Targa TG -18D (MA Audio HK2000d)

[Perry Babin]

Are you still driving a signal into the amp?

Is the input level as high as it was?

Do you have signal reaching the driver board?

Did you do anything to the amp between the last time you had output on pins 7 and 12 and now?

 

[chrisg4]

Yes still driving a strong signal, the output on pin 7 is still present

yes i see the signal on the driver board

i might have installed the outputs after checking those pins, cant recall now...

 

[chrisg4]

below are input pins for output pin 12

pin 4

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pin 5

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[Perry Babin]

Is there significant DC across the speaker terminals?

If yes, does the amp draw excessive current if you connect a dummy load to the speaker terminals?

Are the outputs in the circuit?

 

[chrisg4]

I see -1v on the positive speaker terminal

I don't have a meter to check the current draw

installed a pair fets per side

 

[Perry Babin]

remove the outputs and if there is still more than a tiny fraction of a volt across the speaker terminals, connect a load to pull the voltage as close to 0v as possible.

Do the drive signals return?

To have drive out of the LM319, the voltage on pin 4 must fall between the top and bottom of the triangle waveform on pin 5. Having DC across the speaker terminals is likely what caused the offset on pin 4 of the 319.

 

[chrisg4]

Outputs removed, square wave returns to pin 12

but still no drive on the gate pads of the fets

 

[chrisg4]

Hi Perry,

what should i use to replace Q902, Q903? cant see the marking on them

 

[chrisg4]

While probing the board i shorted the below:

R919 - 15k resistor
zener diode - please help with value of this

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[Perry Babin]

The zener diodes have a DZ or ZD designation. This could be a standard 1N4148 type diode. See if you can find its corresponding diode on the following diagram:
http://rollmeover.com/bronco_fab/amps/autotek/mx1500/Dlogixs/dlogix_4500_sch.pdf

 

[chrisg4]

I have the square waves on the emitters of Q902,903.

But still see them at gate pads on the outputs

 

[Perry Babin]

Do you have a square wave on the collectors of those transistors?

On the gates of the IRF7319?

 

[chrisg4]

I removed the IRF7319

get the below on G1 and G2

is it possible the irf7319 has failed?

G1

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scope setting

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G1

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G2

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[Perry Babin]

You can check it like any other FET.

What is the DC voltage on the two source legs?

 

[chrisg4]

S1: -5v
S2: 5v

 

[Perry Babin]

I think those are generally ±9v but since they're of equal value, they're likely OK.

Did you check the FET?

 

[chrisg4]

I did check it no shorts but i replaced it and I'm getting the square waves on the gates

 

[Perry Babin]

Are you also getting a square wave on the drains?

 

[chrisg4]

Yes the drains have good square waves but the gates are not so perfect... will uploads pics

 

[chrisg4]

Low side gate

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high side gate

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drains of the irf7319 (not seen on the drains of the fet pads - outputs are not installed)

An externally hosted image should be here but it was not working when we last tested it.