Hi!
Got this one from a friend of mine, with blown output transistors. I removed the output devices, replaced the blown fuses and proceeded with testing each transistor in the output section, out of circuit with a DMM in diode test mode - all of them seemed fine, so I put them back in. I checked most of the resistors in circuit, and the values read was realistic.
I powered the amplifier up with output devices desoldered, and measured with a DMM on emitter, collector and base's shoud be - but they seem odd to me, and I cant find anything about what to expect in the schematics. Can anyone tell med what to expect at ECB ?
Here is my test results, and link to schematics: Luxman-L230 amp .pdf - PDF Archive
The voltage at the collectors is obviously correct as they are connected directly to rail, but what about the others? Especially the high Base voltage.
Q112a E +433 mV
Q112a C +49,4 V
Q112a B -47,9 V
Q113a E +428 mV
Q113a C -49,2 V
Q113a B -47,7 V
Q112b E +358 mV
Q112b C +49,2 V
Q112b B -46,2 V
Q113b E +358 mV
Q113b C -49 V
Q113b B -47,5 V
Got this one from a friend of mine, with blown output transistors. I removed the output devices, replaced the blown fuses and proceeded with testing each transistor in the output section, out of circuit with a DMM in diode test mode - all of them seemed fine, so I put them back in. I checked most of the resistors in circuit, and the values read was realistic.
I powered the amplifier up with output devices desoldered, and measured with a DMM on emitter, collector and base's shoud be - but they seem odd to me, and I cant find anything about what to expect in the schematics. Can anyone tell med what to expect at ECB ?
Here is my test results, and link to schematics: Luxman-L230 amp .pdf - PDF Archive
The voltage at the collectors is obviously correct as they are connected directly to rail, but what about the others? Especially the high Base voltage.
Q112a E +433 mV
Q112a C +49,4 V
Q112a B -47,9 V
Q113a E +428 mV
Q113a C -49,2 V
Q113a B -47,7 V
Q112b E +358 mV
Q112b C +49,2 V
Q112b B -46,2 V
Q113b E +358 mV
Q113b C -49 V
Q113b B -47,5 V
Which transistor was faulty? The E B voltages can be no more than 0.7V! C E can be 50 or so. Please check your pinouts.
I've measure between ground and E, C, and B (or the place they should be)
Should I measure between E/B & C/E instead?
Should I measure between E/B & C/E instead?
As Jon says, you should never see more than around 650 to 800mv across any B-E junction.
Those readings don't compute in any sense.
Those readings don't compute in any sense.
If I understand your opening post correctly, you have no output devices installed. Your base voltage is high because there are no output devices installed.
You can temporarily install a couple 100R 1W resistors from B to E pads to check driver operation (no load). You should see close to zero offset on the output and the amp should pass signal like this, again, no load. Like this the drivers will be acting as outputs.
You can temporarily install a couple 100R 1W resistors from B to E pads to check driver operation (no load). You should see close to zero offset on the output and the amp should pass signal like this, again, no load. Like this the drivers will be acting as outputs.
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jwilhelm: Yes, you are correct, no output devices installed.
I did as you suggested - read close to zero at output, and between 500mV - 700mV at base as Jon and Mooly wrote.
Thank you guys, I will proceed with installing new output devices for one channel when they arrive in the mail in the next couple of days, and get back to you with the results! 🙂
I did as you suggested - read close to zero at output, and between 500mV - 700mV at base as Jon and Mooly wrote.
Thank you guys, I will proceed with installing new output devices for one channel when they arrive in the mail in the next couple of days, and get back to you with the results! 🙂
The base to emitter voltage(VEBO) of the output devices is what should set the voltage reading between base and emitter pads. When you install the output devices, you will see this measurement become more uniform.
Seeing zero on the output with the resistors installed tells you the drivers are both operating. If one was open or shorted, voltage would drift towards one of the rails.
Seeing zero on the output with the resistors installed tells you the drivers are both operating. If one was open or shorted, voltage would drift towards one of the rails.
Remember to use a bulb tester when initially powering up with your new outputs fitted. It can save them failing if there is a problem.
I will definately do that. Thanks for the reminder. What wattage would you prefer for this particular amplifier? Is 100W a good all-round or should I use a lower wattage bulb?
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