A buddy gave me his 1501d to work on and says that it will not power on.I got it home checked out the fets and haven't found anything to be bad.I decided to try and power it up through a 3 amp fuse.The amplifiers power light came on for a moment and then the fuse blew.Is it possible that my fuse is too small?Does this amp pull more amperage than that upon turn on?
You may need to use a 15 amp fuse to power up this amp. The transistors must be clamped down tightly to prevent damage in case there is another problem.
There is an LED in the center of the rail caps. Do not handle the board until the LED has gone completely dark. The rail capacitors store a lot of energy and can be dangerous. If it takes more than 20 seconds for the LED to go dark, the discharge circuit may be defective. In that case, you will have to repair the discharge circuit or discharge the capacitors each time you remove power from the amp.
There is an LED in the center of the rail caps. Do not handle the board until the LED has gone completely dark. The rail capacitors store a lot of energy and can be dangerous. If it takes more than 20 seconds for the LED to go dark, the discharge circuit may be defective. In that case, you will have to repair the discharge circuit or discharge the capacitors each time you remove power from the amp.
It's not likely that those are causing any problems at this point. They are connected between chassiis ground and shield ground. The diode with the striped end connected to the shield burns when the chassis ground for the amp is lost and the amp tries to ground through the RCA shields. In the later model amps, they left that diode out of the circuit to prevent this from happening.
If the diodes are shorted, you'll have to remove them to determine which pads are connected to the shield.
If you get it working, you need to solder the shield on the RCA jack to the RCA jack housing/frame. They get loose and destroy speakers when the shield ground is lost (due to the bad connection between the shield and the frame).
If the diodes are shorted, you'll have to remove them to determine which pads are connected to the shield.
If you get it working, you need to solder the shield on the RCA jack to the RCA jack housing/frame. They get loose and destroy speakers when the shield ground is lost (due to the bad connection between the shield and the frame).
I just finally got around to powering this thing up with a larger fuse.Using a 10 amp fuse i powered it up and it did not blow but the amp will not turn on and stay on.It turns on for a second then turns off then turns on again and makes a humming noise and turns off.After it repeats that a couple times the led in the center of the rail caps turns on followed by another led thats next to all the rail caps that blinks while the amp makes a sound almost like a warning buzzer of some sort.Never seen anything like this.It takes quite a while for the led in the center of the rail caps to go completely dark as well.
Is the voltage on your DC power supply dropping significantly when the amp tries to turn on?
LED238 will illuminate as the amplifier comes out of muting and the drive circuit is activated. If it senses a problem like over-current, the amp will go into protect and the LED will go off.
Is there any DC across the positive an negative speaker terminals before LED238 comes on?
LED238 will illuminate as the amplifier comes out of muting and the drive circuit is activated. If it senses a problem like over-current, the amp will go into protect and the LED will go off.
Is there any DC across the positive an negative speaker terminals before LED238 comes on?
I just jumped back into this thing for the first time in a long time.I recently got a power supply so I decided to try to power this thing up again.Upon applying remote power this thing maxed out my 25 amp supply and sent it into protect for a split second.It killed a 15 amp fuse instantly and a 20 amp fuse just barely survived.After the inital inrush of current the amp settles back down to around one amp until the it comes out of muting and then it sits right around five amps with no load or signal attached .The amplifier does remain powered up through the whole process but the transformer(or something near it) is making a horrible humming noise.I was looking closer today at the power input caps ( 35 volt 8200 mfd) and I noticed that plastic sleeve on them has burnt through to the metal on teo of the three.There are also some small square yellow caps near the power input caps that looked blackened as well.Is it possible that these caps are shorted and or out of tolerance and causing the spike in amperage at power up?
The damage to the caps appears to be superficial. The yellow caps are blackened from the failed power supply FETs.
These amps draw a lot of current on startup. 5 amps is more idle current than I'd expect.
Do the inductors near the speaker terminals get hot quickly?
Do any of the caps near the speaker terminals get hot?
Do any of the heatsink mounted components produce enough heat to make the heatsink get warm or hot if you leave it powered up for 10-15 minutes?
These amps draw a lot of current on startup. 5 amps is more idle current than I'd expect.
Do the inductors near the speaker terminals get hot quickly?
Do any of the caps near the speaker terminals get hot?
Do any of the heatsink mounted components produce enough heat to make the heatsink get warm or hot if you leave it powered up for 10-15 minutes?
Do you think that the yellow caps are ok as well?or should they be replaced?I just powered the amp on for approximately 15 minutes.The inductors and the caps all got fairly warm after 15 minutes although they never got so hot that they couldn't be touched with a bare hand . I measured about 135 degrees f on the outside of the caps and about 150 degrees f directly on the top of the inductors. The caps and inductors heated up gradually though. The only part of the heatsink that really got warm at all was near the output fets and they only warmed up maybe ten degrees in the fifteen minute span.
The yellow caps look like they have soot on them but I can't see any defects in the photos. You can clean them with acetone to see if the black coating is superficial.
The output caps shouldn't have been that warm. Were all 4 the same temperature?
It may be difficult to troubleshoot this without a scope. What make/model multimeter do you have?
Does it look like the output transistors have been replaced?
If so, what is the number on the transistors?
The output caps shouldn't have been that warm. Were all 4 the same temperature?
It may be difficult to troubleshoot this without a scope. What make/model multimeter do you have?
Does it look like the output transistors have been replaced?
If so, what is the number on the transistors?
The blackened areas appear to be just dirt/soot. All 4 of the output caps were approximately the same temp.A couple of them have bulging tops.My multimeter is just a cheapie they gave me at work Its an extech EX411.Nothing special but its true rms and has a temperature setting which comes in handy.the output fets appear to be original.They are FB42N20D. A couple of the power supply fets look like they may have been replaced as the solder looks different from others in the amp.The power supply fets are fairchild parts 75339P.
The top of the caps may look like they are bulging when it's just the plastic cover that's being pushed up because the shrink wrap is squeezing in on it. Try pushing it down. If it goes flat and then pops back up, it's nothing to be concerned about.
Is LED238 brightly lit and steady on?
Does the amp produce audio?
Is LED238 brightly lit and steady on?
Does the amp produce audio?
I checked the amp for audio after work today.I just ran a sine wave through it first and tested it with my meter to see if there was any ac voltage present and there was.I also decided to see if there was any dc voltage present on the output terminals and at first I had 2 volts.The more i played with the gain and bass boost the higher i was able to get the dc voltage.It wasn't constant voltage,it would just spike whenever i adjusted the gain or bass boost. At times it would get close to 20 volts.Next I unhooked the rcas and tested for dc and ac.Again there was dc voltage present around 2 volts.Also when the rcas are unhooked there is 70 volts ac present on the speaker outputs.
If there is DC voltage on the output that varies with the gain, the THAT 2155 voltage controlled amp (near the RCA jacks) is probably defective. I've never seen this in the 1501 but I've seen it quite a few times in other MTX amps.
I'm not sure why you had 70v AC on the output without the RCAs connected. This could be the reason for the high idle current and the warm output filter caps. Is the idle current less with the RCAs plugged in but no speakers connected?
If you disconnect all wires/cables from the amp, what is the resistance from the input shield to the ground terminal of the amp?
I'm not sure why you had 70v AC on the output without the RCAs connected. This could be the reason for the high idle current and the warm output filter caps. Is the idle current less with the RCAs plugged in but no speakers connected?
If you disconnect all wires/cables from the amp, what is the resistance from the input shield to the ground terminal of the amp?
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