Zero Cool

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About Zero Cool

  1. I'm going off memory, but the MA2400 i believe is very similar to the MA3600 i am working on now. when the power switch is pressed, it starts the fan/former which supplies power to the front end of the amp. once that comes up and everything is ok, then it kicks on the relays which are in the primary circuit of the power transformers. this then supplies power to the output sections of the amp. I have seen situations where the AC outlet has a loose connection. when the transformers kick on, there is an initial surge as the transformers and cap banks energize. If that AC connection is loose, it can cause the AC line to drop enough to kick the relays back off, or buzz as you described. also, the ac line goes through circuit breaker(s). it is possible they are weak or broken causing a low line voltage situation. The push on connectors on the soft start board could be loose or corroded. I would go through everything from the incoming power cord right to the transformers and check the connections. I would also check all the connections within the amp and to the soft start board. Just my thoughts
  2. Have you replaced MC3408?? do you see the noise before the opamp, you should be able to find the datasheet online and figure out which is the input that feeds the output on pin 7, see if you see the noise before the opamp. I have had opamps make noise, have dc offset, oscillate, be unstable do all sorts of odd things in various amps. In fact i just fixed and amp that at low levels worked great, but once the opamp in the input side got to a certain output level it would turn into an AM transmitter and oscillate like mad making a horrendous noise at the output of the amp. replacing the opamp cured the problem!
  3. Lots of questions here. 1- does your crossover sum the L+R channels together for the sub outputs? if not then you will only get one channel of sub lows to your bridged crown amp. you can test this by connecting one sub out to the amp and then adjust your balance control. if you connect it to say the left sub out of your x-over and you pan right, does the subs go away? If they do, then you will need to find a way to mix the L+R sub outs together. just connecting both together with a -Y cord is not recommended. you will need some form of a small mixer or a passive resistor summing network to combine L&R sub signals together into a mono amplifier. Yes you can run the input level control wide open if you need to without harm. If you are using this amp with home audio components do you set the internal level control switch to .775V??? this will make the amp a bit more sensitive and you may not need to run the volume control all the way up. generally more signal to the amp is better within reason and as long as that signal is clean and doesn't distort before it gets to the amp.
  4. P.S. Can i use a IRF630 Mosfet in place of the MTP7N20E??? the specs look very close. both 200V, the MTP is 7 amp, the IRF is 9 amp, RDS for both is .4ohm, the gate capacitance of the IRF is a bit more but i don't know if that will matter in this application as a pass device? Zc
  5. Excellent! Thank You, I will replace C23 & C24 as well then! Yes i have the service manual and have been reviewing it carefully. I have repaired many many amplifiers previously but this is my first full switching amp and i am proceeding cautiously. In reviewing the failure. Any ideas of what would have caused D3, Q2, Q6 to fail?? Q6 i cant quite tell if something came in contact with the Cathode and Anode leads or if it arced over and thats what caused the marks on the leads. It sure looks like arc over upon examination under a microscope but i cant tell for sure. Is this a common failure that i should stock parts for? Thank You Very much! Dave Meyers Overkill audio inc. AKA Zero Cool
  6. I am kind of disappointed that i haven't got a response yet to these post's. But, I managed to scrounge enough test parts to replace D3, Q2, Q6 and F1 and lo and behold the amp came back to life! So now i need to locate the exact replacement parts to finish the amp.
  7. I found D3 is shorted and Q6 the SCR looks as it something came in contact with 2 of the leads. the SCR still works but it is possible something bounced around inside the chassis and shorted the SCR out. I dont see anything in the chassis but it is possible it has fallen out already. I am going to replace Q6 and D3. I am questioning if the Mosfet Q2 is any good. it doesn't appear to be shorted. but measuring the resistance from lead to lead shows to lower resistance then what i would expect so i am going to replace it as well. I don't see anything else in the immediate area that is bad or measures bad. I am concerned however that i have plugged and unplugged various cables and i don't know if the power supply had ever been discharged. I followed the procedure but if Q6 was bad it may not have discharges the caps... I am wondering if i can use a current regulated power supply set for 1amp or maybe a little less to inject +15 volts after F1 to see if i can power up the 125Khz stage without wasting more 1 amp fuses. The current regulated supply should fold back if there is still a problem i haven't located yet. Or...Is there another way to isolate and trouble shoot this portion of the amp??? I spose it could be possible to use a test bulb of some sort in place of F1 to limit the current should there still be a problem.... Please Advise Zc
  8. Hello, I am a tech working on an K2 amp that has blown the Internal 1 amp Fuse F1. The transformer came lose and had moved around a bit pulling on the secondary leads causing the quick connect terminals to loosen up. this may have been the original cause of the problem. Replacing F1 with an external fuse causes the amp to flicker on for a second before it blows the fuse again. So something on that 15V rail is causing the problem. I need to dig into it further now that i have studied the service manual and schematics a bit. Any trouble shooting advice for such an issue. any common failures to look for etc. Of note, the service manual states F1 is a 3 amp fuse??? but it is clearly marked 1 amp on the pico fuse itself. (the service manual also has a type-o in the description of the circuit as it states R6 and the schematics shows R5....) I am assuming that this is just a typo in the manual? and that the installed part and the parts list are actually correct. Zc