Directed 1500D

[mike49504]

They are both LM393's

Pin 1:.06
Pin 2:4.99
Pin 3:8.12
Pin 4:0
Pin 5:4.97
Pin 6:4.20
Pin 7:0.6
Pin 8:13.96


Pin 1:.06
Pin 2:13.13
Pin 3:2.90
Pin 4:0
Pin 5:3.70
Pin 6:3.23
Pin 7:0.06
Pin 8:13.96

 

[Perry Babin]

Is there a PNP transistor with it's collector connected to pin 2 of the second comparator (via a resistor)?

If so, remove that transistor and post the voltage on the second comparator again.

 

[mike49504]

Pin 1:4.96
Pin 2:0
Pin 3:2.99
Pin 4:0
Pin 5:4.38
Pin 6:3.24
Pin 7:4.96
Pin 8:13.75

 

[Perry Babin]

Reinstall the first transistor you removed (driving pin 4). The amp should come on as it's doing now.

Is the last PNP transistor that you pulled defective (check it carefully)?

Is there any DC offset across the speaker terminals?

Is there any DC offset between the secondary center tap and the main ground?

 

[mike49504]

No DC on the speaker terminals..

From secondary center tap to main ground I get 2.75 volts

 

[Perry Babin]

Is the last PNP transistor that you pulled defective (check it carefully)?

 

[mike49504]

In diode check heres what i get..

1-2:OL
1-3:OL
2-3:OL

Probes reversed

1-2:OL
1-3:0.670
2-3:0.664

 

[Perry Babin]

It's probably OK.

Reinstall it and connect a jumper between the secondary CT and the main ground. Does that make the amp power up normally?

What's the resistance between the RCA shields and the secondary CT (no jumper)?

 

[mike49504]

On the left RCA shield to secondary center tap: 0.3 ohms

Right rca shield to center tap:0.466 K ohms


With a jumper between Secondary center tap and main ground And the transistor back in amp doesnt power up it is in protection

 

[Perry Babin]

You need to find the equivalent of Q270 and Q271. Finding the ones with their collectors connected together and their base and emitters connected together should make it easier. When you find them, remove them to see if they amp will power up. If it does, check each one carefully.