i think i may have ran into another problem. ive just replaced the fets i replaced before and when i test each one they show some resistance, but when the board is screwed back into the amp with the clamps on the fets they all show 0ohms for some reason :s
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Did you power it up between the time you replaced them and the time when you found that they read shorted from 2-3?
Are all of the insulators in place and intact (measure from the resistance from the center leg to the clamp)?
Are all of the insulators in place and intact (measure from the resistance from the center leg to the clamp)?
no it hasnt been powered up since ive replaced them. are the insulators the thin piece of plastic type material in the shape of each fet? they are still there but not sure if they are on each fet as they did move around when i took the board out and put it back in.... they go under the fet when resting on the heatsink bar and then the clamp goes on top... are they the ones? not every fet has got one :S
Yes. The clear pieces are mica insulators. Every FET and rectifier that mounts to the heatsink must have one.
oops my bad.... two of them got stuck to each other because of the grease... sorry about that.. im just about to adjust the potetionmeters now... wish me gud luck!!!
oh i feel like burning this thing!!! just hooked it up... the bias posts were turned fully conuterclockwise as you said....it powered up but the protection light and power light were flashing....put black probe onto non bridging speaker terminal and red on center leg off Q504 to adjust VR601 with the meter on the 50dcv setting but the meter did not move :s and then few seconds later the fets blew....AGAIN!!!! 🙁 🙁... should i bin it? or is there some other problem solving that i could have missed?
Which FETs failed?
Did you have a 15 amp fuse in the B+ line?
Were the FETs clamped tightly to the heatsink?
Did you have a 15 amp fuse in the B+ line?
Were the FETs clamped tightly to the heatsink?
i seen a lil smoke come from the ones i changed in the first place. yea i had a 15amp fuse in the B+ line, when i first turned the amp on it ran for abt 3 secs and blew the fuse so i put another 15amp fuse and thats when it ran for abit but then blew the FETs. Im pretty sure the FETs were clamped tightly to heatsink. The FETs are still on the board i havent unsoldered them yet because it put me off 🙁
If the fuse blew, you should have stopped there and let us know.
While the power supply FETs are out of the board (no power applied), measure the resistance from the gate pad of each FET to the chassis ground terminal. They should all read ~110 ohms. Is that what you have?
Double-check this AFTER reinstalling the FETs but before applying power. Touch the meter probe to the gate leg of the FET instead of the gate pad. Do you again read ~110 ohms from the gate leg of every power supply FET to chassis ground?
Apply power (including remote) and measure the DC voltage on all of the gate pads for the FETs that have been failing. Compare that voltage to voltage on the gate pads for the side that has not failed. They should be nearly identical. Is that what you have?
After replacing the power supply FETs again, make absolutely sure that they're clamped tightly to the sink (or at least clamped tightly to the riser plate) and make absolutely sure that none read anything near 0 ohms from their center leg to the clamp that's holding them down.
This time, disconnect the 6 conductor cable that connects the power supply board to the amp board. Power up the amp. How much current does it draw from the 12v power supply?
While the power supply FETs are out of the board (no power applied), measure the resistance from the gate pad of each FET to the chassis ground terminal. They should all read ~110 ohms. Is that what you have?
Double-check this AFTER reinstalling the FETs but before applying power. Touch the meter probe to the gate leg of the FET instead of the gate pad. Do you again read ~110 ohms from the gate leg of every power supply FET to chassis ground?
Apply power (including remote) and measure the DC voltage on all of the gate pads for the FETs that have been failing. Compare that voltage to voltage on the gate pads for the side that has not failed. They should be nearly identical. Is that what you have?
After replacing the power supply FETs again, make absolutely sure that they're clamped tightly to the sink (or at least clamped tightly to the riser plate) and make absolutely sure that none read anything near 0 ohms from their center leg to the clamp that's holding them down.
This time, disconnect the 6 conductor cable that connects the power supply board to the amp board. Power up the amp. How much current does it draw from the 12v power supply?
im sorry about that..i just thought it may be a little glich and tried again with another fuse.
are the gate pads the plates with the holes on the FETs on the back? just to make it clear... check each FET when its desoldered out of the board with the chassic ground terminal to see if it reads ~110 ohms. Then resolder new ones? back into the board and check again but from the gate leg.
then check dc voltage from the gate pads to chassis ground terminal on failed side and compare to the good side. is that correct? sorry i just want to make sure before anything else happens.
when i did check the FETs before powering up the amp after the insulator incidence... they all showed resistance but it started from 0ohms and started working up the scale slowly on all FETs... does that sound right? the meter was on the lowest resistance setting.
to check the current draw am i ok to put the meter probes on the ground and positive terminal on the amp while it is switched on? or keep the headunit turned off but the wires all connected to the amp?
thanks for bearing with me.... appreciate it.
are the gate pads the plates with the holes on the FETs on the back? just to make it clear... check each FET when its desoldered out of the board with the chassic ground terminal to see if it reads ~110 ohms. Then resolder new ones? back into the board and check again but from the gate leg.
then check dc voltage from the gate pads to chassis ground terminal on failed side and compare to the good side. is that correct? sorry i just want to make sure before anything else happens.
when i did check the FETs before powering up the amp after the insulator incidence... they all showed resistance but it started from 0ohms and started working up the scale slowly on all FETs... does that sound right? the meter was on the lowest resistance setting.
to check the current draw am i ok to put the meter probes on the ground and positive terminal on the amp while it is switched on? or keep the headunit turned off but the wires all connected to the amp?
thanks for bearing with me.... appreciate it.
The gate pad is the solder pad on the board to which the gate leg is soldered.
You need to check the gate pad to chassis ground and after the FETs are reinstalled, check from the gate leg of the FET to chassis ground.
The resistance does sometimes change. It's generally due to a capacitor being either directly or indirectly across the circuit you're testing.
You probably can't check the current draw with your meter. You DEFINITELY don't want to set it up for measuring amperage and then touch the probes across the B+ and ground. It's likely to damage your meter. Does your power supply have an amp meter?
You need to check the gate pad to chassis ground and after the FETs are reinstalled, check from the gate leg of the FET to chassis ground.
The resistance does sometimes change. It's generally due to a capacitor being either directly or indirectly across the circuit you're testing.
You probably can't check the current draw with your meter. You DEFINITELY don't want to set it up for measuring amperage and then touch the probes across the B+ and ground. It's likely to damage your meter. Does your power supply have an amp meter?
ive got dcv settings on my meter.... heres some pics of it for you:
what kind of amp meter would a power supply have? ive got a volt meter lying around for car installation.... could that be any use? it only shows up to 16v though.
what kind of amp meter would a power supply have? ive got a volt meter lying around for car installation.... could that be any use? it only shows up to 16v though.
quick update.... just took out the blown FETs.... only two were shot but ill replace them all. I checked from the gate pad to chassis ground terminal and yes it did show 110ohms.
Im going to install the new FETs tomorrow and check from gate leg to ground terminal and will update you. thanks
Im going to install the new FETs tomorrow and check from gate leg to ground terminal and will update you. thanks
What make/model power supply are you using to power the amp?
Were you asking about DC amps when you posted the photos of the meter?
Were you asking about DC amps when you posted the photos of the meter?
erm im just plugging it into the wiring i have got in the car to power the amp... dont have an actual power supply... its 8 gauge wiring and i use 15amp blade fuse when i have been powering it up. i posted pics of the meter because you said i may not be able to check how much power the amp is using from the 12v supply so just wanted to show you what im working with and see what setting i should keep it on when checking the power.
That meter is only capable of passing 250ma (0.25 amps) so it can't be used in current mode to determine the current draw of the amplifier.
To measure the current draw with that meter, you'd have to have a current shunt resistor (low value, high wattage resistor) and you'd measure the DC voltage across it.
To measure the current draw with that meter, you'd have to have a current shunt resistor (low value, high wattage resistor) and you'd measure the DC voltage across it.
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