perry@yahoo.com
If the gate resistors are not going to be replaced, check each one (with the FETs out of the circuit) to make sure each one is within tolerance.
The driver transistors may have also failed.
If you can post a photo of the power supply drive section, it would be helpful if further help is needed. If you can take high resolution photos, zip them and email me a set (only if additional help is needed).
babin_perry@yahoo.com
You can measure across each terminal of the driver transistor. If it's shorted you read zero ohms or close to it. A better way would be to remove them from the board and measure each transistor out of the circuit.
I measure each transistor and compare the measurements with the transistors in the other channel. It's usually fairly obvious when one driver transistor is out of whack.
I measure each transistor and compare the measurements with the transistors in the other channel. It's usually fairly obvious when one driver transistor is out of whack.
If you have an oscilloscope, you need to confirm that the drive signal swings cleanly from ground to ~10v.
If you only have a multimeter, you should set it to DC volts and measure the drive signal voltage. It should read ~5-6 volts DC. Do this with the black lead on the chassis ground and the red lead on the gate pads for the FETs (leg 1 of the FETs). Do this for all of the FET gates. If you read approximately the same voltage for all of the gates, the drive circuit is probably OK.
Check the drive circuit after all of the original/blown FETs have been removed.
If you only have a multimeter, you should set it to DC volts and measure the drive signal voltage. It should read ~5-6 volts DC. Do this with the black lead on the chassis ground and the red lead on the gate pads for the FETs (leg 1 of the FETs). Do this for all of the FET gates. If you read approximately the same voltage for all of the gates, the drive circuit is probably OK.
Check the drive circuit after all of the original/blown FETs have been removed.
Are these the transistors that you have in your amp?
http://www.fairchildsemi.com/ds/FQ/FQA85N06.pdf
If so, the 3205s are the wrong part. The specs are close biut the case is the wrong style. I don't remember ever working on an audiobahn with the large case transistors in the power supply.
How many did you order? Where did you buy them from?
Photos help unless the resolution is so bad that it's impossible to make out anything on the board.
http://www.fairchildsemi.com/ds/FQ/FQA85N06.pdf
If so, the 3205s are the wrong part. The specs are close biut the case is the wrong style. I don't remember ever working on an audiobahn with the large case transistors in the power supply.
How many did you order? Where did you buy them from?
Photos help unless the resolution is so bad that it's impossible to make out anything on the board.
i bought 12 of them from here. http://cgi.ebay.com/IRF3205-BY-IR_W...ZWD1VQQ_trksidZp1638.m118.l1247QQcmdZViewItem.i sent you some pics of the amp.if i replace all of them with the irf3205 it won't work?
The 3205 are hefty MOSFETS, they should work anyway even if they are physically smaller. They are 120A each, better than the 85A of the old parts.
In most car amps I've fixed, the TL494 is blown, and it causes the MOSFETS to run hot and blow up when you put new ones in.
Just to be sure, switch out the TL494 IC chip and make sure the negative lead to the IC is good. (I fixed a BOSS amp one time that burned up the MOSFETS, TL494, and the ground trace on the PCB burnt off that was for the TL494)
You can "sample" some TL594 fron Texas Instruments, they are nearly the same as TL494 and pin-to-pin compatible.
In most car amps I've fixed, the TL494 is blown, and it causes the MOSFETS to run hot and blow up when you put new ones in.
Just to be sure, switch out the TL494 IC chip and make sure the negative lead to the IC is good. (I fixed a BOSS amp one time that burned up the MOSFETS, TL494, and the ground trace on the PCB burnt off that was for the TL494)You can "sample" some TL594 fron Texas Instruments, they are nearly the same as TL494 and pin-to-pin compatible.
You should be powering the amp through a relatively small fuse (10-15 amps). This is to protect the transistors in case there is another problem with the amp. You should also have the transistors clamped to the heatsink.
If the amp only pulls current after the remote voltage is applied, you may have:
open transistors in the power supply drive circuit
open gate resistors in the power supply drive circuit
a shorted transformer
shorted rectifiers (rare)
shorted/leaking output transistors (most likely problem)
shorted/leaking driver transistors in the audio circuit
open connections in the bias circuit
If the amp only pulls current after the remote voltage is applied, you may have:
open transistors in the power supply drive circuit
open gate resistors in the power supply drive circuit
a shorted transformer
shorted rectifiers (rare)
shorted/leaking output transistors (most likely problem)
shorted/leaking driver transistors in the audio circuit
open connections in the bias circuit
Are there 14 identical parts (all have the same part number)?
If they don't have the same part number, what are the part numbers (FQA85N06, etc) for each group of parts?
Did you ever take any photos of this amp?
When you say they read nothing, do you mean they read like a direct short or do you mean that the meter reads the same as if you were not touching the leads to anything?
If they don't have the same part number, what are the part numbers (FQA85N06, etc) for each group of parts?
Did you ever take any photos of this amp?
When you say they read nothing, do you mean they read like a direct short or do you mean that the meter reads the same as if you were not touching the leads to anything?
the part numbers are k c5242 0 346 for 7 parts on the right side and fmg325s on two parts on the right side,k a1962 0 332 for 7 on the left ,fmg32r for two also on the left.the 7 one the right side are reading the same and the 7 on the left side are reading the same but the right and left are reading differant.thow do i check the ic chip.i sent you some pics in your email of the power end but they was not very clear.thanks
The 2SC5242 and 2SA1962 are audio output transistors. They are BJTs not FETs.
http://www.toshiba.com/taec/components2/Datasheet_Sync//66/7895.pdf
http://www.toshiba.com/taec/components2/Datasheet_Sync//66/7675.pdf
The FMG parts are rectifiers,The 32S is the positive rectifier. The 32R is the negative rectifier. These will probably read 0 ohms when the meter is connected across the outer legs but should not read 0 ohms from the center leg to the outer legs. If they are reading 0 ohms from the center to the outside, you need to pull them and recheck them off of the board.
What are the numbers on the parts 'in the middle'.
http://www.toshiba.com/taec/components2/Datasheet_Sync//66/7895.pdf
http://www.toshiba.com/taec/components2/Datasheet_Sync//66/7675.pdf
The FMG parts are rectifiers,The 32S is the positive rectifier. The 32R is the negative rectifier. These will probably read 0 ohms when the meter is connected across the outer legs but should not read 0 ohms from the center leg to the outer legs. If they are reading 0 ohms from the center to the outside, you need to pull them and recheck them off of the board.
What are the numbers on the parts 'in the middle'.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.