In the process of repairing a US Amps Merlin MD1D that blew an output, which was replaced by the owner, and then blew up the power supply.
I will be replacing the PS FETS, the outputs and the HIP4080 IC but there is a resistor close to the output terminals that is completely obliterated. The board designation is R50P. Can someone please help me out by identifying what goes in this location. I have added pics for assistance. Thanks.
I will be replacing the PS FETS, the outputs and the HIP4080 IC but there is a resistor close to the output terminals that is completely obliterated. The board designation is R50P. Can someone please help me out by identifying what goes in this location. I have added pics for assistance. Thanks.
Attachments
The owner of this amp is hoping for an economical fix. I have it put back together with reused parts and it is playing, but when the volume is turned up, it cuts off and restarts just like if it had a loose ground and wasn't getting enough current. The protection light never comes on, the amp just shuts off, and then powers back up. I am hoping to track down the exact cause without just replacing everything. He should be replacing 12 PS FETS, 8 outputs, and 1 output IC but we are hoping to find the exact cause of its current shutdown issue without doing a complete rebuild.
POWER SUPPLY FETS?
Six of the PS FETS were blown. 2 sets of three, each set from one side of each transformer. I took the good originals from one transformer and put them to complement the other originals on the other transformer. I then installed six recycled 70N06 FETS to the two banks of the remaining transformer. The amp powers up and idles fine.
OUTPUT FETS?
Originally, a IRF3710 output had blown and damaged the board location. The owner bought 1 and installed it into the empty location next to the other output in the same bank. The amp has output and plays normally until the volume is increased and then the amp cuts out and turns back on. If left to play at low volume, the amp continues to play without interruption.
OUTPUT IC?
The HIP4080 was not changed when the output was damaged and is still in the amp playing.
POWER SUPPLY FETS?
Six of the PS FETS were blown. 2 sets of three, each set from one side of each transformer. I took the good originals from one transformer and put them to complement the other originals on the other transformer. I then installed six recycled 70N06 FETS to the two banks of the remaining transformer. The amp powers up and idles fine.
OUTPUT FETS?
Originally, a IRF3710 output had blown and damaged the board location. The owner bought 1 and installed it into the empty location next to the other output in the same bank. The amp has output and plays normally until the volume is increased and then the amp cuts out and turns back on. If left to play at low volume, the amp continues to play without interruption.
OUTPUT IC?
The HIP4080 was not changed when the output was damaged and is still in the amp playing.
When I went to test for no load shutdown I discovered that the cast metal terminal for the remote was broken. I restored that connection and now the amp is remaining on and no longer cutting off like it was before.
What is happening now is that the output is clipping when turned up to a moderate level. The amp not cutting off leads me to believe that the PS FETS are functioning normally.
Is the output clipping likely to be coming from the outputs or from the HIP4080? How can I test for the cause other than just changing them all?
What is happening now is that the output is clipping when turned up to a moderate level. The amp not cutting off leads me to believe that the PS FETS are functioning normally.
Is the output clipping likely to be coming from the outputs or from the HIP4080? How can I test for the cause other than just changing them all?
Thanks for the effort. I have gotten into the habit of "select all" and "copy" all the text of my responses before I submit reply. Losing all of that typing has frustrated me too many times before...
I am actually calling it "clipping", but what is happening is that the bass in the subwoofer plays clean at low levels and remains clean up until a point just before it gets loud and then it distorts in bursts. It stops if I turn the volume back down.
This testing was done in the car so the only tool I had was a multimeter. I inserted the probes into the + and - speaker terminals and turned it to DC voltage. When the music is playing cleanly I get a continuous reading around 0.30, but whenever the distortion burst comes through, the display changes but it happens so fast that I don't get an actual reading. The little - sign appears whenever it happens while the red probe is on positive terminal and black on negative. I reversed them and the - sign didn't appear when the display changed but it still didn't give me an actual numeric reading since it happens so fast, and I don't push it any harder for fear of damaging the speaker or amp.
I am actually calling it "clipping", but what is happening is that the bass in the subwoofer plays clean at low levels and remains clean up until a point just before it gets loud and then it distorts in bursts. It stops if I turn the volume back down.
This testing was done in the car so the only tool I had was a multimeter. I inserted the probes into the + and - speaker terminals and turned it to DC voltage. When the music is playing cleanly I get a continuous reading around 0.30, but whenever the distortion burst comes through, the display changes but it happens so fast that I don't get an actual reading. The little - sign appears whenever it happens while the red probe is on positive terminal and black on negative. I reversed them and the - sign didn't appear when the display changed but it still didn't give me an actual numeric reading since it happens so fast, and I don't push it any harder for fear of damaging the speaker or amp.
The owner performed the first repair. One output had blown up and he simply replaced it. It played for a minute he said and then one of the rail caps vented electrolyte onto the board. Half of the power supply was blown so I moved the 6 remaining ps FETS to one Transformer and installed 6 used matching FETS to the other Transformer. I replaced the blown resistor that was between the primary and secondary grounds. The outputs and output IC are the ones that were in the amp when it went down the last time.
I will try it at 4 ohm and see if there is a difference. I had been testing at 1 ohm since it sounds so weak at 4 ohms and the owner plays it with a 1 ohm load.
I will try it at 4 ohm and see if there is a difference. I had been testing at 1 ohm since it sounds so weak at 4 ohms and the owner plays it with a 1 ohm load.
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