Lanzar MXA 282

S Merlington · 2012-12-31 1:03 am

Got another one of theese in with the same problem..

Amp stsys in protection mode ..

If i remove all of the outputs from the right channel amp will power up and produce clean audio from the left channel..

I replaced every transistor in the right channel put new outputs in it and amp will be stuck in protection mode..

If i remoe all outputs from right channel it will power up

Any ideas??

Perry Babin · 2012-12-31 2:24 am

Check the emitter/source resistors.

S Merlington · 2012-12-31 3:00 am

All check fine ..

They measure 0.5 ohms

Perry Babin · 2012-12-31 3:10 am

Is there a pulse of DC on that channel as you power up the amp?

Post a photo of the board.

S Merlington · 2013-01-01 1:44 am

Yes i get 0.97 volts on the right channel

The pics are of the other one i have but its the same amp

Perry Babin · 2013-01-01 1:56 am

Can you disconnect the preamp board to see if it will power up?

Does the amp draw excessive current when it attempts to power up?

S Merlington · 2013-01-01 1:59 am

amp does same thing with the preamp board disconnected

Amp doesnt draw excessive current when trying to power up

Perry Babin · 2013-01-01 2:02 am

If you bypass the protection circuit, does the amp draw excessive current?

S Merlington · 2013-01-01 2:14 am

how do i disable the protection ?

Perry Babin · 2013-01-01 2:25 am

Which pin of IC 3 is high?

S Merlington · 2013-01-01 2:29 am

Pin 2:12.33
Pin 3:6.59

Perry Babin · 2013-01-01 2:48 am

I'm using a different amp as a reference (the photos posted weren't of high enough resolution). IC 3 is the IC next to the 494. Pins 1 and 7 are the outputs. If those voltages were from pins 1 and 7, post the DC voltage on all pins of that IC.

S Merlington · 2013-01-01 2:51 am

yes IC3 next to the 494

Pin 1:0.00
Pin 2:12.36
Pin 3:6.60
Pin 4:0.00
Pin 5:11.53
Pin 6:4.96
Pin 7:11.60
Pin 8:13.17

Perry Babin · 2013-01-01 3:12 am

If the cathodes of D6 and D7 are directly connected, lift D6. That should disable the protection circuit.

S Merlington · 2013-01-01 3:21 am

With D6 lifted amp powers up and idles perfectly..

I get 51 volts on the right channel measured directly across the speaker terminals

Perry Babin · 2013-01-01 3:27 am

There may be multiple problems. With that much DC, the differential amp should be driving the amp to draw current as it tries to eliminate the DC. Since it is not, either the differential amp circuit is damaged, there is a shorted driver or both. There are other possibilities but those are the most likely.

S Merlington · 2013-01-01 4:02 am

So IC 3 may be defective?

Heres what i get when the amp is powerd up on IC3

Pin 1:0.00
Pin 2:12.36
Pin 3:6.60
Pin 4:0
Pin 5:13.16
Pin 6:4.96
Pin 7:11.95
Pin 8:13.16

Perry Babin · 2013-01-01 4:19 am

I don't see a problem with IC3. It appears that pin 5 is being driven high by the fault in the defective channel and that was preventing the amp from powering up.

S Merlington · 2013-01-01 4:23 am

Guess i will check everything in that channel since i put new driver ic's in it also all outputs test fine and still same problem

S Merlington · 2013-01-02 2:06 am

I found that the Drivers (TIP31C and TIP32C) for the outputs have 53 volts on all 3 legs ..

I started removing 1 transistor at a time to get rid of the 51 volts on the legs of the drivers..

i think a few are defective..

anyone know if there are any good subs for theese??

C2229
A970

I have some C2235's on hand wondering would thoose be a good sub for the C2229 or not?

Lanzar MXA 282

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