MTX 81001

S Merlington · 2013-03-10 4:55 am

0.2 ohms

Perry Babin · 2013-03-10 5:04 am

Do you see a square wave on pin 2 of one 3120 and pin 3 of the other 3120?

Set you scope to 2v/div and about 5us.

S Merlington · 2013-03-10 5:10 am

Perry Babin · 2013-03-10 5:12 am

If you touch a speaker or dummy load across the speaker terminals, does the amp draw current or does the voltage drop to 0v?

S Merlington · 2013-03-10 5:23 am

The voltage drops to 0.02

Perry Babin · 2013-03-10 5:35 am

Does it immediately go back up when you remove the load?

I'm assuming that the current draw didn't change when you applied the load. Is that correct?

S Merlington · 2013-03-10 5:37 am

current draw remains the same never went up..

As soon as i remove the load the voltae goes back up immediately

Perry Babin · 2013-03-10 5:51 am

Have you confirmed that both opto-couplers have good supply voltages?

Black on pin 5, red on pin 8, do NOT let the probes slip.

S Merlington · 2013-03-10 5:58 am

ON 1 i get 18.31 volts

On the other i get 15.51 volts

Perry Babin · 2013-03-10 6:12 am

Have you replaced the 5532 nearest the 3120s after the last failure of the 15v regulator?

The input offset is a bit more than I'd expect. It may be OK if the amp was oscillating but I'd expect it to be closer with no oscillation.

Connect a load to the speaker terminals and post the DC voltage on pins 5, 6 and 7 of the 5532 nearest the 3120s.

Confirm that the voltage without the load is the same as the voltages you previously posted for pins 5, 6 and 7.

S Merlington · 2013-03-10 6:20 am

Havent replaced the 5532 yet..

with no load the voltages are

Pin 5:0.66
Pin 6:1.52
Pin 7:0.99

With a load the voltages are

Pin 5:0.00
Pin 6:0.02
Pin 7:0.02

So should i replace both op-amps and see what i come up with??

Perry Babin · 2013-03-10 6:26 am

It appears to be defective.Replace the one nearest the 3120s at least.

S Merlington · 2013-03-10 6:40 am

Ok replaced the one nearest the 3120's the voltage on the output terminals is 0.04 volts now...

LED 400 is still lit

Perry Babin · 2013-03-10 6:41 am

Do you see oscillation on pin 2/3 of the 3120s?

LED400 is supposed to be lit.

S Merlington · 2013-03-10 6:44 am

yes i see oscillation on pins 2/3

Perry Babin · 2013-03-10 6:45 am

Was the preamp board ever in the circuit when the regulator was producing too much voltage?

S Merlington · 2013-03-10 6:46 am

not since i got the amp dont know about before i got it im assuming it was pluged in before i got the amp..

Perry Babin · 2013-03-10 6:50 am

I'm trying to determine if it's likely to have damage. Was the regulator damaged when you got the amp?

Do you have any shunts like those used on computer headers or old hard drives?

S Merlington · 2013-03-10 6:51 am

The regulator was defective when i got the amp..

I have shunts from and old hard drive

Perry Babin · 2013-03-10 6:54 am

Install 2 as shown below. Do you have audio with the jumpers in place?

MTX 81001

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