You need to be careful when you use the terms 'always' or 'exactly'. Virtually nothing is absolute.
Power supply FETs and class A, AB and B outputs are sometimes easy to sub but class D amps are a different animal. In some class D amps, the deadtime is determined by the gate load. Changing the FET changes the load and the amp may have too little deadtime. This can result in the amp failing. It may not fail immediately. A change in the operating temperature may be enough to make the amp fail if the deadtime isn't right. Too much deadtime can also cause problems.
At least a couple of times a month I have to deal with this problem. People either send me an amp or email me about amps and the only problem is that they (or a previous tech) used a substitute part. This is the reason I am so concerned when substitute parts are mentioned with class D amps.
As an example, the early MTX amps like the 81000d used the SSP45N20A. That transistor was discontinued and the new SSP45N20B was the replacement (same manufacturer, VERY close specs). The B version would NOT work as a sub.
In a different amp (one of the many clones that has the fan between the driver board and the two inductors), the IRFB42N20D may seem like an upgrade over the original IRFB31N20D. In some amps, they will work and never have a problem. In other amps, they work for a while but the amp will be unreliable (slight changes in operating conditions will cause the FETs to fail). In other amps, they will not even power up (they go directly into protect. Replacing them with the original parts makes the amps as reliable as they were originally.
In this instance, if the IRF3415 amp uses the same EXACT driver components, the 260N may be an upgrade. That's not always the case when using substitute parts.
The braid 'may' be OK but you won't know until you buy it. Many times, braid sits around, exposed to air and it oxidizes. That makes it very nearly useless. Adding liquid flux to poor quality braid can make it usable. The braid I generally buy is ~$50/100ft. I dread having to buy a new roll but it works and saves time in the long run. The roll will last more than a year for me. I generally only use it to clean up SMD pads. Most of the desoldering I do is with a desoldering pump (DS017 Edsyn).
Power supply FETs and class A, AB and B outputs are sometimes easy to sub but class D amps are a different animal. In some class D amps, the deadtime is determined by the gate load. Changing the FET changes the load and the amp may have too little deadtime. This can result in the amp failing. It may not fail immediately. A change in the operating temperature may be enough to make the amp fail if the deadtime isn't right. Too much deadtime can also cause problems.
At least a couple of times a month I have to deal with this problem. People either send me an amp or email me about amps and the only problem is that they (or a previous tech) used a substitute part. This is the reason I am so concerned when substitute parts are mentioned with class D amps.
As an example, the early MTX amps like the 81000d used the SSP45N20A. That transistor was discontinued and the new SSP45N20B was the replacement (same manufacturer, VERY close specs). The B version would NOT work as a sub.
In a different amp (one of the many clones that has the fan between the driver board and the two inductors), the IRFB42N20D may seem like an upgrade over the original IRFB31N20D. In some amps, they will work and never have a problem. In other amps, they work for a while but the amp will be unreliable (slight changes in operating conditions will cause the FETs to fail). In other amps, they will not even power up (they go directly into protect. Replacing them with the original parts makes the amps as reliable as they were originally.
In this instance, if the IRF3415 amp uses the same EXACT driver components, the 260N may be an upgrade. That's not always the case when using substitute parts.
The braid 'may' be OK but you won't know until you buy it. Many times, braid sits around, exposed to air and it oxidizes. That makes it very nearly useless. Adding liquid flux to poor quality braid can make it usable. The braid I generally buy is ~$50/100ft. I dread having to buy a new roll but it works and saves time in the long run. The roll will last more than a year for me. I generally only use it to clean up SMD pads. Most of the desoldering I do is with a desoldering pump (DS017 Edsyn).
Thanks for explanation Perry,I will keep it in mind.
To rocco4796
Don't even try to power up the amp before you changed drivers transistors and gates resistors.In my T20001BD almost all of them were dead.And also you have to know ,the ground ,I mean negative terminal in this amp going through the body of the amp.All drains of power suplly fets connected together through the case of the amp.Before power it up ,you have to install board inside the case ,and screw it to the body
To rocco4796
Don't even try to power up the amp before you changed drivers transistors and gates resistors.In my T20001BD almost all of them were dead.And also you have to know ,the ground ,I mean negative terminal in this amp going through the body of the amp.All drains of power suplly fets connected together through the case of the amp.Before power it up ,you have to install board inside the case ,and screw it to the body
All checked. 9 out of 24 gate resistors of 10 ohm (12 each amp) are failed. I think I'll change all 24. Then, I have in the same area also 4 100ohm resistors and 4 1kohm resistors each amp, with a total of 16. 8 of them are failed. I didn't check the mmbta56 and 06, I think it's useless...Nice damage, isn't it?
You'll need a small torch (similar to the following).
http://www.radioshack.com/product/index.jsp?productId=2062753
or
http://www.bernzomatic.com/PRODUCTS...etail/mid/1147/xmid/6966/xmfid/3/Default.aspx
You'll have to...
*clean the compound from the insulators
*clamp one (adjacent) FET to the insulator (binder clip or large forceps - clamp should be lightweight)
*heat the insulator behind the unclamped FET until it releases
*desolder the legs of the FET and remove it
*tin the back of the new FET
*check the FET to confirm that there is absolutely no continuity between leg 1 of the FET and the other legs. sometimes they fail if you heat them too much when tinning them
*place the new FET in place and solder the center leg
*heat the back of the insulator while applying light pressure to the FET
*when the solder melts and the FET drops onto the insulator, hold it on the insulator and remove the heat
*solder all of the legs on the newly replaced FET
*then do the next FET on the insulator
I prefer to do it this way because the insulator remains at the correct height and everything remains aligned so there are no problems when you go to reassemble it.
Be careful not to use too much heat or dislodge any of the other small components on the boards.
If possible, clamp the 3 terminal jumper to the insulator. If you use too much heat, they can become desoldered.
http://www.radioshack.com/product/index.jsp?productId=2062753
or
http://www.bernzomatic.com/PRODUCTS...etail/mid/1147/xmid/6966/xmfid/3/Default.aspx
You'll have to...
*clean the compound from the insulators
*clamp one (adjacent) FET to the insulator (binder clip or large forceps - clamp should be lightweight)
*heat the insulator behind the unclamped FET until it releases
*desolder the legs of the FET and remove it
*tin the back of the new FET
*check the FET to confirm that there is absolutely no continuity between leg 1 of the FET and the other legs. sometimes they fail if you heat them too much when tinning them
*place the new FET in place and solder the center leg
*heat the back of the insulator while applying light pressure to the FET
*when the solder melts and the FET drops onto the insulator, hold it on the insulator and remove the heat
*solder all of the legs on the newly replaced FET
*then do the next FET on the insulator
I prefer to do it this way because the insulator remains at the correct height and everything remains aligned so there are no problems when you go to reassemble it.
Be careful not to use too much heat or dislodge any of the other small components on the boards.
If possible, clamp the 3 terminal jumper to the insulator. If you use too much heat, they can become desoldered.
Not really. It's a bit time consuming to do the first time but it gets easier.
Is there a reason you don't want to use a torch?
If you decide to clamp them to the heatsink, you'll likely have to sand the heatsink smooth. Most are too rough to promote good heat transfer without the heat spreader/insulator.
Is there a reason you don't want to use a torch?
If you decide to clamp them to the heatsink, you'll likely have to sand the heatsink smooth. Most are too rough to promote good heat transfer without the heat spreader/insulator.
I have limited experience with these amps but I would suggest checking everything between the driver transformer and the FETs. If there is a question as to it being defective, replace it. There's no point in taking a chance on blowing the outputs when you apply power.
When you apply power, you may want to insert 2-4 ohm current limiting resistors or fuses (~5 amps) in the red and blue jumper wires to help prevent blowing the new FETs if there is another fault.
You can cause the insulator to delaminate if you use a large torch but with a small torch, there is little chance of doing any damage. You'll remove the heat as soon as the transistor is released from the insulator. Apply gentle force when heating the insulator so you'll know precisely when the solder becomes molten.
When you apply power, you may want to insert 2-4 ohm current limiting resistors or fuses (~5 amps) in the red and blue jumper wires to help prevent blowing the new FETs if there is another fault.
You can cause the insulator to delaminate if you use a large torch but with a small torch, there is little chance of doing any damage. You'll remove the heat as soon as the transistor is released from the insulator. Apply gentle force when heating the insulator so you'll know precisely when the solder becomes molten.
I am so glad I found this forum. I was just actually reading on Perry Babin's site. I have 3 t30001bd in my expedition. I had a loose ground wire on one of them and it blew the power supply and sparks and smoke came out of it. lol
I am trying to fix it myself and I need some help and a schematic. I am willing to pay for some assistance. I can solder very good and can replace components but thats about it. I cut the legs off the transistors on the mesha board and very quickly heated on my electric range(stove) heats the solder very quickly and evenly, and they came right off. So far I have ordered and received
14 HUF75344G3 EXTRA IF ONE GETS DAMAGED INSTALLING
12 MMBD914
12 BZX84C33
12 MMBTA06
12 MMBTA56
Thanks for the help.
I am trying to fix it myself and I need some help and a schematic. I am willing to pay for some assistance. I can solder very good and can replace components but thats about it. I cut the legs off the transistors on the mesha board and very quickly heated on my electric range(stove) heats the solder very quickly and evenly, and they came right off. So far I have ordered and received
14 HUF75344G3 EXTRA IF ONE GETS DAMAGED INSTALLING
12 MMBD914
12 BZX84C33
12 MMBTA06
12 MMBTA56
Thanks for the help.
You need to check all of the gate resistors for the power supply FET.
You also need to check the drive signal. With your multimeter set to DC volts and the black probe on the chassis ground terminal, measure the voltage on pins 13 and 16 of the SG3526. You should have approximately that same voltage on the gate pads for the power supply FETs.
Did any of the output transistors fail?
email me if you want the power supply schematic.
babin_perry@yahoo.com
You also need to check the drive signal. With your multimeter set to DC volts and the black probe on the chassis ground terminal, measure the voltage on pins 13 and 16 of the SG3526. You should have approximately that same voltage on the gate pads for the power supply FETs.
Did any of the output transistors fail?
email me if you want the power supply schematic.
babin_perry@yahoo.com
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.