power amplifier

[rickg289]

Hello all and a Merry Christmas and a Happy New Year!
I own a Luxman L580 amplifier that will not power up. I have checked all fuses. Caps look good. I measured the 2 large rail ones and they were fine(I have a capacitance meter) I don't hear the power on relays familiar 5-7 second click? Can any one assist me further? I apologize for the length of this post as it is my first. Thanks again

[mnemneth]

Welcome to the forum.

If your power on circuit isn't working then logically, either that circuit is faulty (unlikely) or more likely, you have a transformer/bridge fault that is stopping it operating..

Just testing electrolytics is a bit of a lottery unless they are really good quality, so I'd take your cap reading with a pinch of salt.

You need to measure the actual rail voltages across the caps when the amp is powered up.

NOTE. Take care as amplifier voltages can be LETHAL.

Only if you verify the rails are OK should you start looking at other faults.

Sandy

[rickg289]

Hi Sandy - I measured the rail voltage on the large filter caps + - 65.8 Volt DC.
This is not the easiest without a schematic! lol

[AndrewT]

switch off and allow the capacitor charge to fully dissipate.
Attach a DMM to the output and set to 20Vdc.

Switch on and see if there is any response at the DVM.

Look for an output relay.

Find the coil pins.
Find the NO pins and the NC pins.
Attach DVM to the coil pins, set to 20Vdc.
Switch on. Any response at the DVM

[rickg289]

I couldn't really find the output relay connections without taking things apart. However while I was checking voltages (B1,B2,B3) are present, I checked directly on the output transistors. The one side was 65 vdc on the collector and measured 10.5 vdc and 11.4 vdc on base and emitter respectively. The other side has 65vdc on the collector and 0vdc on both base and emitter. Can this be causing the amp to not start up? Once again thans...Rick

[mnemneth]

Originally Posted by rickg289

I couldn't really find the output relay connections without taking things apart. However while I was checking voltages (B1,B2,B3) are present, I checked directly on the output transistors. The one side was 65 vdc on the collector and measured 10.5 vdc and 11.4 vdc on base and emitter respectively. The other side has 65vdc on the collector and 0vdc on both base and emitter. Can this be causing the amp to not start up? Once again thans...Rick

Hi Rick.
If you can, try what Andrew said.

However, the info above would certainly point to an issue in the Amp circuitry.

Please clarify what you mean by "65v"!

Do you mean +65v on one side and -65v on the other?

As you have different base/emitter voltages, Andrew's suggestion of output DC offset becomes the likely problem.

Make sure your PSU has discharged then try the usual transistor tests on base/collector/emitter, testing the "probably" goos side first as an indicator and compare values.

If the values you get are wildly different one side to the other, then remove each transistor in turn from the board and test it out of circuit.

DO MAKE SURE YOUR PSU IS DISCHARGED AND THE PLUG OUT OF THE WALL!!!

Sandy

[djk]

Check for DC voltage on the output of the amplifier ahead of the relay (on the emitter resistors is a good test point).

If there is none, the small electrolytics in the protection circuit are dried out and need to be replaced. This is common. I would replace all the small electrolytics in the entire amplifier.