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Old 1st October 2011, 08:37 PM   #1
chipper is offline chipper  United States
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Default Power 551S blown driver transistor

Hi all, I just got myself a nice project amp for next to nothing. Anyway when I received it the power supply fets were blown up (IRF3205's were all destroyed) and including one of the small surface mount transistors had a fry mark in the center or it. The legs were cut on all the outputs in the left channel (obviously why it fried it's self) the right channel transistors are still good. Anyway what are some good replacement transistors for the driver circuit? I already ordered 20 irf3205 mosfets I know I don't need 20 but they'll come in handy for later amp repairs. How much would the drivers cost?? Thanks! Also how would the idea be if I snagged a mehsa strip from a punch 200a4? I put the circuit board side by side transistor to transistor. They seem to math up perfectly because someone ripped one of the power supply fets off the mehsa strip. Any thoughts, comments, help appreciated. Thanks
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Old 1st October 2011, 08:40 PM   #2
chipper is offline chipper  United States
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Also the 200a4 is a broken amp so basically a doner amp ha
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Old 1st October 2011, 09:26 PM   #3
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The PNP driver transistors typically fail in the power supply. I generally use MMBTA56s. When ordering the drivers, order at least 10 each of the MMBTA56 and MMBTA06.

If the MEHSA module matches the one in the other amp, there's no reason that you can't use the audio section of it. If the damaged power supply pad is connected with the audio section, you'll have to cut it free and use the one that's in your amp now.

If/when you cut it, do so through the center of one of the mounting holes.
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Old 2nd October 2011, 02:30 AM   #4
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htere is also a guy on here that has all the old original mesha parts for doing warrenty repair on these amps. what's wrong with the 200a4?
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Old 2nd October 2011, 03:13 PM   #5
chipper is offline chipper  United States
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I used the whole strip and all the mounting pads are all the same and matching. Soldering the transistors back on wasn't easy but they're all back on and looks good. I already bought those parts now just waiting for the irf3205's & the drivers now.

Also has the TL494C chip ever gone bad on these type of amps when the driver transistors fail? When I checked for any gate voltage I got 9 vDC on one side and the 12 vDC on the other side.
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Old 2nd October 2011, 03:15 PM   #6
chipper is offline chipper  United States
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Quote:
Originally Posted by AKHeathen View Post
htere is also a guy on here that has all the old original mesha parts for doing warrenty repair on these amps. what's wrong with the 200a4?
It has a distorted LL channel that I couldn't figure out what was wrong.
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Old 2nd October 2011, 07:58 PM   #7
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The 494 rarely ever fails in these amps. The driver transistors act as a buffer and protect the IC.
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Old 3rd October 2011, 07:52 PM   #8
chipper is offline chipper  United States
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Quote:
Originally Posted by Perry Babin View Post
The 494 rarely ever fails in these amps. The driver transistors act as a buffer and protect the IC.


Do you have a diagram on how the driver transistors are set up? I took off the originals and now I don't know the polarity for them. I'd like to see a pic of the drivers if you can mark the polarity of the transistors.

& can you do the same for a punch 201S this one has the same problem. Thanks!
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Old 3rd October 2011, 07:54 PM   #9
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What is the exact part number or marking of the transistors you're installing?
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Old 3rd October 2011, 08:18 PM   #10
chipper is offline chipper  United States
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MMBTA56LT1 & MMBTA06LT1
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