This amp has a stange issue..
Amp will power up and play fine but if i try to increase the gain past 1/4 of the way the will go in and out of protection..
Any ideas?
Amp will power up and play fine but if i try to increase the gain past 1/4 of the way the will go in and out of protection..
Any ideas?
Amp has low output so if u try to increase gain over 1/4 amp will protect if I even touch the gain or cross over pots the amp will protect..
Any ideas what might cause this?
Any ideas what might cause this?
Perry Babin has some tutorials on gain pots that might be helpful. Not sure these can be tigthened up, normally we replace with new pots. PM me if you can't get pots fixed.
If you will post a pic of main board top and bottom and close up of preamp board. There may be other problems such as a burnt trace on preamp or bottom side of main board. Also, bad solder on the bottom side of main board.
If you will post a pic of main board top and bottom and close up of preamp board. There may be other problems such as a burnt trace on preamp or bottom side of main board. Also, bad solder on the bottom side of main board.
Ok sorry the board is green in this amp..
I disabled the protection in the amp to see what the amp does without going in protection..
I dont believe its the pots at all..
Amp will play a few secs the the output becomes very distorted and the output level decrese's by half..
The amp will play very distorted output sounds like tin cans then go back to normal then go back to distorted out over and over..
Any ideas on where to start?
I disabled the protection in the amp to see what the amp does without going in protection..
I dont believe its the pots at all..
Amp will play a few secs the the output becomes very distorted and the output level decrese's by half..
The amp will play very distorted output sounds like tin cans then go back to normal then go back to distorted out over and over..
Any ideas on where to start?
Have you examined the preamp board for burnt traces or broken RCA'S? There may be burnt traces on the bottom side. Also, make sure the grounding screw is in place and there is zero ohms between screw and hold down bars. At the moment it sounds like a grounding issue.
Yes i have a scope..
The ground wire reads 0.04 ohms between it and the clamps..
Lifting Q04 disables the protection correct?
The ground wire reads 0.04 ohms between it and the clamps..
Lifting Q04 disables the protection correct?
Q04 should work,although you might try replacing Q04 and lifting R22, This will determine if the protection is caused by something in the output which I suspect it is.
Check to see if you have a triangle wave @ U124-Pin 4 and Square wave w/ 50% duty cycle @ U124-Pin 11 and measure the frequencies of both. Also, measure the DC voltages of U124-Pin 8 & 11,black probe on negative speaker terminal and post results.
Check to see if you have a triangle wave @ U124-Pin 4 and Square wave w/ 50% duty cycle @ U124-Pin 11 and measure the frequencies of both. Also, measure the DC voltages of U124-Pin 8 & 11,black probe on negative speaker terminal and post results.
PIN 4 of U124 i get a triangle wave
Pin 11 of U124 i get a square wave..
Lifting R22 make the audio still cut in and out but amp doesnt protect..
PIN 8:2.87
Pin 11:0.49
Pin 11 of U124 i get a square wave..
Lifting R22 make the audio still cut in and out but amp doesnt protect..
PIN 8:2.87
Pin 11:0.49
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I meant to say U124 Pin 10, you should see approximating -2.00 considering all else looks normal I expect that's what you will find.The triangle wave should be sharp and linear slopes.and the square wave on Pin 11 is approximately 50%.In other words equally on and off.
Check the Vdc across the outputs.Carefully, probe from the outside to outside leads, for at least one mosfet (IRF640 & IRF9640) in each bank.I suspect that these are good, but it's important to establish the operation of the amp itself. I'm inclined to believe that the problem is a grounding issue. (burnt trace, broken RCA's, cracked or leaky caps). I still not ready to rule out bad Pot's.
Check the Vdc across the outputs.Carefully, probe from the outside to outside leads, for at least one mosfet (IRF640 & IRF9640) in each bank.I suspect that these are good, but it's important to establish the operation of the amp itself. I'm inclined to believe that the problem is a grounding issue. (burnt trace, broken RCA's, cracked or leaky caps). I still not ready to rule out bad Pot's.
The triangle wave on pin 4 looks like it should..
The square wave on pin 11 looks as it should equally on and equally off
PIN 4 and Pin 10 voltages are: Using speaker terminal ground
Pin 4:-0.03
Pin 10:-1.90
IRF640 Red prob on gate leg black probe on source leg i get :3.46
IRF9640 Red probe on gate leg Black probe on source i get: -3.91
Ive ruled out the pots as i found another preamp board from a working amp and swapped them to see it the pots were the problem amp still cuts on and off with a different preamp board installed..
Ive looked for broken traces but find nothing also the ground seems to have a solid connection also..
The square wave on pin 11 looks as it should equally on and equally off
PIN 4 and Pin 10 voltages are: Using speaker terminal ground
Pin 4:-0.03
Pin 10:-1.90
IRF640 Red prob on gate leg black probe on source leg i get :3.46
IRF9640 Red probe on gate leg Black probe on source i get: -3.91
Ive ruled out the pots as i found another preamp board from a working amp and swapped them to see it the pots were the problem amp still cuts on and off with a different preamp board installed..
Ive looked for broken traces but find nothing also the ground seems to have a solid connection also..
Check the Vdc on all 5 pins on the preamp board, black probe on -spkr terminal and post. Also,with your scope look at the Out pin on the preamp board with and w/o signal applied.
Underneath the preamp board you will find C219 (10uf/160V BP). I'm not sure about this amp. but on other amps, the leads from the pots sometimes cut into the capacitor and will cause the amp to oscillate and feedback into the signal path,which would cause the amp to cut in and out. If this is the case you may need to replace the cap, trim the leads. There may be a piece of insulation (plastic or cardboard) stuck to cap. Replace if necessary.
Underneath the preamp board you will find C219 (10uf/160V BP). I'm not sure about this amp. but on other amps, the leads from the pots sometimes cut into the capacitor and will cause the amp to oscillate and feedback into the signal path,which would cause the amp to cut in and out. If this is the case you may need to replace the cap, trim the leads. There may be a piece of insulation (plastic or cardboard) stuck to cap. Replace if necessary.
Replaced C216 under the preamp board same thing amp goes in and out of protection..
Preamp board voltages on all 5 pins are
+12 :11.95
GND :0.00
-12 :-12.30
V.C :-11.02
Out :0.00
The signal on the out pin looks good with signal applied also doesnt do anything without signal applied so thats good there
Preamp board voltages on all 5 pins are
+12 :11.95
GND :0.00
-12 :-12.30
V.C :-11.02
Out :0.00
The signal on the out pin looks good with signal applied also doesnt do anything without signal applied so thats good there
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