If you have +20v on the speaker terminal (black meter probe on the secondary center tap of the power transformer and red probe on the 3rd leg of the output transistors of the defective channel), either the NPN transistor is leaking (electrically - not likely since it's new) or it's being driven on by another component. Measure the DC voltage from leg 1 to leg 3 of the NPN output transistor. What is the voltage from 1-3 (black probe on 3)?
What is the voltage from 1-3 on the PNP output (red probe on leg 3)?
What is the voltage from 1-3 on the PNP output (red probe on leg 3)?
If that's the case, it appears that you have no negative rail voltage. Look for broken connections on the wire jumpers leading from the rectifiers to the center leg of the PNP output transistor.
Also confirm that you have less than 1 ohm between leg 3 of the NPN output transistor and leg 3 of the PNP output transistor.
If there is a defective driver or other component, the amp may draw significant current when the connection to the rails is restored. Have the transistors tightly clamped to the sink when you power it up.
Also confirm that you have less than 1 ohm between leg 3 of the NPN output transistor and leg 3 of the PNP output transistor.
If there is a defective driver or other component, the amp may draw significant current when the connection to the rails is restored. Have the transistors tightly clamped to the sink when you power it up.
With the amp off, measure the resistance between the center legs of the NPN output transistors on opposite sides of the amp. You should read ~0 ohms.
Do the same for the PNP outputs. You should read 0 ohms between the center legs but it's likely that you won't. If you don't read ~0 ohms, there is an open connection.
Do the same for the PNP outputs. You should read 0 ohms between the center legs but it's likely that you won't. If you don't read ~0 ohms, there is an open connection.
I read the voltage wrong. You had a leading 0 on the number and I took it as 0.39.
The following schematic should be similar to yours. You'll have to work out which component is which but it should be simple enough on this amp using an ohm meter.
You can right-click to zoom in on the file.
http://www.bcae1.com/temp/unknownaudiobahn01.swf
Print this out and label the transistors with the designations on your board so it will be less confusing. If you don't know how to read a schematic, compare the voltages on the transistors that are connected together to see where the voltages vary significantly and post your findings.
The following schematic should be similar to yours. You'll have to work out which component is which but it should be simple enough on this amp using an ohm meter.
You can right-click to zoom in on the file.
http://www.bcae1.com/temp/unknownaudiobahn01.swf
Print this out and label the transistors with the designations on your board so it will be less confusing. If you don't know how to read a schematic, compare the voltages on the transistors that are connected together to see where the voltages vary significantly and post your findings.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.