Hi guys, new to the forum and looking for some help with a MTX Thunder 81001. The output filter caps were blown and one of the output fets is bad. The other ones seem good in circuit but I`ll pull them to double check.
Can i replace one of the fets or do i have to replace them all to get them to match? Also 4 resistors got hot if someone could confirm the value of r490-494.
Do these work of a split +- rail voltage or a single supply. This is the first class D I`ve seen.
Any idea what causes a failure like this?
Can i replace one of the fets or do i have to replace them all to get them to match? Also 4 resistors got hot if someone could confirm the value of r490-494.
Do these work of a split +- rail voltage or a single supply. This is the first class D I`ve seen.
Any idea what causes a failure like this?
http://www.diyaudio.com/forums/car-...-identify-4-burned-resistors.html#post2308980
Any FETs that are in parallel with the failed FET need to be replaced. The replacement parts should be from the same batch of parts (same date code).
The amp has positive and negative rails.
Any FETs that are in parallel with the failed FET need to be replaced. The replacement parts should be from the same batch of parts (same date code).
The amp has positive and negative rails.
Thanks for the response. Can i just order 6 of the IRFP240's from Digikey and expect to get the same date code? If not a source would be great🙂. Anything special about the caps in these?
FYI, You can also email MTX for the values of Resistors and Caps, etc. They will not give you a copy of the schematics, but as long as you know the number on the board, they will give you the proper info.
Ask the salesperson if you can get all with the same date code. If they can't guarantee it, or them in multiples of 10 (order extras) and you are more likely to get transistors from the same batch.
Installed my parts today, 6 fets (same date code) 4 10k resistors and the 8 output filter caps. The amp is running and the short lite is out🙂.
How hot should this be running with no input. I have an 8 ohm speaker connected but no input signal and after about 40min the fans are on and its very hot. Measured input current 4.6A at idle. Also got 180khz 1vpp on the output. Is this normal or do I have other faults?
How hot should this be running with no input. I have an 8 ohm speaker connected but no input signal and after about 40min the fans are on and its very hot. Measured input current 4.6A at idle. Also got 180khz 1vpp on the output. Is this normal or do I have other faults?
Let it cool down completely. Power it up and monitor the temperature of the heatsink. Does one particular area (behind the outputs, behind the power supply FETs...) tend to neat up more quickly?
What's the DC voltage measured directly across the positive and negative speaker terminals?
What's the DC voltage measured directly across the positive and negative speaker terminals?
When I first power it up there is some varying dc on the output but it settles down after about 10 secs and ends up at 30mv dc. The heat is coming from the bank of 4 to220's behind the rca inputs. I pulled the bar off them and the IRF540 seems to be generating the most heat when i touched it directly.
Thanks for the help with this btw.
Thanks for the help with this btw.
The inductors operate at relatively high temperatures. Even at idle, they'll get too hot to hold your hand on continuously.
The two regulators will get hot very quickly. Do not operate the amp without having them clamped. If they fail, they can cause extensive damage. They can fail within seconds if not clamped tightly to the heatsink.
When the fans were running, were they running at full speed? You can determine if they were at full speed by measuring the voltage at the white 2-pin connector for each one. If they were not running at full speed, it's likely that the temperature wasn't a problem.
The two regulators will get hot very quickly. Do not operate the amp without having them clamped. If they fail, they can cause extensive damage. They can fail within seconds if not clamped tightly to the heatsink.
When the fans were running, were they running at full speed? You can determine if they were at full speed by measuring the voltage at the white 2-pin connector for each one. If they were not running at full speed, it's likely that the temperature wasn't a problem.
With the cover off it took 40min for one fan to start. Waited another 40 and both fans were spinning with 2 vcd on the plugs. This is with a 4 ohm speaker and no input signal.
Its drawing 4.5A and cant hold my hand on the heatsink for long.
Its drawing 4.5A and cant hold my hand on the heatsink for long.
I never removed the heatsink but i did have the bars off both sides on the output end. I did notice the board flex about 1/4" away from the heatsink a few times when handling it. Is there a thermal sensor under there?
Yes. There's a soft thermal interface pad that needs to be placed between the thermistor and the heatsink. It's possible that it fell out of place when the heatsink was separated from the board. I think it's on the corner of the heatsink that's nearest the HCPL3120 opto-couplers. There are likely two diagonal traces that exit from that corner. I think that's where the thermistor is.
The attached photo shows the thermistor and the thermal pad (moved off of the thermistor so the thermistor would be visible). This is on a 7801 which should be similar to the amp you have.
The attached photo shows the thermistor and the thermal pad (moved off of the thermistor so the thermistor would be visible). This is on a 7801 which should be similar to the amp you have.
Attachments
Checked the thermal interface and it was okay but i moved it slightly to give it a new place to contact the sensor. Reassembled and it looks the same as before.
Any other sugestions, maybe i'll run it with a load and some input for a while and see what happens.
Any other sugestions, maybe i'll run it with a load and some input for a while and see what happens.
With the cover on ran this for 3 hours 54vpp into a 4 ohm resistor @100hz. The chrome ends got hot but could hold them np, rest of the amp was warm at most. Maybe its okay?
It's probably OK.
A better indicator may be the rate at which the heatsink behind the various groups of transistors heats up. If you drive the amp hard and no section of the heatsink heats up quickly, it's probably OK. If one section (behind the outputs, behind the power supply FETs...) heats up very quickly when driven hard, that could indicate that there's a problem.
A better indicator may be the rate at which the heatsink behind the various groups of transistors heats up. If you drive the amp hard and no section of the heatsink heats up quickly, it's probably OK. If one section (behind the outputs, behind the power supply FETs...) heats up very quickly when driven hard, that could indicate that there's a problem.
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