I half took this amp apart and I forgot where the PS driver transistors are supposed to go. Its hard to dead all the descriptions on the PCB because a transformer coil is covering with glue, but I beleive they are Q7, Q7R, Q8, and Q8R.
Originally, this amp had either an A1275/C3228 or A1274/C3227 combination but I cannot remember which, or what parts I can use as better installation. I have a lot of MPSA06/56 but I'm also putting togeth an order at Mouser. Which would be the best combo for this style of amp? I fix a lot of these for one of my customers.
Thanks!
Originally, this amp had either an A1275/C3228 or A1274/C3227 combination but I cannot remember which, or what parts I can use as better installation. I have a lot of MPSA06/56 but I'm also putting togeth an order at Mouser. Which would be the best combo for this style of amp? I fix a lot of these for one of my customers.
Thanks!
OK I replaced the PS driver transistors with BD139/BD140. The BD140s ended up in the furthest possitioned components from each other. The amp does the same thing. When powered on, the PS fets get hot within seconds. The waveform on the fet gates while the fets are installed quickly goes from about a +8v square wave down to about a +4v square wave.
I pulled the rectifiers because I thought they were measuring up in-correctly, but then realized they are AC Doubler type diodes similar to the schematic listed as "Suffix D" in this datasheet:
http://www.fairchildsemi.com/ds/FE%2FFEP16DT.pdf
I'm not really too sure why amp is acting like this.
I pulled the rectifiers because I thought they were measuring up in-correctly, but then realized they are AC Doubler type diodes similar to the schematic listed as "Suffix D" in this datasheet:
http://www.fairchildsemi.com/ds/FE%2FFEP16DT.pdf
I'm not really too sure why amp is acting like this.
I should also mention, the PS fets were all dead in this amp, so I installed one IRF3205 into each bank with 47ohm gate resistors. Q13 and Q18. Q18 is getting much hotter and quicker than Q13, but the waveforms are still bad on both Q13/Q18 while IRF3205s are installed. Removing the IRF3205s and I get a nice +10v square wave on the gates.
After pulling the rectifiers, the power supply fets still get hot after seconds.
After pulling the rectifiers, the power supply fets still get hot after seconds.
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Referencing amp ground;
With the fets removed and the scope set to 5v/Div and 10uS:
With one fet installed, the waveform is not solidly defined, starts at about +8v Square and drops do +5v Square.
I posted a very short video (<10 second video) of the action/change on the scope here. At ~3 seconds I power the amp, and then the waveform drops to ~5v I power the amp off to protect the fet.
mtx :: VID_20110425_182356.mp4 video by unclemeat2010 - Photobucket
With the fets removed and the scope set to 5v/Div and 10uS:
With one fet installed, the waveform is not solidly defined, starts at about +8v Square and drops do +5v Square.
I posted a very short video (<10 second video) of the action/change on the scope here. At ~3 seconds I power the amp, and then the waveform drops to ~5v I power the amp off to protect the fet.
mtx :: VID_20110425_182356.mp4 video by unclemeat2010 - Photobucket
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R30/R31 are connected to the Collectors of the drivers (Center leg).
The Base of the drivers are Leg #3 which are connected to the 3.3k resistors. Also from the base, resistance of 470 ohms is measured to Pin 9/10 of the driver IC which is a KA7500BD. Pin 9/10 of the KA7500BD are measuring 210 ohms to ground.
The driver emitters are leading to the Fet gate/resistors.
From where you are directing me, it sounds like the drive circuit isnt meant to handle the IRF3205s, and we're now trying to modify the circuit to handle the IRF3205s. If that is the case, I tried putting an FQP50N06 in place of the IRF3205 and it too got hot after seconds with 47ohm gate resistors.
The Base of the drivers are Leg #3 which are connected to the 3.3k resistors. Also from the base, resistance of 470 ohms is measured to Pin 9/10 of the driver IC which is a KA7500BD. Pin 9/10 of the KA7500BD are measuring 210 ohms to ground.
The driver emitters are leading to the Fet gate/resistors.
From where you are directing me, it sounds like the drive circuit isnt meant to handle the IRF3205s, and we're now trying to modify the circuit to handle the IRF3205s. If that is the case, I tried putting an FQP50N06 in place of the IRF3205 and it too got hot after seconds with 47ohm gate resistors.
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I traced pin 9/10 of the driver IC and they lead to pins 8 & 9 of the 11 pin driver board (4th and 3rd pin from the right). Pin 8 leads to R31 (Left 220 ohm resistor) and Pin 9 leads to R30 (Right 220 ohm resistor). From these resistors, the trace leads to Leg 2 (Center leg) which should be the BD140s' collector.
When powered with a fet installed, Pin 9/10 of the driver IC post defective waveforms as previously posted. I also now know that part of the problem is ending up dragging my power supply to the point where it drops from 13.8vDC down to ~10vDC.
When powered with a fet installed, Pin 9/10 of the driver IC post defective waveforms as previously posted. I also now know that part of the problem is ending up dragging my power supply to the point where it drops from 13.8vDC down to ~10vDC.
Yes
Yes
I do as long as the Fets are removed. With them in place the signal fades like the previous video posted.
I took a walk and came back, and now notice that it is not the 1k/220ohm resistors I replaced driving the base of the driver transistors, but a pair of 510ohm resistors at R60 and R60A. I should go back to the 1K resistors for R30/R31. Shouls I try 220 ohm resistors in place of the 510ohm ones?
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