lanzar 50c problems

[67elcamino]

i have an old optidrive 50c didnt work when i bought it. now i have replaced the power supply fets and it still dont power up. infact it acts like a dead short when i hook up power as it did before i replaced the fets. it will blow any fuse instantly. hoping someone could help with this. i would also like to know what the original fet part #s are for this amp. thanks

[Perry Babin]

Does it blow the fuse with no remote voltage applied?

Are the power supply FETs shorted? Measure the resistance from leg 1-2. Do any read near 0 ohms? I know you just replaced them but check them anyway.

Have you checked for solder bridges between the legs of the FETs?

Were the original FETs defective?

Did you check the gate resistors?

I thinkIRFZ40s were the originals.

[67elcamino]

i will have to check if the fuse blows without the remote hokked up. its been a year or so since i messed with it. the original fets were bad, they were burned (exploded)!! there is no soldier between the legs i double checked that even tripple checked when i put them in. im no expert on amp repair so im not sure which resistors your talking about. if you could tell me where they are located on the board i could easily check them. i will have to pull out the fets again and check them to see if they shorted when i tried to power it up. i will let you know what i find. i have an old u.s. acoustics usx 1000 (zed) and a hifonics zues 650(zed) im also trouble shooting and trying to locate parts for so it may be a couple days before i get to the lanzar. Thanks a bunch for your help!! i currently purchase parts through mouser electronics and arrow electronics, but they dont always have what i need any suggestions who may have parts for these amps? or a good cross reference site? thanks again,

Trevor

[Perry Babin]

For most common parts, Mouser and Digi-key seem to be the best for small orders.

Has arrow provided good service?

It's best not to use substitute parts unless you absolutely have to. If you can't find the original, post the part you're looking for.

If you can't find the parts at Mouser or Digi-key, use either of the following:
http://octopart.com/
http://www.findchips.com/

If you need help with a different amp, start a new thread.

[I Am An Idiot]

The gate resistors are the resistors that are connected to the left most leg of each of the power supply FETs. There is one resistor per FET. I do not remember the value in that amp, probably 47 ohm or 100 ohm.

[67elcamino]

ok my other amps are a piece of cake to fix so no problems there!! arrow has been a great supplier no problems with them at all!! in fact if they have what i need i buy from them but they dont always have the parts.on my 50c i pulled a couple power supply fets on each side and checked them out of circuit and they were fine so i put them back in and checked the rest. i found one bad fet and had a few spares so i replaced it. now i have isolated the power supply from the amp. luckily the lanzar 50c has small jumpers to remove so you can do that. i checked all the resistors and they are ok. they are all 10 ohm which is silver band then black black brown i think. anyway i tried to power it up today with a 50 amp fuse inline. the amp does not blow the fuse when pos. and neg are hooked up. the thing makes a good spark but im sure thats the caps charging. so when i hooked up the remote wire i got it to turn on, the fan spins and the green l.e.d. turns on but about 2 seconds later the fuse blew. tried a stronger fuse and the same thing happened. if you stand the amp on end with the power wire facing down, the left bank of fets got hot!! real quick!!! but the right bank did not get hot at all. thats where im at in this stage of trouble shooting. i also checked the tip35c and 36c output transistors and they are ok but like i said i have that half of the amp isolated. i found one t0-93 transistor thats is part # 2n4403a that was blown in half. that was on the amp side and not the power side of the amp. but i dont know if it is for the amp or power supply. thanks again,


trevor

[Perry Babin]

Unless the replacement FETs are from the same production batch as the ones in the amp, you can't replace only one FET. For testing, if you have only one defective (rare), remove it. The amp will work with only one missing FET.

Never use anything more than a 20 amp fuse (10-15 amp preferred) when troubleshooting. Larger fuses offer VERY little protection to the components.

You probably have either a defective driver transistor or a leaking power supply FET. Remove and check Q61 and Q63. These are the driver transistors. Do NOT apply power with the drivers out of the circuit.

[67elcamino]

i replaced all of the fets just so they were matching, and i pulled and checked q61 and q63 one of them was bad. replaced both of them and i replaced one of the ones next to it because it was blown in half. now that ive done all that the amp powers up fine. so i hooked up the other end of the board that i isolated. i then put audio through it and, no sound. if i turn the gain all the way up then the speaker pops when a snare or bass sound hits, kind of like a distorted bass sound but at lower levels theres no sound at all. so now that the power supply is up and running somethings wrong on the audio end. i checked all of the tip35c and tip36c transistors and they all seem to be ok. where do i go from here!!? thanks

[Perry Babin]

Do you have ~0 ohms between the RCA shield and the non-bridging speaker terminals (no RCAs plugged in)?

Do you have approximately -15v DC on leg 3 of the muting transistors (Q1 and Q3)?

Do you have ~±15v on pins 4 and 8 of the audio op-amps?

Do you have ~±20v DC on the center legs of the output transistors?

Place the black meter probe on the RCA shields for all voltage measurements.

[67elcamino]

q3 and q1 are -11.6vdc
pin 4 and 8 on op amps are 13.54vdc
center leg on outputs are .06vdc,
thats the tip35c and tip36c outputs. right?
so no voltage there. i also checked the rails before i hooked up the amp side of the circuit board and i had 24vdc now with that end of the amp hooked up i got almost nothing there.
and the ohms on rca sheild to non bridge, are 1.250 ohms with my meter set on 2k.

thanks