SPL ZX1-3000D

brandes.cm · 2011-09-17 3:14 am

I see it now.
What could cause my fuse to blow after sitting idle for 30 seconds.

Perry Babin · 2011-09-17 3:16 am

What size fuse?

Is anything getting hot?

brandes.cm · 2011-09-17 3:39 am

It was a 10 amp fuse.

The only thing getting warm is R361 R362, 4,7K. They tie to +-rail.

Perry Babin · 2011-09-17 3:53 am

I'd suspect a bad driver or an intermittently shorted output inductor.

brandes.cm · 2011-09-17 3:58 am

Another question deals with the input signal. what should I reference when trying to follow the signal through.
If I hook the probe ground to the incoming rca ground I can follow the signal through the first two op-amps. Should I be able to reference the power supply ground. RF amps have a 1K between chasis and circuit common, this amp must not have it? I find no other gnd spot in this amp for the input circuit.

Perry Babin · 2011-09-17 4:04 am

The RCA shield should be tied to the secondary center tap and the negative speaker terminal. Using any of those as the reference should work. The signal should be easy to follow through to the input pin of the driver board. The exception may be through the 13600 IC. If the other ICs have excessive DC on their output pins, there may be a problem with the op-amp.

brandes.cm · 2011-09-17 4:25 am

R101 ties the rca shield to the center tap. That resistor was burned when I got the amp, I replaced it with a 220ohm. I believe you told me the value.

Perry Babin · 2011-09-17 4:31 am

That's a low enough resistance that there shouldn't be a problem with using the shield as the reference. Is there any significant voltage between the negative speaker terminal and the RCA shield when the amp is on.

brandes.cm · 2011-09-17 4:41 am

I believe the second op-amp in has a bad stage. I have a signal on pin 1 but 5,6,7 all sitting negative.
Would a TL072 work for a replacement?

Perry Babin · 2011-09-17 4:45 am

Is the master/slave switch set to master?

brandes.cm · 2011-09-17 4:54 am

It is now, still no signal on pins 5,6,7

Perry Babin · 2011-09-17 4:56 am

Are they at 0v now instead of negative?

brandes.cm · 2011-09-17 5:03 am

Yes, with a slight pulse going neg. I mean really slight.

Perry Babin · 2011-09-17 5:06 am

Set the gain to the max position. Does it stop or rotate round and round?

At the max position, do you see output on pin 7?

brandes.cm · 2011-09-17 5:11 am

I adjusted the gain full, it does stop. I now have my signal at the speaker terminals. What makes the gain kill the signal, resistor value out of tolerance?

Perry Babin · 2011-09-17 5:22 am

The signal wasn't likely completely lost. Did you check the signal on the speaker terminals between the time when you set the switch to master and the time when you set the gain higher?

brandes.cm · 2011-09-17 5:39 am

I did, but I wouldn't doubt it was a scope adjustment error from me.

I had the amp running a few minutes with a signal when the neg. side fets got warm and blew the fuse.

I swapped the output fets; originals were FB31N20 with FQP32N20. This was a Fairchild cross. I should check the gate signal for a slow rise and fall time?

Perry Babin · 2011-09-17 5:43 am

I don't know what to suggest. When making substitutions, you need to get the amp working properly with the original parts and then try the subs.

Why not use the original part?

brandes.cm · 2011-09-17 5:47 am

The originals were all shorted.
I will look for originals and replace my subs if possible.

thanks again.

Perry Babin · 2011-09-17 5:51 am

Buy them from a reputable distributor. There are a lot of fake ones being sold (particularly on ebay).

SPL ZX1-3000D

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