I'm replacing all 8 FET's in the power supply section of an A600. I'm pretty new to this but came across some threads about upgrading them to stronger parts. IRFZ48V's seem to be the strongest parts I could find so that's what I ordered. Additional reading revealed information about different gate resistor values for different FET's.
Can anyone tell me what values to use for the gate resistors when using IRFZ48V transistors?
Can anyone tell me what values to use for the gate resistors when using IRFZ48V transistors?
I just measured the existing ones and they are 47's, so I'll leave 'em. I bought the amp "non-working" and found 3 z44n's that looked about like they'd exploded since there were parts of the actual silicon missing revealing whatever the core is made of. All the caps, the board, and all else looks great. I'm crossing my fingers this will come alive once I get the z48v's in.
The outside of the transistor is some sort of epoxy/resin/plastic. The parts inside that look like broken glass is the silicon that makes up the transistor. The tiny rectangle in the center of the metal tab in the following image is the transistor (not intact due to the case being forced open).
http://www.bcae1.com/repairbasicsforbcae1/images/transistordies/IMG_5518_IR_IRFZ44Nb.jpg
This one shows what a silicon die looks like when intact. This is only one example. The various manufacturers use different designs, generally trying to minimize the amount of silicon to meet the specifications of a device.
http://www.bcae1.com/repairbasicsforbcae1/images/transistordies/IMG_5494_Hitachi_2SK135b.jpg
http://www.bcae1.com/repairbasicsforbcae1/images/transistordies/IMG_5518_IR_IRFZ44Nb.jpg
This one shows what a silicon die looks like when intact. This is only one example. The various manufacturers use different designs, generally trying to minimize the amount of silicon to meet the specifications of a device.
http://www.bcae1.com/repairbasicsforbcae1/images/transistordies/IMG_5494_Hitachi_2SK135b.jpg
Well, I soldered in the z48's and went to test it. It popped the 50 amp fuse in my 8ga cable as soon as I plugged in just the power connector. I took the cover off to check for damage and the FET's all visually look fine but 7 of the 8 are showing shorts between all 3 legs and also between the legs and the metal tab on the bottom.
I didn't measure them before installing but wish I would have. Is there anything else I should be taking a look at before trying another batch of FETs?
I didn't measure them before installing but wish I would have. Is there anything else I should be taking a look at before trying another batch of FETs?
Still working on this one. I'm curious about the 2 legged rectifier diodes. There are two of them on each side. On one side they read a very high resistance value and on the other side - very low as in .3~.4 ohms. Is this an indication that they are bad? Or is there something else in a parallel fashion to them that is making it seem so? There is no visual damage to them, but I guess they could be damaged internally.
Pardon me, but what kind of power supply fets were originally in this amp? IRFZ44/46?
It wont make a substantial different, but since this is your amp and you are wanting to upgrade you might want to look at IRF3205 as they are stonger still than the IRFZ48. I'm not sure if the drive circuit will need modification though; or if the upgrade will actually make anything better.
It wont make a substantial different, but since this is your amp and you are wanting to upgrade you might want to look at IRF3205 as they are stonger still than the IRFZ48. I'm not sure if the drive circuit will need modification though; or if the upgrade will actually make anything better.
I finally got a chance to remove all 4 of the two legged rectifiers. Only one of them appears to be shorted but on the board it was appearing that both of them on that side were shorted. I'm guessing they must be paralell pairs. I replaced all 4 of them anyway with brand new parts. I haven't tried re-powering it yet, but I do have a pack of 10 amp atc fuses ready to test with.
I've measured the output transistors and haven't seen anything shorted out and visually everything else on the board looks good. I did measure Q17 and Q25 which are small barrel shaped transistors near the center of the board on the power supply end and found a couple of legs on each to read .2 ohms. Can anyone tell me the function of these two small transistors or have a schematic to tell how they tie in?
I've measured the output transistors and haven't seen anything shorted out and visually everything else on the board looks good. I did measure Q17 and Q25 which are small barrel shaped transistors near the center of the board on the power supply end and found a couple of legs on each to read .2 ohms. Can anyone tell me the function of these two small transistors or have a schematic to tell how they tie in?
I'm just an amateur working on a first amp repair so I don't ultimately know what an emitter resistor is, but I know that one of the terminals on a transistor is called the emitter, so I went to the closest ones on the heatsink and found a small tan 1 ohm resistor electrically connected to a leg. From the other side of that 1 ohm resistor I was then able to get direct continuity to the small barrel shaped transistors. I actually think I spoke incorrectly of the component numbers - they are Q12 and Q30. Again, two legs on each of these are showing direct path to what I assume are the emitter resistors.
This picture shows the transistors in question and the corresponding flat heatsink transistors. One thing I found odd was that it is a BDT81 on one side and a BDT82 on the other. The 4 transistors immediately next to each are all BDT82's.
I'm guessing that the MPS A06 & MPS A56 transistors are defective?
This picture shows the transistors in question and the corresponding flat heatsink transistors. One thing I found odd was that it is a BDT81 on one side and a BDT82 on the other. The 4 transistors immediately next to each are all BDT82's.
An externally hosted image should be here but it was not working when we last tested it.
I'm guessing that the MPS A06 & MPS A56 transistors are defective?
Have you read the basic amp repair page?
The transistors that you're referring to are used as part of a protection circuit for the voltage regulators. The large transistors circled are used as regulators.
Emitter resistors connect to the emitter leg of the output transistors. 0.68 ohm in this amp.
There's generally a 100 ohm resistor between 5 and 7. It's used to set the deadtime for the IC. On the Rev.S, I think there may have been a 10 ohm resistor.
The transistors that you're referring to are used as part of a protection circuit for the voltage regulators. The large transistors circled are used as regulators.
Emitter resistors connect to the emitter leg of the output transistors. 0.68 ohm in this amp.
There's generally a 100 ohm resistor between 5 and 7. It's used to set the deadtime for the IC. On the Rev.S, I think there may have been a 10 ohm resistor.
I read through the basic amp repair page and am trying to learn as I go. I have a background in mechanical engineering, but some of this electrical stuff is pretty unfamiliar to me.
Based on what you said, then I believe the emitter resistors are the large grey ones toward the RCA end of the board in front of 8 transistors per side and they all check out fine.
Based on what you said, then I believe the emitter resistors are the large grey ones toward the RCA end of the board in front of 8 transistors per side and they all check out fine.
Cheap sockets are a problem. If you use a socket, get the type that either has milled pins or the ones that have contacts on both sides of each of the individual sockets.
I've never heard of anyone damaging a DIP IC by using too much heat. The board would be charcoal by the time the IC got hot enough to suffer damage.
I've never heard of anyone damaging a DIP IC by using too much heat. The board would be charcoal by the time the IC got hot enough to suffer damage.
I just wanted to update this to let everyone know I solved the problem and to thank everyone for their guidance.
It turned out to be the 16 pin IC. After I replaced that, using a good machined socket, it powered up and didn't blow the 10 amp fuse. I then connected an old bookshelf speaker and music sounded normal and clean. Once I get my crossover set up I will test it on my 10w3 and see how it does on bass duty.
It turned out to be the 16 pin IC. After I replaced that, using a good machined socket, it powered up and didn't blow the 10 amp fuse. I then connected an old bookshelf speaker and music sounded normal and clean. Once I get my crossover set up I will test it on my 10w3 and see how it does on bass duty.
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