Mtx 81000d amp Crunchy insides - diyAudio
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Old 29th May 2008, 07:33 AM   #1
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Default Mtx 81000d amp Crunchy insides

I have had this amp for a couple years now and it has worked great. Unfortunately it gave up. It was draining the battery in my car. So off comes the cover and i find 4 of the fet's burned/cracked and 1 resistor. Its a surface mount and of course the #'s are gone.
Is there somewhere i can find the value for that resistor # 436? And what do you guys make of this draining the battery? It sounds to me like that are bigger problems but nothing else appears to be wrong.
Thanks for your help
Brian
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Old 29th May 2008, 08:22 AM   #2
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R435 and R436 are the same, 39.2 ohms. You would need to replace all 8 of the power supply FETs.

You need to check the output transistors before you do anything else. If they're shorted, the amp may be difficult to repair.

If they're OK, the PZTA56s near the small toroidal transformer may be defective. If they are, the 10 ohm resistors connected between legs 1 and 3 may be open.
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Old 29th May 2008, 03:38 PM   #3
jol50 is offline jol50  United States
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12v often goes to the PS fets direct so if they are burned current may leak when amp is off.
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Old 1st June 2008, 08:31 AM   #4
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Quote:
Originally posted by Perry Babin
R435 and R436 are the same, 39.2 ohms. You would need to replace all 8 of the power supply FETs.

You need to check the output transistors before you do anything else. If they're shorted, the amp may be difficult to repair.

If they're OK, the PZTA56s near the small toroidal transformer may be defective. If they are, the 10 ohm resistors connected between legs 1 and 3 may be open.
I was thinking i should just change them all. Now im sure to do that. I have checked the PZTA56s and the outputs. all check out good so far.
I think this should be pretty straight forward. Fingers crossed.
Where do you recommend to order good quality parts?
Thanks, for your help on this. It's nice to find stand up people such as yourself.

Quote:
Originally posted by jol50
12v often goes to the PS fets direct so if they are burned current may leak when amp is off.
Im definitely thinking that would be the source of my dead battery situiation. Thanks for the help.
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Old 1st June 2008, 11:18 AM   #5
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Mouser and DigiKey are both reliable suppliers. Mouser has no minimum order so if you need less than $25 of parts, that would be a better choice.
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Old 2nd June 2008, 10:50 PM   #6
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Mouser was recommended to me by a friend also. I think that's where ill go.
Again thanks for the help.
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Old 3rd June 2008, 02:45 AM   #7
jol50 is offline jol50  United States
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I've been getting things from Mouser w/no problems. I seem to get things faster using USPS for some reason. I just screwed up on a couple things and got smd I did not want, so if you are not used to ordering be careful of parts that come both ways like op amps and transistors.
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Old 4th June 2008, 03:19 AM   #8
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Quote:
Originally posted by jol50
I've been getting things from Mouser w/no problems. I seem to get things faster using USPS for some reason. I just screwed up on a couple things and got smd I did not want, so if you are not used to ordering be careful of parts that come both ways like op amps and transistors.
Thanks for the head's up
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